P4
Describe internal and total internal reflection using ray diagrams.
- Internal: Some light rays leave the glass box, but the weaker light rays reflect back. - Total internal: The strong light rays are all reflected back Internal reflection: when a beam of light leaves a glass block and enters the air, it refracts away from the normal due to an increase in its speed. During this refraction, a small amount of the light reflects off the back surface. This is called internal reflection When the angle of incidence is large enough, something unexpected happens. The beam of light does not leave the glass block. Instead, all of the light reflects back into the block as if the surface was a perfect mirror. This reflection effect is called total internal reflection . Total internal reflection can only happen at a boundary where: the wave speeds up after it passes across the boundary (e.g. a wave passing from glass to air) the angle of incidence of the wave on the boundary is larger than the critical angle (c). Internal reflection: When light travels from a denser medium to a rarer medium and is incident at an angle more than the critical angle for that medium, it is completely returned inwardly in the denser medium. This complete inward return of light is called total (complete) internal (inward) reflection (return). Sometimes, when light is moving from a denser medium towards a less dense one, instead of being refracted, all of the light is reflected. This phenomenon is called total internal reflection. Total internal reflection: Total internal reflection is the phenomenon of bouncing back of light in the same medium after striking the boundary of a rarer medium. This happens when the angle of refraction exceeds 90∘ In such a case Snell's law becomes invalid and reflection takes place instead of refraction. Total internal reflection, or TIR as it is intimately called, is the reflection of the total amount of incident light at the boundary between two media. otal internal reflection is a phenomenon of reflection of ray back to the same medium when passing from denser medium to rarer medium in a such away that angle of incidence greater than its critical angle. When a light ray reaches the boundary between two transparent materials it may be refracted . In this situation, the ray is reflected inside the more dense medium, following the law of reflection. ... This is called total internal reflection (TIR) .
State the approximate range of audible frequencies for a healthy human ear is
20 Hz to 20000 Hz.
Demonstrate understanding that waves transfer energy without transferring matter.
All waves transfer energy but they do not transfer matter. A wave transfers energy from one place to another without transferring matter in the process. Energy is transferred in waves through the vibration of particles, but the particles themselves move in a perpendicular fashion to the horizontal movement of the wave. Energy is transformed between potential (stored) and kinetic (movement) energy as the particles go from rest to movement and back to rest. A wave transports its energy without transporting matter. Energy is transported through the medium, yet the particles are not transported. The particles 'take part' in the wave by bumping into one another and transferring energy. This is why energy can be transferred, even though the average position of the particles doesn't change.
Describe the use of water waves to demonstrate diffraction.
Diffraction can be demonstrated by placing small barriers and obstacles in a ripple tank and observing the path of the water waves as they encounter the obstacles. The waves are seen to pass around the barrier into the regions behind it; subsequently the water behind the barrier is disturbed. The effect is greatest when the wavelength of the waves is similar in size to the gap or object size. Notice that the wavelength is the same on both sides - spreading out does not alter the speed of the wave, so the wavelength is unchanged. "Wave diffraction is considered here to be the phenomenon in which water waves are propa gated into a sheltered region formed by a breakwater or similar barrier which interrupts a portion of an otherwise regular wave train. Start with straight ripples striking a straight barrier, at an angle. Continue with a single straight ripple, then a curved ripple. To show refraction with a ripple tank, you need to show how ripples change speed when travelling from deeper into shallower water (or vice versa).
Describe how the reflection of sound may produce an echo.
Echoes. An echo is a sound that is repeated because the sound waves are reflected back. Sound waves can bounce off smooth, hard objects in the same way as a rubber ball bounces off the ground. Although the direction of the sound changes, the echo sounds the same as the original sound. Reflection of sound waves also leads to echoes. Echoes are different than reverberations. Echoes occur when a reflected sound wave reaches the ear more than 0.1 seconds after the original sound wave was heard.
State that all electromagnetic waves travel with the same high speed in a vacuum and approximately the same in air.
Electromagnetic waves are transverse waves but they have some unusual properties which other transverse waves do not. Electromagnetic waves can travel through a vacuum (empty space) which means they do not rely on the vibration of any kind of particle to travel. In fact, electromagnetic waves are vibrations in linked electric and magnetic fields moving through space. Electromagnetic waves travel at very, very high speeds - much faster than any other type of wave. Electromagnetic waves are waves that can travel through a vacuum (empty space). They don't need a medium or matter. They travel through electrical and magnetic fields that are generated by charged particles. All electromagnetic waves travel at the same speed in a vacuum - at 3.0 × 10 8 m/s (300 000 000 m/s). This is the fastest speed possible for anything to travel - fast enough for an electromagnetic wave to travel around the circumference of the Earth seven and a half times in one second. Electromagnetic waves travel at almost the same speed in air but move more slowly in other materials. In glass, for example, visible light travels at approximately 2.5 × 10 8 m/s. The electromagnetic waves are not mechanical waves. There are vibrations of electric vector and magnetic vector in them. These vibrations do not need any particles present in the medium for their propagation. That's why electromagnetic waves do not require any medium for propagation. The speed of these EM waves only changes when the medium changes. In vacuum, EM waves travel at their maximum speed of approximately 3.00⋅108ms . In air, this speed is slightly lower but very close to the above value. Electromagnetic radiation is a type of energy that is commonly known as light. Generally speaking, we say that light travels in waves, and all electromagnetic radiation travels at the same speed which is about 3.0 * 108 meters per second through a vacuum. All electromagnetic waves travel at the same speed through empty space. That speed, called the speed of light, is about 300 million meters per second (3.0 x 108 m/s). Nothing else in the universe is known to travel this fast. The speed of a wave is a product of its wavelength and frequency. Because all electromagnetic waves travel at the same speed through space, a wave with a shorter wavelength must have a higher frequency, and vice versa. This relationship is represented by the equation: Speed = Wavelength × Frequency. State that the speed of electromagnetic waves in a vacuum is 3.0 x 108 m/s.
Describe the formation of an optical image by a plane mirror and give its characteristics.
How do we see objects in the mirror? It is due to reflection (of light). Light rays will strike the mirror and reflect off it into our eyes. The optical image formed will be: the same size as the object. upright virtual - a real image is formed on a screen (or some other detector, like your eyes) when all of the rays from a single point on an object strike a single point on a screen. A virtual image is produced when rays of light come into our eyes and appear to come from an object, when in reality, that object is not present at the apparent position of the source. So, due to the direction the light rays come from, our brain makes us think that the object is in one place when in reality, it is in another. The most common example of virtual images are reflections in plane mirrors - look at the diagram below. It looks like the object is at Q'Q, when it's actually at P'P. The image will be behind the plane of the mirror and the object will be in front; the distance between the image and mirror will be equal to the distance between the object and mirror. This is shown in the diagram. do is equal to di. optical image, the apparent reproduction of an object, formed by a lens or mirror system from reflected, refracted, or diffracted light waves. There are two kinds of images, real and virtual. In conclusion, plane mirrors produce images with a number of distinguishable characteristics. Images formed by plane mirrors are virtual, upright, left-right reversed, the same distance from the mirror as the object's distance, and the same size as the object. Virtual images form when light rays from the same location on an object reflect off a mirror and diverge or spread apart. Real images form when light rays from the same location on an object reflect off a mirror and converge or come together.
Describe transmission of sound in air in terms of compressions and rarefactions.
In this way, the vibrating surface emits alternating waves of compression and rarefaction, which together make up a sound wave. Overal, during the emission of a sound wave, air particles tend to vibrate back and forth around a fixed point, parallel to the direction that the wave travels in. When sound wave travels through a medium, say air, the particles of medium disturb in the same fashion, i.e. compression and rarefaction (depression). When air particles come closer it is called compression. On the other hand, when particles go farther than their normal position it is called rarefaction. The compressions are closer together when its loud. The rarefaction particles are further apart when the sound is soft. Sound waves traveling through air are indeed longitudinal waves with compressions and rarefactions. Since air molecules (the particles of the medium) are moving in a direction that is parallel to the direction that the wave moves, the sound wave is referred to as a longitudinal wave. The result of such longitudinal vibrations is the creation of compressions and rarefactions within the air.In compressionons, the medium particles are close together while in rarefactions, the meduim particles are far apart. The source of the wave imparts energy to the particles(molecules) of the medium in contace with the source. When this energy is imparted to the nearest particles, these particles begin to move.
Converging and diverging lenses Describe the action of a thin converging lens on a beam of light.
Lens: A lens is a shaped piece of transparent material designed to refract beams of light in a particular way. Most lenses are smoothly curved surfaces made from glass, but lenses can be made from any transparent material such as plastics or even cells and proteins which make up the lenses in your eyes. There are two types of lenses, concave and convex. The characteristics of the images formed by a converging lens depend on the position of the object, especially whether the object is inside or outside the focal length of the lens. This experiment will allow you to find these characteristics. Convex lenses are also known as converging lenses since the rays converge after falling on the convex lens while the concave lenses are known as diverging lenses as the rays diverge after falling on the concave lens. Convex lenses refract light inward toward a focal point. Light rays passing through the edges of a convex lens are bent most, whereas light passing through the lens's center remain straight. Convex lenses are used to correct farsighted vision. Convex lenses are the only lenses that can form real images. A lens is a transparent object that causes the light that passes through it to refract. A converging lens that is curved on both sides (there are two types of converging lens- concave and convex.) A converging lens causes the light rays that are travelling parallel to its principal axis to refract and cross the principal axis at a fixed point called the focal point. (This is explained in more detail below). (A ray diagram is given below) It should also be noted that converge is a word that describes the tendency of two lines to meet. A converging lens causes the light rays that are travelling parallel to its principal axis to refract and cross the principal axis at a fixed point called the focal point. These rays of light will refract when they enter the lens and refract when they leave the lens. As the light rays enter into the more dense lens material, they refract towards the normal; and as they exit into the less dense air, they refract away from the normal. Thin lenses can be converging or diverging. Converging lenses are thicker in the middle than near the edges, and diverging lenses are thicker near the edges than in the middle. A thin lens has two focal points, located on the optical axis, a distance f from the center of the lens on either side of the lens. If refracted rays converge to a single point after refraction, then this is called as converging behaviour of the lens. This is observed when a real image is formed. These can be used in applications when all intensity of light is to be focussed at a point. A converging lens produced a virtual image when the object is placed in front of the focal point. For such a position, the image is magnified and upright, thus allowing for easier viewing. Converging lenses are lenses which converge the light rays coming towards them, whereas diverging lenses are lenses which diverge the rays coming towards them. A converging lens have positive focal length. A converging lens causes exiting rays to be more convergent coming out than they were entering the lens. A converging lens can form a real image or a virtual image of a real object. Only when the object is a distance from the lens greater than the focal length will a real image be formed. A diverging lens always forms virtual images of real objects. Diverging lenses: a lens that causes a beam of parallel rays to diverge after refraction, as from a virtual image; a lens that has a negative focal length. The concave lens is a diverging lens, because it causes the light rays to bend away (diverge) from its axis. In this case, the lens has been shaped so that all light rays entering it parallel to its axis appear to originate from the same point, F, defined to be the focal point of a diverging lens. A diverging lens always forms virtual images of real objects. Only when incident rays are very convergent entering a negative lens (convergent toward a point somewhere between the lens and the focal point on the far side of the lens), can the emergent rays still be convergent, forming a real image. When parallel rays of light enter a concave lens, the light waves refract outward, or spread out. The light rays refract twice: first when entering the lens and second when leaving the lens. Only the light rays passing through the center of the lens remain straight. A diverging lens is a lens that diverges rays of light that are traveling parallel to its principal axis. Diverging lenses can also be identified by their shape; they are relatively thin across their middle and thick at their upper and lower edges. A lens refracts light and forms an image. A concave lens is thicker at the edges than it is in the middle. This causes rays of light to diverge. The light forms a virtual image that is right-side up and smaller than the object. Focal point/principal of focus: Principal focus or the focal point is the point where rays of light travelling parallel to the principal axis intersect the principal axis and converge. the point at which rays or waves meet after reflection or refraction, or the point from which diverging rays or waves appear to proceed. A converging lens that is curved on both sides (there are two types of converging lens- concave and convex.) A converging lens causes the light rays that are travelling parallel to its principal axis to refract and cross the principal axis at a fixed point called the focal point. A focal point is a common point on the principal axis where all the light rays starting from the object converge. The focal point has a spatial extent known as the blur circle. This non-ideal focusing may occur due to aberrations of the imaging optics Focal length: Focal length is the distance between the vertical axis of the lens and the focal point. The distance from the lens to the principal focus is called the focal length . Optical axis: optical axis, the straight line passing through the centre of a lens and joining the two centres of curvature of its surfaces. Sometimes the optical axis of a lens is called its principal axis. The path of a light ray along this axis is perpendicular to the surfaces and, as such, will be unchanged. Optical axis of a lens is an imaginary straight line which passes through the geometrical centre of a lens joining the two centres of curvature of surfaces of lens. The optical axis of our eye is the line passing through the cornea as well as the centre of all the elements of the eyeball.
Describe the main features of the electromagnetic spectrum in order of frequency, from radio waves to gamma radiation (ɣ).
Radiowaves, Microwaves, Infra-red, Visible light, Ultra-violet, X-rays, Gamma rays. Wavelength, Frequency and energy: The electromagnetic spectrum is generally divided into seven regions, in order of decreasing wavelength and increasing energy and frequency. From this equation, it is clear that the energy of a photon is directly proportional to its frequency and inversely proportional to its wavelength. Thus as frequency increases (with a corresponding decrease in wavelength), the photon energy increases and visa versa. The electromagnetic spectrum is generally divided into seven regions, in order of decreasing wavelength and increasing energy and frequency. The sequence from longest wavelength (radio waves) to shortest wavelength (gamma rays) is also a sequence in energy from lowest energy to highest energy. Remember that waves transport energy from place to place. The energy carried by a radio wave is low, while the energy carried by a gamma ray is high. Gamma, X-Rays, UV, Visible, Infrared, Microwaves, Radio Waves. in order from highest to lowest energy, the sections of the EM spectrum are named: gamma rays, X-rays, ultraviolet radiation, visible light, infrared radiation, and radio waves.
Understand that refraction is caused by a change of speed as a wave moves from one medium to another.
Rarefaction is the reduction of an item's density, the opposite of compression. Like compression, which can travel in waves (sound waves, for instance), rarefaction waves also exist in nature. A common rarefaction wave is the area of low relative pressure following a shock wave (see picture). Longitudinal waves show areas of compression and rarefaction : compressions are regions of high pressure due to particles being close together. rarefactions are regions of low pressure due to particles being spread further apart. It is the action or process of rarefying. 2 : the quality or state of being rarefied. 3 : a state or region of minimum pressure in a medium traversed by compressional waves (such as sound waves). When a vibrating object moves backward in air as medium, it creates a region of low pressure. This region is called a rarefaction. Compression is that part of longitudinal wave in which the medium of particles are closer and there is momentary decrease in volume of medium. Rarefaction is that part of longitudinal wave in which the medium of particles apart and there is momentary increase in volume of medium. Physics. When a vibrating object goes forward in air as medium it pushes and compresses the air. This is the compression. When a vibrating object goes back in air as medium it creates a region of low pressure. This is the rarefaction. Rarefaction (definition) places where molecules of air are not squeezed and are spread out (opposite of compression). efraction is caused due to the change in speed of light when it enters from one medium to another. When the light goes from air into water, it bends towards the normal because there is a reduction in its speed. Refraction is caused due to the change in speed of light when it enters from one medium to another. When the light goes from air into water, it bends towards the normal because there is a reduction in its speed. refraction, in physics, the change in direction of a wave passing from one medium to another caused by its change in speed. For example, waves travel faster in deep water than in shallow.
Recall and use the definition of refractive index n in terms of speed.
Ratio of the speed of wave in a vacuum to the speed of wave in a given medium. The refractive index of a medium (n) is equal to the speed of light (c) divided by the velocity of light through the medium (v). Rearranging the equation allows us to see the relationship regarding v. The lower the refractive index, the faster the velocity of light. Medium A has the smaller refractive index. Refractive index is also equal to the velocity of light c of a given wavelength in empty space divided by its velocity v in a substance, or n = c/v. The refractive index of a medium is inversely proportional to the velocity of light. It means as the refractive index of a medium increases, the speed of light going through that medium decreases. the ratio of the velocity of light in a vacuum to its velocity in a specified medium. What is the 'refractive index'? The refractive index of a medium (glass, water) is defined as the speed of light in a vacuum divided by the speed of light in the medium. Refractive index is defined as the ratio of the speed of light in a vacuum to its speed in a specific medium. n = Refractive index. c = Velocity of light in a vacuum ( 3 × 108 m/s). v = Velocity of light in a substance. Refractive index is usually represented by the symbol n, or sometimes μ . where c is the speed of light in a vacuum and v the speed of light in the material. Refractive index of a medium is the ratio of the speed of light in vacuum to the speed of light in the medium. Therefore, it has no units. The ratio of the velocities or speed of light in different media gives the refractive index. The refractive index is of two types: Absolute Refractive Index. Relative Refractive Index. The refractive index is the extent to which light is refracted when it enters a medium. refractive index, also called index of refraction, measure of the bending of a ray of light when passing from one medium into another. Refraction occurs when light passes a boundary between two different transparent media. At the boundary, the rays of light undergo a change in direction. The direction is taken as the angle from a hypothetical line called the normal.
Describe the difference between a real image and a virtual image.
Real image: real image is defined as one that is formed when rays of light are directed in a fixed point. A real image can be projected or seen on a screen. Real images are obtained using a converging lens or a concave mirror. The size of the real image depends upon the placement of the object. Real images are those where light actually converges, whereas virtual images are locations from where light appears to have converged. Real images occur when objects are placed outside the focal length of a converging lens or outside the focal length of a converging mirror. When an image is formed on a screen with the help of a mirror, it is called a Real Image. Similarly, an image which can't be obtained on a screen with the help of a mirror, it is called Virtual Image. A real image is produced by an optical system (a combination of lenses and/or mirrors) when light rays from a source cross to form an image. Light rays diverge from the real image in the same way that they diverge from the source. An image that is formed when the light rays from an object do not meet but appear to meet behind the lens and cannot be projected onto a screen. A virtual image is formed by the divergence of light away from a point. A real image is an image that can be projected onto a screen. A virtual image appears to come from behind the lens. To draw a ray diagram : Draw a ray from the object to the lens that is parallel to the principal axis. Once through the lens, the ray should pass through the principal focus. A real image is the collection of focus points actually made by converging rays, while a virtual image is the collection of focus points made by extensions of diverging rays. In other words, it is an image which is located in the plane of convergence for the light rays that originate from a given object. Virtual image: A virtual image is an upright image that is achieved where the rays seem to diverge. A virtual image is produced with the help of a diverging lens or a convex mirror. an image (such as one seen in a plane mirror) formed of points from which divergent rays (as of light) seem to emanate without actually doing so. Virtual image refers to the image which forms when the light rays appear to meet at definite point, after reflection from the mirror. An erect image is one that appears right-side up. An erect image is formed by the actual intersection of rays. Since the virtual images are due to imaginary rays, they are drawn using broken lines. No light ever reaches a virtual image. Examples of virtual image: Image formed in a plane mirror, image formed on the front and back surfaces of a spoon, etc. The image behind the mirror is called a virtual image because it cannot be projected onto a screen—the rays only appear to originate from a common point behind the mirror. If you walk behind the mirror, you cannot see the image, because the rays do not go there. Virtual means it appears to be real although it may not have a physical presence. A virtual object is usually associated with optical systems like we get virtual images. Virtual Image: Images that cannot be formed on a screen is called virtual image. Eg:images formed in a plane mirror. What is the difference between Real and Virtual Image? The image formed when rays of light meet at a point after reflection/refraction is called real image. The image formed when rays of light appear to meet (when diverging rays are extended) at a point is called a virtual image. Real images are obtained using a converging lens or a concave mirror. The size of the real image depends upon the placement of the object. A virtual image is an upright image that is achieved where the rays seem to diverge. A virtual image is produced with the help of a diverging lens or a convex mirror.
Describe the nature of an image using the terms enlarged/same size/diminished and upright/inverted.
Real images are formed on a screen (or another detector, like your eyes) when all of the light rays from a single point on an object hits a single point on the screen. In virtual images, on the other hand, are produced when light enters our eyes that appear to come from a real object when in reality, there is no object at the apparent source. Reduced means that the image is smaller than the object and enlarged means that the image is larger than the object. The position of the object is described in terms of the number of focal lengths between the optic centre and the object. Inverted: Inverted means that the image is upside down and upright obviously means that the image is the right way up. Diminish means to make smaller or lesser. If you cover a lightbulb with a dark lamp shade, the light from the lamp will diminish. It can also mean become less important. Once the light has been dimmed, its role in lighting the room is diminished. What causes lenses to make inverted images? The image appears inverted and smaller when the light is focused at a point beyond the lens's focal length. Microscopes and telescopes have compound lenses (multiple lenses with the same focal point), which allow us to see small things much larger and in the right orientation. Convex: As you decrease the distance between the object and the lens below the focal length of the lens the image will flip back. Concave: For an object viewed through a concave lens, light rays from the top of the object will be refracted and will diverge on the other side of the lens. These rays will appear: from the same side of the principal axis, meaning the image will be upright. what makes the size increase? It was observed that when the distance between an object and a lens decreases, the size of the image increases. A convex lens is one that increases the size of the image as the distance between the object and the lens decreases which is a converging lens. The lens having more thickness alters the path of light more effectively and due to bending of light, the focal length decreases. So, the more thicker is the lens, the more light will bend and will thus decrease the focal length. You can simply write: The more thick is the lens, the less focal length, it will have. Assuming lens are made of the same material, the thicker one will be able to bend the light more as the light travels through it for a longer period of time. As we know, greater the bending lesser the focal length, so thin one will have more focal length. objects will appear smaller in images taken with short focal length lenses, and larger in those with longer focal lengths The diagram shows that as the object distance is decreased, the image distance is decreased and the image size is increased. So as an object approaches the lens, its virtual image on the same side of the lens approaches the lens as well; and at the same time, the image becomes larger.
Show an understanding that a medium is needed to transmit sound waves.
Sound is a form of energy produced and transmitted by vibrating matter. Sound waves caused by such vibrations move through a medium (a solid, liquid, or gas) in all directions from their source. Sound needs a material medium for their propagation like solid, liquid or gas to travel because the molecules of solid, liquid and gases carry sound waves from one point to another. Sound cannot progress through the vacuum because the vacuum has no molecules which can vibrate and carry the sound waves. Of the three mediums (gas, liquid, and solid) sound waves travel the slowest through gases, faster through liquids, and fastest through solids. Temperature also affects the speed of sound. Gases: The speed of sound depends upon the properties of the medium it is passing through. Water and sound waves are mechanical and require a medium in order to travel. Light and radio waves are not mechanical but rather electromagnetic and do not need a medium. Sound travels fastest through solids. This is because molecules in a solid medium are much closer together than those in a liquid or gas, allowing sound waves to travel more quickly through it. In fact, sound waves travel over 17 times faster through steel than through air. Sound needs a material medium for their propagation like solid, liquid or gas to travel because the molecules of solid, liquid and gases carry sound waves from one point to another. Sound cannot progress through the vacuum because the vacuum has no molecules which can vibrate and carry the sound waves. a medium is required in order for sound waves to transport energy. Mechanical waves require a medium in order to transport energy. Sound, like any mechanical wave, cannot travel through a vacuum.
Describe the production of sound by vibrating sources.
Sound is produced when an object vibrates, creating a pressure wave. This pressure wave causes particles in the surrounding medium (air, water, or solid) to have vibrational motion. As the particles vibrate, they move nearby particles, transmitting the sound further through the medium. Sound is a form of energy which produces hearing sensation in our ears. Sound is produced by vibration of an object. They cause the neighboring particles to vibrate and so on. This process continues until the vibrations reach the person's ear and we are able to hear the sound. Sound is produced when an object vibrates, creating a pressure wave. This pressure wave causes particles in the surrounding medium (air, water, or solid) to have vibrational motion. As the particles vibrate, they move nearby particles, transmitting the sound further through the medium. A sound is a form of energy which produces a sensation of hearing in our ears. Propagation of Sound: Sound is produced by vibrating objects. Medium: The matter or substance through which sound is transmitted is called a medium. It can be solid, liquid or gas. sound, a mechanical disturbance from a state of equilibrium that propagates through an elastic material medium. When an object, like the string of a guitar, vibrates it produces a sound wave which travels through the air. The wave travels from the source (the guitar string) through a medium (the air) and reaches a detector (our ear). The wave then causes our ear drum to vibrate and this vibration passes through a series of tiny bones into our inner ear, stimulating nerve cells to send electrical signals to our brain. These signals cause the sensation of sound. The properties of the sound wave can vary depending on how the object producing the sound is vibrating. If the vibrations are made larger, by plucking the string harder, then the amplitude of the sound wave will become greater. Increasing the amplitude increases the energy transfer and so the sound will be louder. If the object is made to vibrate back and forth more times each second then it produces vibrations at a higher frequency. The pitch of the sound we hear will be higher. Change to the source of vibration: Faster vibrations What happens to the sound wave?: Increased frequency What happens to what we hear?: Increased pitch Change to the source of vibration: Larger vibrations What happens to the sound wave?: Increased amplitude What happens to what we hear?: Increased loudness Sounds are the result of air vibrating, and if they're reproduced at, say, twice the speed that they were originally recorded at, the vibrations hit our ear twice as many times per second - i.e. twice the original frequency, which makes them sound higher in pitch. Greater amplitude waves have more energy and greater intensity, so they sound louder. As sound waves travel farther from their source, the more spread out their energy becomes.
Describe the longitudinal nature of sound waves.
Sound waves are a type of longitudinal wave. The particles which form the wave move back and forth in the same direction as the wave travels. As the wave passes through the air, is produces regions where the air particles are compressed (pushed closer together); these are known as compressions. It also produces regions where the air particles are spread out slightly further than normal, known as rarefactions (Figure 2). The compressions and rarefactions move away from the source of the sound in all directions, spreading the sound wave outwards. Sound waves in air (and any fluid medium) are longitudinal waves because particles of the medium through which the sound is transported vibrate parallel to the direction that the sound wave moves. A vibrating string can create longitudinal waves as depicted in the animation below. Sound waves in air (and any fluid medium) are longitudinal waves because particles of the medium through which the sound is transported vibrate parallel to the direction that the sound wave moves. It can be difficult to imagine these compressions and rarefactions because air molecules are tiny, so you can't see them being squashed closer together. To help you picture the movement of a longitudinal wave similar to sound, you can produce rarefactions and compressions on a 'Slinky' spring. Stretch out the spring along a flat surface and then push and pull one end in and out. You will see a small compressed region move along the spring - a compression - and behind this you will see that the coils of the spring become slightly more spread out - a rarefaction. The compressions and rarefactions move along the length of the spring in a similar way to the compressions and rarefactions moving through the air.
State the meaning of speed, frequency, wavelength and amplitude.
Speed: Wave speed is the speed at which a wave travels. Wave speed is related to wavelength, frequency, and period by the equation wave speed = frequency x wavelength. The most commonly used wave speed is the speed of visible light, an electromagnetic wave. This equation shows how the three factors are related: Speed = Wavelength x Wave Frequency. In this equation, wavelength is measured in meters and frequency is measured in hertz (Hz), or number of waves per second. Therefore, wave speed is given in meters per second, which is the SI unit for speed. A wave is a disturbance in a medium that carries energy without a net movement of particles. It may take the form of elastic deformation, a variation of pressure, electric or magnetic intensity, electric potential, or temperature. The speed of a wave is related to its frequency and wavelength , according to this equation: v = f × λ where: v is the wave speed in metres per second, m/s. f is the frequency in hertz, Hz. The speed of the reflected pulse is the same as the speed of the incident pulse. The wavelength of the reflected pulse is the same as the wavelength of the incident pulse. The amplitude of the reflected pulse is less than the amplitude of the incident pulse. Frequency: In physics, the term frequency refers to the number of waves that pass a fixed point in unit time. It also describes the number of cycles or vibrations undergone during one unit of time by a body in periodic motion. Frequency describes the number of waves that pass a fixed place in a given amount of time. The frequency of a wave is the number of waves produced by a source each second. It is also the number of waves that pass a certain point each second. The unit of frequency is the hertz (Hz). Frequency is expressed in units of hertz (Hz) which is equivalent to one (event) per second. The frequency of a wave refers to how often the particles of the medium vibrate when a wave passes through the medium. Frequency is a part of our common, everyday language. frequency: Is the number of waves that pass a certain point in a specified amount of time. trough: The low point of the wave cycle. Wavelength: the distance between successive crests of a wave, especially points in a sound wave or electromagnetic wave. wavelength, distance between corresponding points of two consecutive waves. Wavelength is the distance between identical points (adjacent crests) in the adjacent cycles of a waveform signal propagated in space or along a wire. Wavelength: The distance between 2 consecutive crest or troughs is called Wavelength. It is represented by the symbol λ(lamda). Wavelength is defined as the minimum distance between two consecutive points in the same phase of wave motion. It is denoted by λ. In case of transverse wave we use the term crest for thepeak of the maximum displacement. The point of minimum displacement is known as trough. Amplitude: amplitude, in physics, the maximum displacement or distance moved by a point on a vibrating body or wave measured from its equilibrium position. The definition of amplitude refers to the length and width of waves, such as sound waves, as they move or vibrate. The amplitude of a wave refers to the maximum amount of displacement of a particle on the medium from its rest position. In a sense, the amplitude is the distance from rest to crest. Similarly, the amplitude can be measured from the rest position to the trough position. Amplitude is a measure of the wave's height. It also tells us how much energy a wave has. Waves with more energy have higher amplitudes. The amplitude of a sound wave determines the sound's loudness. The amplitude of a wave is defined as the maximum amount of displacement of a particle on the medium from its rest or equilibrium position. Amplitude is the maximum distance or displacement moved by a particle on a wave from its equilibrium position. Oscillation: Oscillation is defined as the process of repeating variations of any quantity or measure about its equilibrium value in time. Oscillation can also be defined as a periodic variation of a matter between two values or about its central value. Equilibrium: The equilibrium is represented by the horizontal line in the middle of the wave. One period is the time it takes to go for one cycle, which means to get from one crest to crest, trough to trough, or to and from corresponding equilibrium points (both equilibrium points same direction).
Use and describe the use of a single lens as a magnifying glass.
The image of an object is magnified through at least one lens in the microscope. This lens bends light toward the eye and makes an object appear larger than it actually is. A magnifying glass is a convex lens used to make an object appear much larger than it actually is. This works when the object is placed at a distance less than the focal length from the lens. A convex lens is used as a magnifying glass as it converges parallel beams of light into one concentrated beam of light. The distinguishing feature of the magnifying glass is its structure—a bi-convex lens (one that is convex on both sides) situated in a frame and attached to a handle. The lens may be constructed of glass or plastic, and the handle of materials such as wood, plastic, and metal. Magnifying lenses take parallel light rays in, then refracts it, so that they all converge as they exit. In layman's terms, light rays enter a lense next to each other and exit the lens intertwined — this creates the illusion that an image is larger than it really is. Magnifying lenses take parallel light rays in, then refracts it, so that they all converge as they exit. In layman's terms, light rays enter a lense next to each other and exit the lens intertwined — this creates the illusion that an image is larger than it really is. A simple light microscope manipulates how light enters the eye using a convex lens, where both sides of the lens are curved outwards. When light reflects off of an object being viewed under the microscope and passes through the lens, it bends towards the eye. This makes the object look bigger than it actually is. The first ray travels from the top of the object, parallel to the optical axis, until it reaches the lens. This ray then refracts so that it passes through the principal focus on the far side of the lens. The second ray is drawn from the top of the object and straight through the centre of the lens with no change in direction. The two rays do not actually meet so a real image is not formed. If we trace the rays back to where they seem to come from when viewed through the lens (shown by the dotted lines in Figure 4), we can see that the rays seem to meet on the same side of the lens as the object. As these rays did not actually travel along these dotted paths, we call them 'virtual rays'. Because the rays do not actually pass through the place where the image appears, we describe the image as a virtual image. We cannot put a screen at this point and see the image. It only appears if we look through the lens. The virtual image formed by the lens is upright (the same way up as the object) and has also been enlarged (or magnified). Because the image produced appears larger than the original object, the lens is acting as a magnifying glass. For a magnifying glass to operate correctly the object we are observing needs to be placed inside the focal length of the lens. This means that we need to place the magnifying glass close to the object for us to see the magnified image. This works when the object is placed at a distance less than the focal length from the lens. When they pass through a magnifying glass, the convex lens bends the parallel rays so that they converge and create a virtual image on your eyes' retinas. That virtual image on your retinas appears larger than the real object due to principles of geometry. A magnifying glass is usually a convex lens (a lens that bulges outwards), made of either glass or plastic. Light hits the glass at an angle, and it gets refracted towards the centre of the lens. Leaving the glass makes it refract even further, meaning, at some point, these rays of light converge together A magnifying glass is a convex lens used to make an object appear much larger than it actually is. This works when the object is placed at a distance less than the focal length from the lens. The image is: upright (the right way up) magnified (larger than the object) virtual (cannot be produced on a screen)
Give the meaning of critical angle.
The largest angle of incidence which allows light to escape the glass block is called the critical angle (c). If the light reaches the boundary at any angle greater than the critical angle, all the light will be reflected back into the glass block. Critical Angle: The angle of incidence which produces an angle of refraction of 900 (refracted ray is along the boundary of the surface). When the angle of incidence is greater than the critical angle, total internal reflection occurs (all light is reflected at the boundary). Light travels from glass to air. Angle of refraction is greater than angle of incidence. All light waves, which hit the surface beyond this critical angle, are effectively trapped. The critical angle for most glass is about 42°. critical angle, in optics, the greatest angle at which a ray of light, travelling in one transparent medium, can strike the boundary between that medium and a second of lower refractive index without being totally reflected within the first medium. For light travelling from glass into air the angle of refraction is greater than the angle of incidence. When the angle of refraction is exactly 90°, then the angle of incidence is called the critical angle C. The critical angle is the angle of incidence for which angle of refraction is 90°. Total internal reflection is the phenomenon that involves the reflection of all the incident light off the boundary. The critical angle of a medium can be defined as the angle of incidence of a light ray in the denser medium which is such that the angle of refraction obtained is equal to 90.
Recall and use the law of reflection: angle of incidence i = angle of reflection r Recognising these angles are measured to the normal.
The law of reflection states that the incident ray, the reflected ray, and the normal to the surface of the mirror all lie in the same plane, and that the angle the incident ray makes with the normal is equal to the angle that the reflected ray makes to the same normal. The light ray that hits the mirror from the object is called the incident ray (ray of incidence) and the ray that is reflected off the mirror into our eyes is called the reflected ray (ray of reflection). The normal is the line that runs perpendicular to the mirror between the two rays. The angle of incidence is the angle between the normal and incident ray, and the angle of reflection is the angle between the normal and the reflected ray. The law of reflection states that when a ray of light reflects off a surface, the angle of incidence is equal to the angle of reflection. The law of reflection states that the reflected ray, the incident ray and the normal all lie in the same plane. therefore, the angle of reflection is equal to the angle of incidence. An incident ray of light hits a plane mirror at an angle and is reflected back off it. The angle of reflection is equal to the angle of incidence. The angle of incidence is the angle between this normal and the incident ray; the angle of reflection is the angle between this normal and the reflected ray. According to the law of reflection, the angle of incidence equals the angle of reflection.
Relate the loudness and pitch of sound waves to amplitude and frequency.
The pitch of a sound depends on the frequency while loudness of a sound depends on the amplitude of sound waves. The pitch of a sound is related to frequency, which is related to the wavelength of a wave. The higher the frequency (shorter wavelength), the higher the pitch. The loudness of a sound wave is related to the amplitude. A bigger amplitude results in a louder sound. The sensation of a frequency is commonly referred to as the pitch of a sound. A high pitch sound corresponds to a high frequency sound wave and a low pitch sound corresponds to a low frequency sound wave. Sound amplitude causes a sound's loudness and intensity. The bigger the amplitude is, the louder and more intense the sound. Higher the amplitude of sound, the louder the sound is and higher the frequency of sound waves, higher the pitch of the sound will be. Pitch and loudness of sound. Sound B has a lower pitch (lower frequency) than Sound A and is softer (smaller amplitude) than Sound C. The frequency of a sound wave is what your ear understands as pitch. A higher frequency sound has a higher pitch, and a lower frequency sound has a lower pitch.
Describe and explain the action of optical fibres particularly in medicine and communications technology.
Total internal reflection is a very useful effect as it allows us to direct light to travel in any path we want. This effect is used in optical fibres. These are very thin glass or plastic tubes which can bend. In communications systems, a glass fibre is used to transmit optical pulses over very long distances. A very short pulse of light is produced at one end of the fibre. The pulse travels along the fibre and, if it reaches a boundary, it is totally internally reflected back into the fibre's core, so it does not leave the fibre. This means that the pulse can be detected many kilometres from the source of the signal. The pulse will even travel around curves in the fibre as shown in Figure 5. Optical fibres are also used in an endoscope. This device allows doctors to see deep inside the body. Endoscopes have several optical fibres bound together in a bundle so that light can travel into and out of the body. White light is sent along one fibre into the body and then reflects off the internal organs and into a bundle of organised fibres. It travels down these fibres back to the outside of the body. The external end of the endoscope is connected to a camera, so the surgeon can see an image of the internal organs as they operate. The endoscope can be inserted down the oesophagus or trachea to see into the stomach or lungs. Alternatively, the surgeon can cut small holes in the body so they can see, and operate on, other internal organs. Endoscopes can have small tools fitted to their ends, such as tiny tweezers which can take tissue samples. They can also transmit very intense laser light allowing surgeons to make cuts or cauterise wounds inside the body. Endoscopes are not only used in medicine. Similar devices are used by plumbers to investigate blocked drainpipes or by builders to look under floorboards. Optical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage in fiber-optic communications, where they permit transmission over longer distances and at higher bandwidths (data rates) than wire cables. Endoscopes use optical fibres to produce an image of inside the body. A doctor can insert a bundle of optical fibres into the body. Some carry light into the body, and some carry light reflected off internal body surfaces back out. Fiber is preferred over electrical cabling when high bandwidth, long distance, or immunity to electromagnetic interference is required. This type of communication can transmit voice, video, and telemetry through local area networks or across long distances. Fiber optics (optical fibers) are long, thin strands of very pure glass about the size of a human hair. They are arranged in bundles called optical cables and used to transmit signals over long distances. Fiber optic data transmission systems send information over fiber by turning electronic signals into light. Optical fiber communication use the near -infrared spectral band ranging from nominally 770 to 1675 nm. Electromagnetic energy is a combination of electrical and magnetic fields and includes power, radio waves, microwaves, infraredlight, visible light, ultraviolet light, x-rays, and gamma rays
Distinguish between transverse and longitudinal waves and give suitable examples.
Transverse waves: transverse wave, motion in which all points on a wave oscillate along paths at right angles to the direction of the wave's advance. Transverse waves cause the medium to move perpendicular to the direction of the wave. A wave in which the particles of medium vibrate up and down at right angle to direction in which wave is moving is called transverse wave. Transverse wave can be produced only in solid and liquids but not in gases. In transverse waves, the oscillations are at right angles to the direction of travel and energy transfer. Longitudinal waves: Longitudinal waves cause the medium to move parallel to the direction of the wave. For a longitudinal wave, the points along the wave vibrate in the same direction that the wave is moving in. a wave vibrating in the direction of propagation. The particles move from left to right; Longitudinal waves are waves in which the motion of the individual particles of the medium is in a direction that is parallel to the direction of energy transport. longitudinal wave, wave consisting of a periodic disturbance or vibration that takes place in the same direction as the advance of the wave. Longitudinal waves are waves in which the motion of the individual particles of the medium is in a direction that is parallel to the direction of energy transport. Longitudinal waves are the waves where the displacement of the medium is in the same direction as the direction of the travel of the wave. The distance between the centres of two consecutive regions of compression or the rarefaction is defined by wavelength, λ. In longitudinal waves, particles of wave move in direction of propagation of waves. In a sound wave, the particles of the medium vibrate back and forth in the same direction of the disturbance. Therefore, sound wave is called a longitudinal wave. Characteristics of Longitudinal Waves. As in the case of transverse waves the following properties can be defined for longitudinal waves: wavelength, amplitude, period, frequency and wave speed. However instead of peaks and troughs, longitudinal waves have compressions and rarefactions. - Rarefractions: Compression is that part of longitudinal wave in which the medium of particles are closer and there is momentary decrease in volume of medium. Rarefaction is that part of longitudinal wave in which the medium of particles apart and there is momentary increase in volume of medium. Physics. compressions are regions of high pressure due to particles being close together. rarefactions are regions of low pressure due to particles being spread further apart. When sound wave travels through a medium, say air, the particles of medium disturb in the same fashion, i.e. compression and rarefaction (depression). When air particles come closer it is called compression.On the other hand, when particles go farther than their normal position it is called rarefaction. A compression is a region in a longitudinal wave where the particles are closest together.A rarefaction is a region in a longitudinal wave where the particles are furthest apart.
State the dangers of ultraviolet radiation, from the Sun or from tanning lamps.
UV rays, either from the sun or from artificial sources like tanning beds, can cause sunburn. Exposure to UV rays can cause premature aging of the skin and signs of sun damage such as wrinkles, leathery skin, liver spots, actinic keratosis, and solar elastosis. UV rays can also cause eye problems. ultraviolet can damage skin cells and lead to skin cancer and damage the eyes, it can cause skin to age prematurely; X-rays damage cells inside the body. Exposure to UV rays can cause premature aging of the skin and signs of sun damage such as wrinkles, leathery skin, liver spots, actinic keratosis, and solar elastosis. UV rays can also cause eye problems. Ultraviolet light in sunlight can cause the skin to tan or burn and can also damage eyes. cause skin to age prematurely; X-rays damage cells inside the body. They cause dangerous ionisation and when this happens with molecules in living cells, the genetic material of a cell, the DNA is damaged. Ultraviolet light is damaging to the skin and eyes. Long, or intense, exposure to the skin can cause burns and, if the skin cells are damaged, lead to skin cancers. The retina at the back of the eye is particularly sensitive and, because we cannot actually tell if something is emitting UV, it is easy to damage the retina during sun tanning.
Describe what is meant by wave motion as illustrated by vibration in ropes and springs and by experiments using water waves.
Wave is a phenomenon or disturbance in which energy is transferred from one point to another without any direct contact between them. Wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium —that is, with little or no associated mass transport. They consist, instead, of oscillations or vibrations around almost fixed locations. There are two basic types of wave motion for mechanical waves: longitudinal waves and transverse waves. The animations below demonstrate both types of wave and illustrate the difference between the motion of the wave and the motion of the particles in the medium through which the wave is travelling. In wave motion, the particles of the medium vibrate about their mean positions. The particles of the medium do not move from one place to another. A wave motion travels at the same speed in all directions in the given medium. The speed of a wave depends upon the nature of the medium through which it travels.
Use the terminology for the angle of incidence i and angle of refraction r and describe the passage of light through parallel-sided transparent material.
When light travels from a less dense material to a more dense material (e.g. from air to glass), the light ray bends towards the normal. That is, the angle of incidence > angle of refraction.When light travels from a more dense material to a less dense material (e.g. from glass to water), the light ray bends away from the normal. That is, the angle of refraction > angle of incidence. When a ray of light passes from one medium to another, it bends. This bending of light is called refraction. the passage of light through parallel-sided transparent material, indicating the angle of incidence i and angle of refraction r. Refraction in a glass block. When light passes from air through a block with parallel sides, it emerges parallel to the path of the light ray that entered it. Refraction explains why an object appears to bend when it goes through water. If light enters any substance with a higher refractive index (such as from air into glass) it slows down. The light bends towards the normal line. If light travels enters into a substance with a lower refractive index (such as from water into air) it speeds up. The light bends away from the normal line. The light bends towards the normal line. If light travels enters into a substance with a lower refractive index (such as from water into air) it speeds up. The light bends away from the normal line. A higher refractive index shows that light will slow down and change direction more as it enters the substance. Refraction occurs when a wave enters a medium of different density, e.g from air to glass. When the wave enters a denser medium as in a the animation from R1 to R2, this property of the medium is called the Refractive Index. The wave length becomes shorter and the wave speed decreases. The density of a material affects the speed that a wave will be transmitted through it. In general, the denser the transparent material, the more slowly light travels through it. Glass is denser than air, so a light ray passing from air into glass slows down. When light travels from a less dense material to a more dense material (e.g. from air to glass), the light ray bends towards the normal. That is, the angle of incidence > angle of refraction. When light travels from a more dense material to a less dense material (e.g. from glass to water), the light ray bends away from the normal. That is, the angle of refraction > angle of incidence. The same thing happens when light hits glass or any other transparent material. Some light is reflected off the object whereas the rest passes through and is refracted. All materials have what is known as an index of refraction, which is linked to how fast light can travel through the material. The refractive index of a transparent material is a fundamental of that material and can be used to identify the material. The ratio of the velocity of light in vacuum to the velocity of light in a medium is referred to as the refractive index of the medium, n. The bending of light as it passes from one medium to another is called refraction. The angle and wavelength at which the light enters a substance and the density of that substance determine how much the light is refracted.
Demonstrate understanding of safety issues regarding the use of microwaves and X-rays.
microwaves cause internal heating of body tissues. infrared radiation is felt as heat and causes skin to burn. X-rays damage cells causing mutations (which may lead to cancer) and cell death - this is why doctors and dentists stand behind protective screens when taking lots of X-rays. Microwave: Microwave radiation can heat body tissue the same way it heats food. Exposure to high levels of microwaves can cause a painful burn. Two areas of the body, the eyes and the testes, are particularly vulnerable to RF heating because there is relatively little blood flow in them to carry away excess heat. Microwave radiation can heat body tissue the same way it heats food. Exposure to high levels of microwaves can cause a painful burn. Two areas of the body, the eyes and the testes, are particularly vulnerable to RF heating because there is relatively little blood flow in them to carry away excess heat. Microwaves are absorbed strongly by some of the molecules present in food and living tissue, causing a heating effect. This effect is used to cook food in microwave ovens (Figure 2). Microwaves are produced by a small transmitter inside the oven. They are absorbed by the food which heats up rapidly. The oven is made of metal so that the microwaves reflect back inside the chamber and heat the food instead of escaping. If the microwaves could escape the oven, they could be harmful to the user as they would cause burns inside the body. X-rays: While X-rays are linked to a slightly increased risk of cancer, there is an extremely low risk of short-term side effects. Exposure to high radiation levels can have a range of effects, such as vomiting, bleeding, fainting, hair loss, and the loss of skin and hair. No patients should wait or change in the x-ray room while another patients are being radiographed. If anyone is required to support a patient or film during x-ray exposure, he/she must wear a lead apron and lead gloves and avoid the direct beam by standing to one side and away from the x-ray tube. X-rays can damage cells, especially those that are still growing, and so they are not used unless they are really needed. They are best avoided during pregnancy. The medical staff using X-rays protect themselves from repeated exposure by leaving the room while X-rays are taken or by standing behind lead sheets.
Use the term wavefront.
wave front - the line joining identical parts of a wave. Circular wave fronts and plane wave fronts are two main types. wave fronts always cross waves at 90 degrees a surface containing points affected in the same way by a wave at a given time. wave front, imaginary surface representing corresponding points of a wave that vibrate in unison. A surface on which the wave disturbance is in same phase at all points is called a wavefront. This is an imaginary surface that we draw to represent the vibrating part of a wave. If you draw semi-circular sound waves spreading out from a speaker, the semi-circular lines are the wavefront. A wavefront is defined as the locus of all points of the medium which vibrate in the same phase. Depending on the shape of the source of light, wavefronts can be of three types. Wavefront is defined as the imaginary surface constructed by the locus of all points of a wave that have the same phase, i.e. have the identical path length from the source of that wave.
Describe the typical properties and use of radiations in all the different regions of the electromagnetic spectrum including:
ー radio and television communications (radio waves) ー satellite television and telephones (microwaves) ー electrical appliances, remote controllers for televisions and intruder alarms (infra-red) ー medicine and security (X-rays). Radio waves: Radio waves are used for communication such as broadcasting television and radio, communications and satellite transmissions. - Radio waves have the longest wavelength and so the lowest frequency of all the electromagnetic waves.They are produced when electrons are moved back and forth inside wires by varying electric currents.This principle is used to construct large radio transmission towers (Figure 1). These towers can produce powerful radio signals which can be detected over great distances. - The signals can be used to send television and radio signals which can travel through the air. Most radio signals are refracted by the upper atmosphere and so can actually travel past the curvature of the Earth to reach distant places. Microwaves: Microwaves are used for cooking food, communications and for satellite communications. Intense sources of microwaves can be dangerous through internal heating of body cells. - Microwaves are similar to radio waves and are also produced by oscillating electrons in wires, but they have a higher frequency. - Microwaves are absorbed strongly by some of the molecules present in food and living tissue, causing a heating effect. This effect is used to cook food in microwave ovens (Figure 2). - Microwaves are produced by a small transmitter inside the oven. They are absorbed by the food which heats up rapidly. The oven is made of metal so that the microwaves reflect back inside the chamber and heat the food instead of escaping. If the microwaves could escape the oven, they could be harmful to the user as they would cause burns inside the body. - Microwaves are also used to transmit signals to satellites in orbit around the Earth. Radio waves cannot easily penetrate the upper atmosphere, but microwaves can and so make satellite communication possible. - Low-power microwaves are used by mobile phones to communicate with signal towers spread throughout towns and cities (Figure 3). As these towers communicate with many phones at once, they produce stronger signals then the phones themselves. This means that staying close to a transmission tower could be harmful, even though using a mobile phone is not. Infra-red radiation: Infrared (IR) light is used by electrical heaters, cookers for cooking food, short-range communications like remote controls, optical fibres, security systems and thermal imaging cameras which detect people in the dark. The heating effect of IR can cause burns to the skin. - Infra-red radiation is emitted by all objects but hotter objects emit more than cold ones. Infra-red cameras can be used to detect the infra-red radiation being emitted from an object and this information is used to produce a picture showing temperature differences.This is useful for medical diagnosis (Figure 4), detecting electronic faults and for finding places where insulation is poor. - Low-power infra-red signals are used in television remote controls. Pressing a button on the remote control produces a signal from a diode which spreads around the room. A sensor in the television detects the signal and changes the channel or increases the volume depending on which signal was detected. As the diode is on the front of the remote control, you usually need to point it towards the television for it to detect the signal. Sometimes, however, you can reflect the signal off walls and it will still be detected. - Infra-red detectors can also be used as part of an intruder alarm. Because people are warm, they emit infra-red radiation and so a person moving around a room will change the amount of infra-red radiation detectable in different parts of the room. A burglar entering a room could be detected by an infra-red detector which would set off an alarm system. Furthermore, the hotter an object, the shorter the wavelength of its peak emission (see figure 1). Recalling that short wavelengths correspond to higher energies, this means that hotter objects give off more high-energy radiation than colder objects—as intuition might suggest. Visible light: Visible light is the light we can see, so is used in photography and illumination. It is also used in fibre optic communications, where coded pulses of light travel through glass fibres from a source to a receiver. - Visible light is simply electromagnetic radiation you can see when it enters your eye. The behaviour of visible light is covered insubtopic Ultraviolet radiation: We cannot see ultraviolet (UV) light but it can have hazardous effects on the human body. Ultraviolet light in sunlight can cause the skin to tan or burn. Fluorescent substances are used in energy-efficient lamps - they absorb ultraviolet light produced inside the lamp, and re-emit the energy as visible light. Similar substances are used on bank notes to detect forgeries. The hazardous properties of UV mean it will kill bacteria and can be used for disinfecting water. - Ultraviolet radiation (UV) is produced by the Sun and some fluorescent tubes. Most of the UV radiation emitted by the sun is absorbed by our atmosphere before it reaches the surface of the Earth but some parts of the UV spectrum can pass through. - Some chemicals can absorb UV radiation and then emit visible light instead. Clothing which has been washed in biological washing powder is a good example. When the clothes are exposed to UV light, they appear to glow and this effect is used in fairgrounds and discos (Figure 5). Some clothes are designed using UV-sensitive dyes to increase this effect. X-rays - X-rays are short wavelength electromagnetic rays which are produced when fast-moving electrons are brought to a sudden stop inside an X-ray tube. - The X-rays produced can pass through some materials easily, such as muscle, but are absorbed by others, like bone. This allows us to take photographs of the bones inside our body. A photographic plate (or X-ray camera) is placed behind the patient's body and then the patient is exposed to a burst of X-rays. The areas where there is only muscle or skin allow the X-rays to pass through but the areas with bone block some of the X-rays. These X-rays are detected by the photographic film, making the areas with soft tissue dark but leaving the areas with bone white. Doctors can then examine the images to find breaks in bone (Figure 7). - X-rays are also used for security at airports and other venues. Luggage passes through an X-ray device and the image is used to check for the presence of any dangerous or banned materials. Gamma rays - Gamma rays have very similar properties and effects to X-rays but their origin is different. Gamma rays are produced during the radioactive decay of a nucleus. To produce strong gamma rays, samples of radioactive material, such as strontium-90, are collected together. - Gamma rays can be very dangerous. They can kill living cells or damage the DNA inside the cells, leading to cancer. However, this cell-damaging effect can also be used to destroy cancerous cells. A beam of concentrated gamma rays can be directed at the cancerous cells killing them in a treatment known as radiotherapy
Describe how waves can undergo:
ー reflection at a plane surface: Reflection of a plane wave using Huygens Principle. As discussed earlier, when light is incident on the surface it is re- emitted without any change in the frequency. This re-emitted light which is returned into the same medium from which it comes out is called Reflection of Light. An incident ray of light hits a plane mirror at an angle and is reflected back off it. The angle of reflection is equal to the angle of incidence. Both angles are measured from the normal. The normal is an imaginary line at right angles to the plane mirror. Waves reflect from surfaces. The angle of incidence equals the angle of reflection . This is called the law of reflection. So, if a wave hits a mirror at an angle of 36°, it will be reflected at the same angle (36°). ー refraction due to a change of speed.When sound waves move from one medium to another, there will be changes to the velocity (or speed), frequency and wavelength of the sound wave. This change in velocity can also result in a change of direction of the sound wave - also known as refraction. Refraction happens because the speed of the wave changes. Light travels slower (compared to its speed in air) in a more dense material like glass. The wavelength will also decrease in order to keep the frequency constant. Water waves travel slower in shallower water. Although the wave slows down, its frequency remains the same, due to the fact that its wavelength is shorter. When waves travel from one medium to another the frequency never changes. The wavelength of a wave does not affect the speed at which the wave travels. Both Wave C and Wave D travel at the same speed. The speed of a wave is only altered by alterations in the properties of the medium through which it travels. When a wave is transmitted through a medium with a change in density at a boundary, this change in density causes refraction of the wave to occur, where the wave effectively changes direction due to the change in density causing a change in speed of the wave. Waves change speed when they pass across the boundary between two different substances, such as light waves refracting when they pass from air to glass. This causes them to change direction and this effect is called refraction.