Physics Midterm Exam Review
Why do mountains look blue from a distance
"The haze which appears to surround any distant object is due to an optical phenomenon called 'Rayleigh scattering'. This effect, first investigated theoretically by Lord Rayleigh, causes the rays of light which impinge on small particles to be scattered in various directions... Since the atmosphere is always laden with small dust particles, water droplets and the like and since even the air molecules themselves contributed to some extent to the scattering... if an observer look sat a distant object with the intervening atmosphere illuminated by sunlight, eyes will receive the blue scattered rays of sunlight to reflect the object itself. Therefore any distant object will always appear to display"
Transverse wave
A wave vibration at right angles to the direction the wave is traveling
Blue Shift
An increase in the measured frequency of light from an approaching source
Node
Any part of a standing wave that remains stationary
Amplitude
The distance from the midpoint to the maximum (crest) of wave, or equivalently, from the midpoint to the minimum (trough)
Wavelength
The distance from the top of the crest of a wave to the top of the following crest, or equivalently, the distance successive identical parts of the wave
What determines whether a material is transparent or opaque?
The resonant frequency of the electrons in the material. If the frequency of the light is the same as the resonant frequency of the electrons, the material is opaque.
Ultrasonic and infrasonic
Though all three ends with the suffix 'sonic' only infra sonic and ultra sonic are related to the frequency of the sound. Infrasonic is sound with less than 20 hertz and ultrasonic is are more than 20000 hertz. The other sonic i.e., supersonic is not related to the frequency but to the velocity of sound. Sound travels approximately at 330m/s. at STP. If any object travels at more than the speed of the sound then we say that object is travelling at supersonic. Super sonic jets are said to travel at speeds greater than sound and may send shock waves. Concorde is one such plane which is suspended now due its noise and shock waves.
Wave
A " wiggle in space and time"; A disturbance that repeats regularly in space and time that is transmitted progressively from one place to the next with no actual transport of matter
Shock wave
A cone shaped waves produced by an object moving at supersonic speed trough a liquid
Sine Curve
A curve whose shape represents the crest and trough of a wave, as traced out by a swinging pendulum that drops a trail of sand over a moving conveyor belt
Red shift
A decrease in the measure of light from a receding source
Interference Pattern
A pattern formed by the overlapping of two or more waves that arrive in a region at the same time
Transverse wave
A transverse wave is a moving wave that consists of oscillations occurring perpendicular (or right angled) to the direction of energy transfer. If a transverse wave is moving in the positive x-direction, its oscillations are in up and down directions that lie in the y-z plane. Light is an example of a transverse wave.
Longitudinal Wave
A wave in which the vibration is in the same direction as that in which the wave is traveling, rather than at right angles to it
Constructive Interference
Addition of two or more waves when wave crests overlap to produce a resulting wave of increased amplitude
Vibration
An oscillation or repeating back- and-forth motion, about an equilibrium position
Why are sunsets red
As the path that sunlight takes through our atmosphere increases in length, ROYGBIV encounters more and more atmospheric particles. This results in the scattering of greater and greater amounts of yellow light. During sunset hours, the light passing through our atmosphere to our eyes tends to be most concentrated with red and orange frequencies of light. For this reason, the sunsets have a reddish-orange hue. The effect of a red sunset becomes more pronounced if the atmosphere contains more and more particles. The presence of sulfur aerosols (emitted as an industrial pollutant and by volcanic activity) in our atmosphere contributes to some magnificent sunsets (and some very serious environmental problems).
Destructive Inference
Combination of waves where crests of one wave overlap troughs of another, resulting in a wave of decreased amplitude
Simple harmonic motion
In mechanics and physics, simple harmonic motion is a type of periodic motion where the restoring force is directly proportional to the displacement. It can serve as a mathematical model of a variety of motions, such as the oscillation of a spring. In addition, other phenomena can be approximated by simple harmonic motion, including the motion of a simple pendulum as well as molecular vibration. Simple harmonic motion is typified by the motion of a mass on a spring when it is subject to the linear elastic restoring force given by Hooke's Law. The motion is sinusoidal in time and demonstrates a single resonant frequency. In order for simple harmonic motion to take place, the net force of the object at the end of the pendulum must be proportional to the displacement.
Standing Waves
In physics, a standing wave - also known as a stationary wave - is a wave that remains in a constant position. This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling in opposite directions. In the second case, for waves of equal amplitude traveling in opposing directions, there is on average no net propagation of energy. In a resonator, standing waves occur during the phenomenon known as resonance.
Wave speed
In the case of a wave, the speed is the distance traveled by a given point on the wave (such as a crest) in a given interval of time. In equation form, If the crest of an ocean wave moves a distance of 20 meters in 10 seconds, then the speed of the ocean wave is 2.0 m/s.
Inertial property
Inertial properties are those properties related to the material's tendency to be sluggish to changes in its state of motion. The density of a medium is an example of an inertial property. The greater the inertia (i.e., mass density) of individual particles of the medium, the less responsive they will be to the interactions between neighboring particles and the slower that the wave will be. As stated above, sound waves travel faster in solids than they do in liquids than they do in gases. However, within a single phase of matter, the inertial property of density tends to be the property that has a greatest impact upon the speed of sound. A sound wave will travel faster in a less dense material than a more dense material. Thus, a sound wave will travel nearly three times faster in Helium than it will in air. This is mostly due to the lower mass of Helium particles as compared to air particles.
When you are looking at a distant galaxy through a telescope, how is it that you are looking back in time?
It takes many years for the light from the galaxy to reach Earth. We see the galaxy as it was when the light left it.
Longitudinal waves
Longitudinal waves, also known as "l-waves", are waves in which the displacement of the medium is in the same direction as, or the opposite direction to, the direction of travel of the wave.
The Suns color
Meanwhile, the light that is not scattered is able to pass through our atmosphere and reach our eyes in a rather non-interrupted path. The lower frequencies of sunlight (ROY) tend to reach our eyes as we sight directly at the sun during midday. While sunlight consists of the entire range of frequencies of visible light, not all frequencies are equally intense. In fact, sunlight tends to be most rich with yellow light frequencies. For these reasons, the sun appears yellow during midday due to the direct passage of dominant amounts of yellow frequencies through our atmosphere and to our eyes.The appearance of the sun changes with the time of day. While it may be yellow during midday, it is often found to gradually turn color as it approaches sunset. This can be explained by light scattering. As the sun approaches the horizon line, sunlight must traverse a greater distance through our atmosphere; this is demonstrated in the diagram below.
Crest
One of the places in a wave where the wave is highest or the disturbance is greatest
Trough
One of the places where the wave is lowest, disturbance is greatest , in the opposite direction from a crest
Simple harmonic motion
Periodic motion which acceleration proportional to the distance from in the equilibrium position is directed toward that equilibrium position
Why are plants green
Plants are green because of the chloroplasts inside them. These are the tiny organelles used by the plant to carry out the process of photosynthesis. Chloroplasts are green; therefore, plants are green. Of course, the question then becomes: why are these chloroplasts green? The answer is chlorophyll--the pigment inside the chloroplasts. It absorbs red and blue light from the sun and uses this light to carry out photosynthesis within the plant. After discovering that chlorophyll is the initial reason behind the green color, we must then question why chlorophyll itself is green, as opposed to blue or orange or any other color across the spectrum. To answer this question, we have to delve into the science behind pigments. Pigments absorb light. This is their function. We have established that chlorophyll absorbs red and blue light. So why, then, does it make the plant green? This is because a pigment becomes the color it does not absorb. In the true light spectrum, there is only red, green and blue. Chlorophyll absorbs the red and blue, and reflects the green. Thus, the plant appears green.
Speed of sound
Sound is faster in wet air than dry air. Sound is nothing but vibration of air so in the presence of water in the air(moist air) the water droplet comes in contact with the vibration and amplifys it because velocity of sound is higher in water than in air(amplification is only possible when sound touches the substance in which sound's speed is much higher than air)so amplified sound is created in moist air with higher velocity and obviously in the absence of water droplet or in dry air no amplification is possible and speed remains as it should be in air
In Phase
Term applied to two or more waves whose crests and troughs arrive at a place at the same time, so that their effects reinforce each other
Out of phase
Term applied to two waves from which the crest of one wave arrives at a point at the same time trough of the second waves when arrives.There effects cancel each other
Doppler Effect
The Doppler effect (or Doppler shift) is the change in frequency of a wave (or other periodic event) for an observer moving relative to its source. It is named after the Austrian physicist Christian Doppler, who proposed it in 1842 in Prague. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession. When the source of the waves is moving toward the observer, each successive wave crest is emitted from a position closer to the observer than the previous wave. Therefore, each wave takes slightly less time to reach the observer than the previous wave. Hence, the time between the arrival of successive wave crests at the observer is reduced, causing an increase in the frequency. While they are travelling, the distance between successive wave fronts is reduced, so the waves "bunch together". Conversely, if the source of waves is moving away from the observer, each wave is emitted from a position farther from the observer than the previous wave, so the arrival time between successive waves is increased, reducing the frequency. The distance between successive wave fronts is then increased, so the waves "spread out". For waves that propagate in a medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. The total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analyzed separately. For waves which do not require a medium, such as light or gravity in general relativity, only the relative difference in velocity between the observer and the source needs to be considered.
Elastic property
The Doppler effect (or Doppler shift) is the change in frequency of a wave (or other periodic event) for an observer moving relative to its source. It is named after the Austrian physicist Christian Doppler, who proposed it in 1842 in Prague. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession. When the source of the waves is moving toward the observer, each successive wave crest is emitted from a position closer to the observer than the previous wave. Therefore, each wave takes slightly less time to reach the observer than the previous wave. Hence, the time between the arrival of successive wave crests at the observer is reduced, causing an increase in the frequency. While they are travelling, the distance between successive wave fronts is reduced, so the waves "bunch together". Conversely, if the source of waves is moving away from the observer, each wave is emitted from a position farther from the observer than the previous wave, so the arrival time between successive waves is increased, reducing the frequency. The distance between successive wave fronts is then increased, so the waves "spread out". For waves that propagate in a medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. The total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analyzed separately. For waves which do not require a medium, such as light or gravity in general relativity, only the relative difference in velocity between the observer and the source needs to be considered.
Hertz
The SI unit of frequency. One hertz (Hz) is one vibration per second
Bow Wave
The V-shaped wave produced by an object moving on a liquid surface faster than the wave speed
Doppler Effect
The change in frequency of a wave due to the motion of the source of the receiver
Why is the sky blue
The interaction of sunlight with matter can result in one of three wave behaviors: absorption, transmission, and reflection. The atmosphere is a gaseous sea that contains a variety of types of particles; the two most common types of matter present in the atmosphere are gaseous nitrogen and oxygen. These particles are most effective in scattering the higher frequency and shorter wavelength portions of the visible light spectrum. This scattering process involves the absorption of a light wave by an atom followed by reemission of a light wave in a variety of directions. The amount of multidirectional scattering that occurs is dependent upon the frequency of the light. (In fact, it varies according to f4.) Atmospheric nitrogen and oxygen scatter violet light most easily, followed by blue light, green light, etc. So as white light (ROYGBIV) from the sun passes through our atmosphere, the high frequencies (BIV) become scattered by atmospheric particles while the lower frequencies (ROY) are most likely to pass through the atmosphere without a significant alteration in their direction. This scattering of the higher frequencies of light illuminates the skies with light on the BIV end of the visible spectrum. Compared to blue light, violet light is most easily scattered by atmospheric particles. However, our eyes are more sensitive to light with blue frequencies. Thus, we view the skies as being blue in color.
Frequency
The number of events per time; measured in hertz. Inverse of period
Why is the ocean blue
The ocean is blue because of the way it absorbs sunlight, according to the National Oceanic and Atmospheric Administration (NOAA). When sunlight hits the ocean, the water strongly absorbs long-wavelength colors at the red end of the light spectrum, as well as short-wavelength light, including violet and ultraviolet. The remaining light that we see is mostly made up of blue wavelengths.However, NOAA notes that the ocean may take on other hues, including red and green, if light bounces off objects floating near the surface of the water, such as sediment and algae. Just how blue the water is depends on how much of it is available to absorb the light. For instance, water in a glass is clear — there aren't enough water molecules to really absorb the light. But ocean water appears bluer the farther you travel down the water column. The water molecules absorb infrared, red and ultraviolet light first, and then yellow, green and violet. Blue light is absorbed the least, giving it the greatest ocean penetration depth, according to NASA. This fact is clear if you look at unedited underwater photos that weren't taken with a camera flash or another artificial light source — even the most vibrant of tropical fish look blue.
Antinode
The positions on a standing wave where the largest amplitudes occur
Sonic boom
The sharp crack heard when the shock wave that sweeps behind a supersonic aircraft reaches the listener
Period
The time required for a pendulum to make one to-and fro swing. In general, the time required to complete one single cycle
You can get a sunburn on a cloudy day, but you can't get a sunburn even on a sunny day if you are behind glass. Explain.
The ultraviolet photons that give you a sunburn, pass right through the water vapor in the clouds but they are absorbed by glass.
Standing wave
Wave in which parts of the wave remains stationary and the wave appears not to be traveling. The result interference between and incident wave and reflected wave
Interference
Wave interference is the phenomenon that occurs when two waves meet while traveling along the same medium. The interference of waves causes the medium to take on a shape that results from the net effect of the two individual waves upon the particles of the medium. To begin our exploration of wave interference, consider two pulses of the same amplitude traveling in different directions along the same medium. Let's suppose that each displaced upward 1 unit at its crest and has the shape of a sine wave. As the sine pulses move towards each other, there will eventually be a moment in time when they are completely overlapped. At that moment, the resulting shape of the medium would be an upward displaced sine pulse with an amplitude of 2 units.
Why are metals shiny
Yes, shiny materials are good reflectors of visible light, one of many kinds of radiation. They may not be such good reflectors of other kinds of radiation, like x-rays, for example, which are just like light except they have higher frequencies. Many different kinds of metal are shiny. Gold is a metal which stays shiny for a long time because it does not react much chemically with the air. Silver is shinier, but tarnishes easily. Many other metals, like iron or steel, aluminum, and copper are also shiny. What makes them that way is that some of the electrons in these metals can move around very very easily. Electrons feel pushes and pulls when an electric field comes along. Light waves are made up of electric and magnetic fields. When a light wave hits a metallic surface, the electrons on the surface are pushed and pulled by the field of the incoming wave. How far do they go? They slosh around until the field that they create (after all, electrons are charged and they make their own field) cancels out the incoming field exactly. They stop when the net force is zero on them. This means that the electric field inside a conducting metal is zero. If an incoming wave hits the material, and the electric field is zero on a plane surface at all times, you can express this as a sum of two waves -- one coming in, and an equal and opposite one coming out. The sloshing electrons in the metal radiate a wave going out that exactly matches the one coming in. If there is some resistivity to the metal, or some corrosion, the metal becomes less shiny. There's another way a material can be shiny. If a material is transparent, but has a different index of refraction than the air, then light rays will bend when they strike the surface of the material. Some, but not all, will also be reflected from the surface at the same angle of reflection as if the material had been made out of metal. If the light starts out in the dense material (like water or glass) and hits the surface with air, if the angle is steep enough so that the law of refraction cannot be satisfied, then all of the light will bounce back into the water or glass, in a process called "total internal reflection", making that surface look shiny too.
