Unit Three: Waves

Broadcasting radio waves

The modified carrier wave is converted from an electric signal to a radio wave by using an antenna, like the one in Figure 20. The electric signal causes electrons in the antenna to vibrate. These vibrating electrons create electromagnetic waves that travel outward from the antenna in all directions. The signal from the radio station is strongest closer to the broadcasting antenna and becomes weaker as you move away. Eventually, the signal will be too weak to be detected by your radio. This is why radios in New York City do not pick up FM radio stations broadcast in Los Angeles. Bad weather, surrounding mountains, and artificial structures can also interfere with radio transmissions.

Frequency of electromagnetic wave is

The number of vibration per second (Hz)

Wave

A repeating disturbance that transfers energy through matter or space

Matter and Electromagnetic Waves

All matter contains charged particles that are always in motion. As a result, all objects emit electromagnetic waves. Objects can emit electromagnetic waves at many wavelengths. However, the dominant wavelength emitted becomes shorter as the temperature of the material increases.

The parts of a wave (Transverse)

Crest: The high points of a transverse wave. Troughs: Low points of a transverse wave. The imaginary line that is half the vertical distance between a crest and a trough is the rest position.

What is the Carrier Wave

Each radio station is assigned a particular radio frequency for their broad casts- this specific frequency is a carrier wave

Pitch is the human perception of a waves

Frequency

Calculating Wave speed (m/s)

Frequency (Hz) x Wavelength f= fy

Medium

Matter through which a wave travels

What is the electromagnetic spectrum

The entire range of electromagnetic wave frequencies.

1) A wave traveling in water has a frequency of 250 Hz and a wavelength of 6.0 m. What is the speed of the wave? 2) The lowest-pitched sounds humans can generally hear have a frequency of roughly 20 Hz. What is the approximate wavelength of these sound waves if their wave speed is 340 m/s? 3) A particular radio station broadcasts radio waves at 100 MHz (100 million Hz). If radio waves travel at the speed of light (300 million m/s), then what is the wavelength of the radio waves that the station is broadcasting? 4) Challenge A sound wave with a frequency of 100.0 Hz travels in water with a speed of 1,500 m/s and then travels in air with a speed of 340 m/s. Approximately how many times larger is the wavelength in water than in air?

1) 2) 3) 4)

1. MAIN Idea Infer Would a vibrating proton produce an electromagnetic wave? Would a vibrating neutron? Explain. 2. Compare the frequency of an electromagnetic wave with the frequency of the vibrating charge that produces the wave. 3. Describe how electromagnetic waves transfer energy to matter. 4. Explain how an electromagnetic wave can travel through space that contains no matter. 5. Think Critically Would a stationary electron produce an electromagnetic wave? Would a stationary magnet? Explain.

1) Proton yes, because it is a charged particle; Neutron no, because it is not a charge particle 2) They are equal 3) by causing charged particles within objects to move 4) An electromagnetic wave is made of vibrating electric and magnetic fields that continually induce each other; matter is not needed for this to occur. 5) No; No; they have to move to produce a wave.

1. MAIN Idea Describe the motion of an unanchored rowboat when a water wave passes. Does the wave move the boat forward? 2. Contrast how you would move a spring to make a transverse wave with how you would move a spring to make a longitudinal wave. 3. Identify evidence that seismic waves transfer energy without transferring matter. 4. Identify a mechanical wave that is also a longitudinal wave. 5. Think Critically Describe how the world would be different if all waves were mechanical waves. 6. Calculate Time The average speed of sound in water is 1,500 m/s. How long would it take a sound wave to travel 9,000 m in water?

1) The boat will move up and down because of the waves but it will not move forward because the wave doesn't carry the boat with it 2) To make the transverse wave, I would have one person hold one end of the spring and on the other end I would move it up and down. To make the longitudinal wave, I would squeeze the coils together at one end and then let go of them while still holding onto the coils at the end 3) Seismic waves and cause great change. Tidal waves and direct damage to building and other structures are caused by earthquakes. However, the waves move through Rock and soil. Rock and soil are not carried along with the waves. 4) Sound 5) If all waves were mechanical waves then light waves would not be able to travel through the vacuum of space. The energy from the Sun would have no way to reach the Earth. As a result, Earth would be very cold and dark. 6) t = d/s t = 9,000/1,500 t = 6 seconds

1. MAIN Idea Explain how sound travels from your vocal cords to your friend's ears when you talk. 2. Summarize the physical reasons that sound waves travel at different speeds through different mediums. 3. Explain why sound speeds up when temperature increases. 4. Describe each section of the human ear and its role in hearing. 5. Think Critically Some people hear ringing in their ears, called tinnitus, even in the absence of sound. Form a hypothesis to explain why this occurs.

1) Your vocal cords vibrate and then travel through the air to your friends ear. 2) different temperatures, density, and elasticity change the speed of sound waves 3) particles increase in speed when temperature increases 4) The purpose of the outer ear is to Gather energy in the form of sound waves. The purpose of the inner ear is to Covert sound vibrations to electrical impulses The purpose of the middle ear is to Amplify vibrations from sound waves and transfer them to the cochlea. 5) Well, when the ear cells die, like any other kind of life, energy is dissipated . So since so many ear cells are needed to hear, the many that die at once give off the energy as an audible energy.

1. MAIN Idea Describe two ways that you could direct a light wave around a corner. 2. Predict how rubbing a mirror with sandpaper will affect how the mirror reflects light. 3. Identify what an object's index of refraction indicates. 4. Explain what happens to white light when it passes through a prism. 5. Think Critically Decide whether the lens of your eye, your fingernails, your skin, and your tooth are opaque, translucent, or transparent. Explain. 6) Find an Angle A light ray strikes a mirror at an angle of 42° from the surface of the mirror. What angle does the reflected ray make with the normal? 7. Find an Angle A ray of light hits a mirror at 27° from the normal. What is the angle between the reflected ray and the normal?

1) use mirrors to change light direction, use glass, plastic or other clear substances to refract light around a corner 2) It would make the surface rougher so it would produce a diffuse reflection. 3) it indicates how much light will slow down in the material compared to its speed in a vacuum 4) the white light get refracted at different amounts because of its wavelength and get separated into a rainbow 5) lens is transparent because light passes through without scattering. Fingernails and skin are translucent because light passes through them but you cannot see through them. Teeth are opaque because light doesn't pass through them. 6) 48° 7) 27

11. MAIN Idea Identify a wave that speeds up when it passes from air to water as well as one that slows down. 12. Describe the difference between a longitudinal wave with a large amplitude and one with a small amplitude. 13. Describe how the wavelength of a wave changes if the wave slows down but its frequency does not change. 14. Explain how the frequency of a wave changes when the period of the wave increases. 15. Think Critically You make a transverse wave by shaking the end of a long rope up and down. Explain how you would shake the end of the rope to make the wavelength shorter. 16. Calculate the frequency of a water wave that has a wavelength of 0.5 m and a speed of 4 m/s. 17. Calculate Speed An FM radio station broadcasts radio waves with a frequency of 96,000,000 Hz. What is the speed of these radio waves if they have a wavelength of 3.1 m?

11) A sound wave speeds up as it passes from air to water. A light wave slows down as it passes from air to water. 12) Large Amplitude = More energy Small Amplitude = Less energy 13) If the wave slows down with no change in frequency, the wavelength decreases. 14) The frequency of a wave decreases when the period of the wave increases. 15) To make the wavelength shorter, you would increase the frequency of shakes. 16) Speed = (wavelength)(frequency) Speed = (3.1)(96,000,000) Speed = 297,600,000m/s

14. MAIN Idea Identify and describe the steps that a radio station uses to broadcast sounds to your radio receiver . 15. Explain the difference between AM and FM radio. Make a sketch of how a carrier wave is modulated in AM and FM radio signals. 16. Describe what happens to your signal when you are talking on a cell phone and you travel from one cell to another cell. 17. Explain some of the uses of the Global Positioning System. Why might emergency vehicles be equipped with GPS receivers? 18. Think Critically Why do cordless telephones stop working when you move too far from the base unit?

14) Sound is converted into a signal. signal causes electrons in antenna to vibrate. Vibrating electrons produce electromagnetic (EM) wave. EM wave causes electrons in your antenna to vibrate. Radio turn vibrating electrons into sound. 15) AM radio modulates amplitude. FM radio modulates frequency 16) A central controller transfers your signal to the base station in the new cell. 17) GPS is used by hikers, airplanes, ships, cars, and others to identify their location on Earth. Emergency vehicles have GPS to help them find places quickly. 18) The signal decreases with distance and the signal becomes too weak.

15. MAIN Idea Compare and contrast the two main types of bulbs found in your home. Explain how they produce light. 16. Discuss the advantages of using a fluorescent bulb instead of an incandescent bulb. 17. Describe the difference between coherent and incoherent light. 18. Describe the processes used to produce light in a laser. 19. Identify several uses of lasers. 20. Think Critically Which type of lighting device would you use for each of the following needs: an economical light source in a manufacturing plant, an eye-catching sign that will be visible at night, and a baseball stadium? Explain. 21. Calculate Efficiency A 25-W fluorescent light emits 5.0 J of thermal energy each second. What is the efficiency of the fluorescent light? 22. Use Percentages If 90 percent of the energy emitted by an incandescent bulb is thermal energy, how much thermal energy is emitted by a 60-W bulb each second?

15) incandescent: heats a tungsten filament until it glows fluorescent: electrons collide with gas atoms, UV light is emitted, the phosphors convert UV light to visible light 16) fluorescent bulbs last longer and waste less energy 17) coherent light: one wavelength; one direction; constant distant between crests incoherent light: many wavelengths, many directions, varying distance between crests 18) Atoms in the laser tube absorb light from a flash tube and emit light at one wavelength. Some light waves are reflected between two mirrors and cause more atoms to emit light, resulting in a narrow, intense light beam. 19) read CDs, surgery, light shows, pointers 20) Eradiant = Ein - Ethermal Efficiency = Eout/Ein The correct answer is: 80% 21) 54 J

MAIN Idea Compare and contrast music and noise. 15. Explain how two instruments could be used to produce a pulsing sound, and identify the name for this pulsing sound. 16. Explain how a flute, a violin, and a kettledrum each produce sound. 17. Think Critically Two musical notes have the same pitch and volume. However, they sound very different from each other. How is this possible? 18. Calculate Frequencies A string on a guitar vibrates with a frequency of 440 Hz. Two beats per second are heard when this string and a string on another guitar are played at the same time. What are the possible frequencies of vibration of the second string?

15) pulsing happens when two instruments are close to the same pitch and is called beats. 16) The flute vibrates air in a column. A violin vibrates a string. A kettle drum vibrates a membrane. 17) The two notes have different sound qualities. 18) 438 Hz or 442 Hz

18. MAIN Idea Describe the path that light waves take when you see your image in a mirror. 19. Compare the loudness of sound waves that constructively interfere with the loudness of sound waves that destructively interfere. 20. Describe how one tuning fork's vibrations can cause another tuning fork to vibrate. 21. Infer Sound waves often bend around columns in large concert halls. Is this a result of refraction or diffraction? 22. Think Critically Suppose the speed of light was greater in water than in air. Draw a diagram to show whether an object under water would seem deeper or closer to the surface than it actually is. 23. Calculate Angle of Incidence The angle between a flashlight beam that strikes a mirror and the reflected beam is 80 degrees. What is the angle of incidence?

18) Light waves travel from a light source where some of them reflect off you. Some of those light waves that travel to the mirror where they reflect off the mirror. Some of these light waves then travel from the mirror to your eye. 19) Sound waves will be louder where they constructively interfere and softer whey they destructively interfere. 20) This can occur if both tuning forks are tuned to the same frequency, so they both have the same natural frequency. The vibrations of one tuning fork will cause the air around the other tuning fork to vibrate at the natural frequency of both tuning forks. The second tuning fork will absorb this energy and start to vibrate. This is called resonance. 21) Diffraction 23) 80 degrees

19. MAIN Idea Describe at least three different ways that people use sound. 20. Describe some differences between a gym and a concert hall that might affect the amount of reverberation in each. 21. Compare and contrast echolocation and sonar. 22. Explain how ultrasonic imaging works. 23. Think Critically How might sonar technology be useful in locating deposits of oil and minerals? . 24. Calculate Distance Sound travels at about 1,500 m/s in seawater.How far will a sonar pulse travel in 46 s? 25. Calculate Time How long will it take for an undersea sonar pulse to travel 3 km?

19) to locate objects under water, to diagnose problems, to treat medical ailments 20) Concert halls usually have soft features and are designed for musical enjoyment. Gyms are usually hard and have sharp angles. 21) Both are used to locate objects. Ecolocation is based on living things. Sonar relies in mechanical equipment. 22) Ultrasound is directed toward an object. The sound ways reflect off the target and are used to produce an electronic signal. A computer converts the signals into images call sonograms 23) Sound waves could be reflected from the oil. They would also travel at different speeds through different materials 24) 69 km 25) . 2s

23. MAIN Idea Discuss how optical fibers are used to transmit telephone conversations. 24. Contrast polarized and unpolarized light. 25. Describe how a hologram is made. 26. Identify all the conditions that are necessary for total internal reflection to occur. 27. Think Critically On a sunny day, you are looking at the surface of a lake through polarized sunglasses. How could you use your sunglasses to tell if the light reflected from the lake is polarized? 28. Calculate Number of Fibers An optical fiber has a diameter of 0.3 mm. How many fibers would be needed to form a cable with a square cross section, if the cross section was 1.5 cm on a side?

23). Sounds are converted into an electric signal. The signal is then converted into pulses of light. Those pulses travel through fiber optic cable, and converted back into electrical signals, and then converted back into sound 24) For polarized light, the magnetic fields can vibrate in one direction. For unpolarized light, the magnetic fields can vibrate in any direction. 25) An object is illuminated with a laser. The reflected light interferes with another beam of laser light. This interference is recorded on photographic film. When a laser shines on the film, a hologram is produced. 26) It must occur at a boundary between two materials. Light must travel slower in the present material than in the other material. The angle of incidence must be greater than the critical angle. 27) Tilt you head sideways; rotate the lenses by 90°. If the lake appears noticeably darker or brighter, then the light reflected from the lake is polarized. 28) 2,500

7) Compare and contrast the properties and uses of radio waves, infrared waves, and ultraviolet rays. 8. Explain A mug of tea is heated in a microwave oven. Explain why the tea gets hotter than the mug. 9. Identify the beneficial effects and the harmful effects of human exposure to ultraviolet rays. 10. Name three objects in a home that produce electromagnetic waves, and describe how the electromagnetic waves are used. 11. Think Critically How could infrared imaging be used to find a lost hiker?

7) All are electromagnetic waves; radio waves are very long & are used for communications; Infrared waves are long and are used for thermal imaging; Ultraviolet waves are short and are used for purification & forensic 8) water (tea) absorbs more energy (microwaves) than ceramics (mug) so it gets hotter 9) Beneficial - Purification & vitamin D production; Harmful - damage proteins, DNA molecules, skin, & cause cancer. 10) remote controls use infrared rays; microwaves cook our food; Lights give us light 11) When you scan the area the hiker's body would appear as a warm dot, unless dead.

8. MAIN Idea Explain why a white fence appears to be white. In your answer, include the colors of light that your eye detects and tell how your brain interprets those colors. 9. Identify what color would be seen if equal amounts of red light and green light were mixed. 10. Compare and contrast the primary colors of light and the primary pigment colors. 11. Describe how your eyes detect color. 12. Think Critically Light reflected from an object passes through a green filter, then a red filter, and finally a blue filter. What color will the object appear to be? 13. Use Percentages In the human eye, there are about 120,000,000 rods. If 90,000,000 rods trigger at once, what percent of the total number of rods are triggered? 14. Convert Units The wavelengths of a color are measured in nanometers (nm), which is 0.000000001 meters (one-billionth of a meter). Find the wavelength in meters of a light wave that has a wavelength of 690 nm.

8) White fences reflect all colors. Your eye sees three colors and all three get activated. The brain interprets this as white light 9) yellow 10) Primary colors are red, green, & blue. Primary pigments are magenta, yellow, & cyan. Equally mix primary colors and you get white. Equally mix the primary pigments and you get black. 11) Cones in your retina detect light of specific wave lengths, which your brain detects as colors. Red cones detect red & yellow light, green cones detect yellow and green light, blue cones detect blue & violet light. 12) black 13) 75% 14) 0.000,000,69 nm

8) Determine which will change if you turn up a radio's volume: wave velocity, intensity, pitch, frequency, wavelength, loudness. Explain. 9. Identify the range of human hearing in decibels and the level at which sound can damage human ears. 10. Compare and contrast frequency and pitch. 11. Draw and label a diagram that explains the Doppler effect. 12. Think Critically Why would a passing car exhibit a greater sound frequency change when it moves at 30 m/s than when it moves at 12 m/s?

8) intensity, loudness The higher the intensity and amplitude, the louder the sound, so when you turn up the volume, Intensity and amplitude increases. 9) Noise levels are measured in Decibles. The higher the decibel level, the louder the noise. Sound that are louder than 85 dB can cause permanent hearing loss. 10) Frequency is the number of times a vibration occurs each second. Pitch is the human perception of how high or low a sound is and depends primarily on frequency. The higher the frequency the higher the pitch. 11) 12) The velocity change would be greater so the frequency change would be greater

Amplitude

A measure of energy in a wave. The more energy a wave carries= greater amplitude Distance from crest or trough to normal postion in transverse waves. The deeper the compression, the larger the amlitude of the compression The measure of the size of the disturbance from a wave. If the wave's amplitude is greater, then the disturbance from the wave is also greater. Measured differently for longitudinal and transverse waves. Longitudinal Waves: Is related to how tightly the medium is pushed together at the compressions and how much the medium is pulled apart at the rarefactions. The more tightly the medium is at the compressions, the larger the wave's amplitude is. Another indicator of high amplitude is whether the medium is stretched out more in the rarefactions. Transverse Waves: The vertical distance from crest or trough of a wave to the rest positon of the medium. The amplitude of any transverse wave is also half the vertical distance from crest to trough.

Intensity

Amount of energy that flows through a certain a rea in a given amount of time.

Carrier waves transmit a signal in one of two ways which are?

Amplitude Modulation (AM): AM radio broadcasts information by varying the amplitude of th carrier wave. Frequency Modulation (FM): FM Radio waves caries the frequency of carrier.

Radar

Another use for radio waves is to find the position and movement of objects by a method called radar. Radar stands for RAdio Detecting And Ranging. With radar, radio waves are transmitted toward an object. By measuring the time required for the waves to bounce off the object and return to a receiving antenna, the location of the object can be found. Radar is used for tracking the movement of aircraft, watercraft, and spacecraft, as shown in Figure 8. Law enforcement officers also use radar to measure how fast a vehicle is moving.

Receiving radio waves

As electromagnetic waves pass by your radio's antenna, the electrons in the metal vibrate, as illustrated in Figure 21. These vibrating electrons produce a changing electric current that contains the information about the music and words. This current is used to make the speakers vibrate, creating the sound waves that you hear.

Television

Audio is sent by a FM Radio waves and video is sent by AM radio signals Cathode ray tubes- Produce images you see on Tv. Surface is covered by spots that glow red, green, or blue when struck by electron beams.

Particles as waves

Because electromagnetic waves could behave as particles, other scientists wondered whether particles, such as electrons, could behave as waves. If a beam of electrons was sprayed at two tiny slits, you might expect that the electrons would strike only the area behind the slits, like the spray paint at the left of Figure 6. But scientists found that the electrons formed an interference pattern typical of waves, as seen in the right of Figure 6. When waves pass through narrow slits, they interfere with each other. This experiment showed that electrons can behave like waves. It is now known that all particles can behave like waves. However, this does not mean that particles travel in wavy lines. Rather, this means that they display behavior, such as interference, that was once associated only with waves

Give two real world examples of refraction of light

Camera and Microscope

What kind of waves are sound waves

Compressionaly waves formed from vibrating objectsc ollding with air molecules.

Radio Transmissions

Each radio station uses an assigned frequency to avoid interfering with other radio broadcasts. Television stations and cell phone companies are also assigned specific frequencies. These frequency ranges are shown in Figure 18. The remaining radio frequencies are assigned for other purposes, such as navigation and radio astronomy. Changing the channel on your radio or television allows you to select a particular frequency carrying the information you want to listen to or watch. An electromagnetic wave with the specific frequency that a station is assigned is called a carrier wave. Modulation The station must do more than simply transmit a carrier wave. It must also send information about the sounds that you are to receive. The sounds produced at the radio station are converted into electric signals. This electric signal is called the signal wave and is used to modify the carrier wave. The process of adding the signal wave to the carrier wave is called modulation. There are two ways to modulate carrier waves: amplitude modulation (AM) and frequency modulation (FM). AM radio An AM radio station broadcasts information by varying the amplitude of the carrier wave, as shown at the left in Figure 19. AM carrier wave frequencies range from 540,000 to 1,600,000 Hz. FM radio In FM radio signals, the signal wave is used to vary the frequency of the carrier wave, as shown at the right in Figure 19. Because the strength of the FM waves is kept fixed, FM signals tend to be more clear than AM signals. FM carrier frequencies range from 88 million to 108 million Hz. These frequencies are much higher than AM frequencies.

Telephones

Electrical signal creates radio wave that is transmitted to and from a microwave

Electromagnetic Waves

Electromagnetic waves are made by vibrating electric charges. Electromagnetic waves are composed of changing electric fields and magnetic fields. Instead of transferring energy from particle to particle, electromagnetic waves travel by transferring energy between the electric and magnetic fields. Electromagnetic waves do not require matter to travel because electric fields and magnetic fields can exist where matter is not present.

A Range of Frequencies

Electromagnetic waves have a wide variety of frequencies. They might vibrate once each second or trillions of times each second. The entire range of electromagnetic wave frequencies is called the electromagnetic spectrum. A spectrum is a continuous sequence arranged by a particular property. Each region of the electromagnetic spectrum has a specific name, as shown in Figure 7. Each region interacts with matter differently. The human eye detects only a small portion of the electromagnetic spectrum called visible light. Various devices have been developed to detect other frequencies. For example, the antenna of your radio detects radio waves

Microwaves

Electromagnetic waves with wavelengths between 0.1 mm and 30 cm are called microwaves. Microwaves with wavelengths of about 1 cm to 20 cm are widely used for communication, such as for cellular telephones and satellite signals. However, you are probably most familiar with microwaves because of their use in microwave ovens. Microwave ovens In a microwave oven, microwaves interact with the water molecules in food, as shown in Figure 10. Each water molecule has a slight positive charge on one side and a slight negative charge on the other side, so it will align in an electric field. The vibrating electric field inside a microwave oven causes water molecules in food to rotate back and forth billions of times each second . This rotation causes a type of friction between water molecules that generates thermal energy. The thermal energy produced by the water molecules interactions causes your food to cook. Foods with plenty of water cook well in the microwave. Frozen water, however, cannot be warmed using microwaves because the water molecules are bound in a crystallized structure and cannot rotate. On many microwave ovens, there is a special defrost setting. This setting heats the partly melted water on the surface of the food. The inside of the food is then warmed by conduction until all the water is liquid again.

X-rays

Electromagnetic waves with wavelengths between about ten billionths of a meter and ten-trillionths of a meter are called X-rays. X-rays have shorter wavelengths than UV waves and their photons have larger energies. X-rays penetrate skin and soft tissue but not denser materials, such as teeth and bones. Doctors and dentists use low doses of X-rays to form images, like the one in Figure 16, of bones and teeth. X-rays are also used in airport screening devices to examine the contents of luggage.

Gamma Rays

Electromagnetic waves with wavelengths shorter than about 100-trillionths of a meter are called gamma rays. Gamma rays have high frequencies and have the highest-energy photons. They have enough energy to penetrate several centimeters of lead. Gamma rays are produced by processes that occur in the nuclei of atoms. Both X-rays and gamma rays are used in a technique called radiation therapy to kill diseased cells in the human body. A beam of X-rays or gamma rays can damage the biological molecules in living cells, causing both healthy and diseased cells to die. By carefully controlling the amount of X-ray or gamma ray radiation and focusing it on the diseased area, the damage to healthy cells can be reduced during treatment. Figure 17 shows a patient receiving radiation to treat cancer. The gamma rays are focused on the tumor and kill the cancer cells, while doing little damage to the surrounding healthy cells.

Radio Waves

Even though you cannot see them, radio waves are all around you. Radio waves are electromagnetic waves with wavelengths longer than 10 cm. Radio waves have long wavelengths and low frequencies, and their photons have low energies. Radio waves have many uses, including communications and medical imaging

Seismic waves

Forces within Earth's interior can cause regions of Earth's crust to move, bend, or even break. Movement in the crust, which occurs along faults, can result in a rapid release of energy. This energy travels away from the fault in the form of seismic (SIZE mihk) waves, as shown in Figure 6. Seismic waves can be longitudinal waves or transverse waves. Scientists have found out much about Earth's interior by studying these seismic waves. Seismic waves can travel through Earth, as well as along Earth's surface. When the energy from seismic waves is transferred to objects on Earth's surface, those objects move and shake.

The Global Positioning System

Getting lost while hiking is not uncommon; but if you are carrying a Global Positioning System receiver, it is much less likely to happen. The Global Positioning System (GPS) is a system of satellites, ground monitoring stations, and receivers that determine your exact location at or above Earth's surface. The 24 satellites necessary for 24-hour, around-the-world coverage became fully operational in 1995. Figure 26 illustrates how these satellites are arranged in orbit. Signals from four satellites are used to determine the location of an object using a GPS receiver. GPS satellites are owned and operated by the United States Department of Defense, but the microwave signals they send out can be used by anyone. Several other countries are working to develop similar systems. Airplanes, ships, cars, and cell phones can use GPS for navigation. Some pet collars also contain GPS receivers. If the pet runs away or is lost, the GPS receiver in the collar can be used to locate the animal.

Diffraction and wavelength

How much does a wave bend when it strikes an object or an opening? The amount of diffraction that occurs depends on how big the obstacle or opening is compared to the wavelength, as shown in Figure 20. When an obstacle is roughly the same size as or smaller than the wavelength of a wave, the wave bends around it. But when the obstacle is much larger than the wavelength, the waves do not diffract as much. If the obstacle is much larger than the wavelength, almost no diffraction occurs. Instead, the obstacle casts a shadow. Hearing around corners Suppose you are walking down the hallway, and you hear sounds coming from a classroom on the left before you reach the open classroom door. However, you cannot see into the room until you reach the doorway. Why can you hear the sound waves but not see the light waves while you are still in the hallway? The wavelengths of sound waves are similar in size to a door opening. Sound waves diffract around the door and spread out down the hallway. Light waves have a much shorter wavelength. They are hardly diffracted at all by the door. So, you cannot see into the room until you get to the door. Diffraction of radio waves Diffraction also affects your radio's reception. AM radio waves have longer wavelengths than FM radio waves do. Because of their longer wavelengths, AM radio waves diffract around obstacles, such as buildings and mountains. The FM waves with their short wavelengths do not diffract as much. As a result, AM radio reception is often better than FM reception around tall buildings and natural barriers, such as hills

Refraction

If a wave is traveling at an angle when it passes from one medium to another, it changes direction or bends, as it changes speed. It is the bending of a wave caused by a change in its speed as it travels from one medium to another. The greater the change speed, the more the wave bends. When light travels from air to water, they slow down and bend toward the normal. When light waves travel fom water to air, they sped up and bend away from the normal.

Wavelength is related to frequency

If you make transverse waves with a rope, you increase the frequency by moving the rope up and down faster. Moving the rope faster also makes the wavelength shorter. This relationship is always true. As frequency increases, wavelength decreases. If you double the frequency of a wave you halve the wavelength. If you double the wvaelength you halve the frequency. The frequency of a wave is always equal to the rate of vibration of the source that creates it. If you move the rope up, down and back up in 1s, the frequency you have is 1Hz. If you move the rope up, down, and back up five times in 1s, the resulting wave has a frequency of 5Hz.

Sound travels faster in?

In solids and liquid, molcules are close together than gas molecules. As medium temperature rises, molecules move faster conducting sound waves faster.

Magnetic resonance imaging (MRI)

In the early 1980s, medical researchers developed a technique called magnetic resonance imaging, which uses radio waves to help diagnose illness. The patient lies inside a large cylinder, like the one shown in Figure 9. The cylinder contains a powerful magnet, a radio wave emitter, and a radio wave detector. Protons in hydrogen atoms in bones and soft tissue behave like magnets and align with the strong magnetic field created by the machine's magnet. Some of the protons absorb energy from the radio waves and flip their alignments. The amount of energy a proton absorbs and then re-emits depends on the type of tissue it is part of. A radio receiver detects this released energy. This information is then used to create a map of the different tissues. A picture of the inside of the patient's body is produced painlessly

As the elasticity of a medium increases, the speed of sound ____

Increases

Loudness is the human perception of sound wave

Intensity

Telephones

Just a few decades ago, telephones had to be connected with wires. Today, cell phones are seen everywhere. When you speak into a telephone, a microphone converts the sound waves into an electric signal. In a cell phone, this signal is transmitted to and from microwave towers using microwaves or radio waves.The towers, like the ones in Figure 23, are several kilometers apart and each covers an area called a cell. If you move from one cell to another, an automated control station transfers the ignal to the new cell and its tower. Transceivers A cell phone is a transceiver. A transceiver transmits one radio signal and receives another radio signal.Using two signals with different frequencies allows you to talk and listen at the same time without interference. Cordless telephones are also transceivers. However, you must remain close to the base unit when using a cordless phone. Another drawback is that if someone nearby is using a cordless telephone at the same frequency, you could hear that conversation on your phone. For this reason, many cordless phones have a channel button that allows you to switch to another frequency. Pagers Some hospitals ban cell phone use because there are concerns that transceivers might interfere with medical equipment. So, many doctors carry small, portable radio receivers called pagers. To contact the doctor, a caller leaves a callback number or a text message at a central terminal. The message is changed into an electronic signal and transmitted by radio waves along with the identification number of the desired pager. The pager receives all messages transmitted at its assigned frequency, but it only responds to messages with its identification number. Restaurants also use pagers, like the one in Figure 24, to notify customers that their tables are ready

Wave Speed

Light waves travel faster than sound waves which is why you see the impact of a baseball before you hear the sound. The speed of a wave depends on the medium. Sound waves travel faster in liquid, and slower in solids. Light waves travel more slowly in liquids and solids than they do in gases or in a vacuum. Sound waves travel faster if temperature is increases. Equation: Speed (in m/s)= Frequency (in Hz) x wavelength (in m) v= fy V= wave speed f= frequency

Frequency and wavelength

Like all waves, electromagnetic waves can be described by their wavelengths and frequencies. The wavelength of an electromagnetic wave is the distance from one crest to another, as shown in Figure 3. The frequency is the number of wavelengths that pass a point in one second. The units for frequency are hertz. The frequency of an electromagnetic wave equals the frequency of the vibrating charge that produces the wave. This frequency is the number of vibrations of the charge in one second. Electromagnetic waves follow the wave speed equation, v = f λ. As the frequency (f) increases, the wavelength (λ) becomes smaller.

The two types of mechanical waves

Longitudinal and Transverse Waves

Parts of a Longitudinal Wave

Longitudinal waves have no crests or troughs. When it passes through a medium it creates regions where the medium becomes crowed together and more dense, these are compressions. A compression is the more dense region of a longitudinal wave. The less dense region of a longitudinal wave is called a rarefaction.

Longitudinal Wave

Matter in the medium moves back and forth along the same direction that the wave travels. Imagin e acoled spring toy. Squeeze several cols together at one end of the spring. Then let go of the coils, still holding onto cols at both ends of the spring. A wave will travel along the spring. It looks as if the whole spring is moving toward one end.

How does elasticity affect sound speed? Explain

More elasticity makes the particles get back in regular positions faster so they can collide more often.

Infrared Waves

Most of the warm air in a fireplace moves up the chimney, yet you feel the warmth of the blazing fire when you stand in front of a fireplace. Why do you feel the warmth? The warmth you feel is thermal energy transmitted to you by infrared waves. Infrared waves are electromagnetic waves with wavelengths between about one-thousandth of a meter and about 700-billionths of a meter. Using infrared waves Every object emits infrared waves. Hotter objects emit more infrared waves than cooler objects. Infrared detectors can form images of objects from the infrared waves they emit. These images, like the one in Figure 11, can help determine how energy-efficient a structure is. Other devices that use infrared waves include television remote controls and CD-ROM drives.

Frequency

Number of wavelengths that make pass a fixed point each second. Also the number of times that a point on a wave moves up and down or back and forth each second. You can find the frequency on a longitudinal wave by counting the number of compressions that pass a point each second. Frequency is expressed in hertz(Hz). A frequency of 1Hz means that one wavelength passes by in 1s. In SI units, 1Hz is the same as 1/s. The period of a wave is the amount of tme it takes one wavelength to pass a point. As the frequency of a wave increases, the period decreases. In SI units, period has units of seconds.

Reflection

Occurs when a wave strikes an object and bounces off of it. All types of waves can be reflected. Reflection in a mirror happens first when light strikes her face and bounces off her face. Then the light reflected off her face strikes the mirror and is reflected into her eyes. Echoes: result of reflecting sound waves. Dolphins use clicking noises to learn about their environment. The law of Reflection: The beam striking the mirror is called the incident beam and the beam that bounces off the mirror is called the reflected beam. The line drawn perpendicular to the surface of the mirror is called the normal. The angle formed by the incident beam and the normal is the angle of incidence, labeled i. The angle formed by the reflected beam and the normal is the angle of reflection, labeled r. Angle of Incidence is always equal to angle of reflection. All reflected waves obey this law.

Transverse Wave

Particles in the medium move back and forth at right angles to the direction that the wavetravels.

List the order of the Electromagnetic Spectrum (R.I.V.U.X.G)

Radio Waves, Infrared waves, Visible light, Ultraviolet waves, X-rays and Gamma rays

Electromagnetic Spectrum includes:

Radio Waves: Low frequency waves with a wavelength of about 1-10 cm. (Radio Stations, Microwaves, radar) Infrared Wave: Have slightly higher frequency than radio waves. Visible Light: Range of electromagnetic waves you can detect with your eyes. (ROYGBIV)- Different colors have different wave lengths Ultraviolet waves- frequencies slightly higher than visible light (Sunburns, vitamin D production, fluorescent materials absorb it, kills materials) X-rays and Gamma rays- Ultra high frequencies that can travel through matter , damage cells (burn images, radiation therapy, )

Radio transmission

Radio converts electromagnetic waves into sound waves

Electric and magnetic fields

Recall that electric charges are surrounded by electric fields and that magnets are surrounded by magnetic fields. These fields exert a force even when the charge or magnet is not in contact with an object. Fields exist around an electric charge or a magnet even in a vacuum. A vacuum is a volume of space that contains little or no matter. You might also recall that a moving electric charge, such as the current in the wire shown in Figure 2, is surrounded by a magnetic field. Similarly, a moving magnet is surrounded by an electric field. A changing electric field creates a magnetic field, and a changing magnetic field creates an electric field.

Wavelength (Transverse and Longitudinal Wave)

The distance between one point on a wave and the nearest point just like it. For transverse waves the wavelength is from trough to trough or crest to crest. The two distances are equal on a transverse wave. On a longitudinal wave it is the distance from the middle of one compression to the middle of the next compression. It is also the distance from the middle of one rarefraction to the middle of the next rarefaction. The two are equal.

Communications Satellites

Since satellites were first developed, thousands have been launched into Earth's orbit. Many of these, like the one in Figure 25, are used for communication. The sender broadcasts a microwave signal to the satellite. The satellite receives the signal, amplifies it, and transmits it to a particular region on Earth. Like cell phones, satellites are transceivers. To avoid interference, the satellite receives signals at one frequency and broadcasts signals at a different frequency. Satellite telephone systems Some mobile telephones can be used when sailing across the ocean, even though there are no nearby cell phone towers. The telephone transmits the signal directly to a satellite. The satellite relays the signal to a ground station, and the call is passed on to the telephone network. Satellite links work well for one-way transmissions, but two-way communications can have a delay caused by the large distance the signals travel to and from the satellite. Television satellites The satellite-reception dishes that you sometimes see in yards or attached to houses are receivers for television satellite signals. Satellite television is used as an alternative to ground-based transmission. Communications satellites use microwaves rather than the radio waves used for normal television broadcasts. Microwaves have shorter wavelengths and travel more easily through the atmosphere. The ground receivers are dish-shaped to help focus the microwaves onto an antenna.

Audio transmission

Some radio waves carry an audio signal from a radio station to a radio. However, even though these radio waves carry information that a radio uses to create sound, you cannot hear radio waves. You hear sound when your radio changes the radio wave into a sound wave.

Sound waves

Sound waves are longitudinal waves. When a noise is made, such as when a locker door slams shut, nearby molecules in the air are pushed together by the vibrations caused by the slamming door. The molecules in the air are squeezed together similar to the coils in the coiled spring toy in Figure 5. These compressions travel through the air to make a sound wave. The sizes of a sound wave's compressions, as well as the distances between those compressions, determines the nature of that sound. Sound waves in liquids and solids Sound waves can also travel through liquids and solids, such as water and wood. Particles in these mediums are pushed together and move apart as the sound waves travel through them

Human hearing involves four stages:

Stage 1: Ear gathers compressional waves which vibrate a tough membrane called: eardrum. Stage 2: The middle ear has three bones called: hammer, anvil, and stirrup which amplify sound waves. Stage 3: The inner ear contains the cochlea which vibrates sending auditory nerves. Stage 4: Brain decodes and inerprets nerve impulses.

Mechanical Wave

Such as sound waves are waves that can only travel through matter. Can be either transverse or longitudinal waves.

Global Positioning System (GPS)

System of satellites, ground stations and receivers that receive high frequency microwaves signals, amplify it and return it

Speed of sound depends on?

Temperature and state of medium

Waves and Particles

The difference between a wave and a particle might seem obvious—a wave is a disturbance that carries energy, and a particle is a piece of matter. However, in reality, the difference is not so clear. Waves as particles In 1887, Heinrich Hertz found that he could create a spark by shining light on a metal. (Today, we know that this spark means that electrons were ejected from the metal.) Hertz found that whether sparks occurred depended on the frequency of the light and not the amplitude. Because the energy carried by a sound wave or water wave depends on its amplitude and not its frequency, this result was mysterious. In 1905, Albert Einstein provided an explanation. An electromagnetic wave can behave as a particle called a photon. A photon is a massless bundle of energy that behaves like a particle. The photon's energy depends on the frequency of the wave. The photon's energy increases as the wave's frequency increases.

What does a sound's frequency most influence?

pitch

Properties of Electromagnetic Waves

The vibrating electric and magnetic fields of an electromagnetic wave are perpendicular to each other. That is, they are at right angles (90°) to each other. They travel outward from the moving charge, as shown in Figure 3. Because the electric and magnetic fields vibrate at right angles to the direction the wave travels, an electromagnetic wave is a transverse wave. Speed In a vacuum, all electromagnetic waves travel at 300,000 km/s. Because light is a type of electromagnetic wave, the speed of electromagnetic waves in a vacuum is usually called the "speed of light." The speed of light is nature's speed limit—nothing travels faster than the speed of light. The speed of an electromagnetic wave in matter depends on the material through which the wave travels. However, it is always slower than the speed of light in a vacuum. In matter, electromagnetic waves are usually the slowest in solids and faster in gases. Table 1 in Figure 4 lists the speed of electromagnetic waves in a vacuum and several common materials. Figure 4 illustrates that light travels slower and refracts when it enters glass.

What are electromagnetic wave

They are made by vibrating electric charges and travel through space

Ultraviolet Waves

Ultraviolet waves are electromagnetic waves with wavelengths from about 400-billionths to 10-billionths of a meter. Ultraviolet waves (UV waves) can enter cells, making ultraviolet waves both useful and harmful. Useful UVs You probably know that UV waves cause sunburn. But some exposure to ultraviolet waves is healthy. Ultraviolet waves striking the skin enable your body to make vitamin D, which is needed for healthy bones and teeth. Ultraviolet waves are also used to disinfect food, water, and medical supplies, as shown in Figure 13. When ultraviolet light enters a cell, it damages protein and DNA. For some single celled organisms, such as bacteria, this damage can mean death. Ultraviolet waves make some materials fluoresce (floo RES). Materials that fluoresce absorb ultraviolet waves and reemit the energy as visible light. Police detectives sometimes use fluorescent powder to reveal fingerprints. Harmful UVs When you spend time in the Sun, you might wear sunscreen to prevent sunburn. Most of the UV waves that reach Earth's surface are longer-wavelength UVA rays. The shorter-wavelength UVB rays are the primary cause of sunburn and skin cancers, but UVA rays contribute to skin cancers and skin damage, such as wrinkling. The ozone layer About 20 to 50 km above Earth's surface is a region called the ozone layer. Ozone is a molecule composed of three oxygen atoms. The ozone layer is vital to life on Earth because it absorbs most of the Sun's harmful ultraviolet waves and prevents them from reaching Earth's surface, as shown in Figure 14.

The Digital Revolution

Until the early 21st century, information was sent to TV sets in the same way it was sent to radios. The audio information was sent using FM, and the visual information was sent using AM. The information signals were analog signals. Analog signals are electric signals whose values change smoothly over time. In 2009, full-power television stations in theUnited States began broadcasting only digital signals. A digital signal is an electric signal where there are only two possible values: ON and OFF. This is similar to a light switch where the light can be on or off, but it cannot be half-on or half-off. There are many ways to modulate radio waves using this on-and-off information. The simplest methods, however, resemble traditional AM and FM and are called Amplitude-Shift Keying (ASK) and Frequency-Shift Keying (FSK). These types of digital modulation are shown in Figure 22. More complex ways of digital modulation allow more information to be carried by a single wave. In the United States, television stations use multiple amplitude modulations to encode data on the carrier wave.

Visible Light

Visible light is the range of electromagnetic waves that you detect with your eyes. Visible light differs from radio waves, microwaves, and infrared waves only by its frequency and wavelength. Visible light has wavelengths around 700-billionths to 400-billionths of a meter. Color is the brain's interpretation of the wavelengths of the light absorbed by substances in the eye. These colors range from short-wavelength violet to long wavelength red, as illustrated in Figure 12. If all colors of light are present in the same place, you see the light as white.

Waves in Matter

Waves are produced by something that vibrates, and they carry energy from one place to another. Look at the water wave and the sound wave in Figure 1. Both waves are moving through matter. The water wave is moving through water, and the sound wave is moving through air. These waves travel because energy is transferred from particle to particle. Without matter to transfer the energy, these waves cannot move. However, there is another type of wave that does not require matter to transfer energy.

Both refraction and diffraction cause

Waves to bend, however, refraction occurs when waves pass through an object while diffraction occurs when waves pass around an object.

Making electromagnetic waves

When an electric charge vibrates, the electric field around it changes. Because the electric charge is in motion, it also has a magnetic field around it. This magnetic field also changes as the charge vibrates. As a result, the vibrating electric charge is surrounded by a changing electric field and a changing magnetic field. How do the vibrating electric field and magnetic field around the charge become a wave that travels through space? The changing electric field around the charge creates a changing magnetic field. This changing magnetic field then creates a changing electric field. This process continues, with the magnetic field and electric field continually creating each other

Water waves

When the wind blows across the surface of the ocean, water waves form. Water waves are often thought of as transverse waves, but this is not entirely correct. The water in water waves does move up and down as the waves go by. But the water also moves short distances back and forth along the direction that the wave is traveling. This movement happens because the low part of the wave can be formed only by pushing water forward or backward toward the high part of the wave, as shown on the left in Figure 4. This is much like a child pushing sand into a pile. Sand must be pushed in from the sides to make the pile. As the wave passes, the water that was pushed aside moves back to its initial position, as shown on the right in

Interference

When two or more waves overlap to form a new wave. Suppose two waves travel toward each other on a long rope as in the top panel of Figure 21. What happens when the two waves meet? The two waves pass through each other, and each one continues to travel in its original direction, as shown in the middle and bottom panels of Figure 21. However, when the waves meet in the middle panel of Figure 21, they form a new wave that looks different from either of the original waves. When two waves arrive at the same place at the same time, they combine to form a new wave. Interference is the process of two or more waves overlapping and combining to form a new wave. This new wave exists only while the two original waves continue to overlap. Two waves can combine through either constructive interference or destructive interference. Constructive interference In constructive interference, as shown in the top panel of Figure 22, the waves add together. This happens when the crests of two or more transverse waves arrive at the same place at the same time and overlap. The amplitude of the new wave that forms is equal to the sum of the amplitudes of the original waves. Constructive interference also occurs when the compressions of different longitudinal waves overlap. If the waves are sound waves, for example, constructive interference produces a louder sound. Waves undergoing constructive interference are said to be in phase. Destructive interference In destructive interference, the waves subtract from each other as they overlap. This happens when the crests of one transverse wave meet the troughs of another transverse wave, as shown in the bottom panel of Figure 22. The amplitude of the new wave is the difference between the amplitudes of the waves that overlapped. With longitudinal waves, destructive interference occurs when the compression of one wave overlaps with the rarefaction of another wave. One way to think of this is that the compressions of one wave "fill in" the rarefactions of another wave. Th compressions and rarefactions combine and form a wave with reduced amplitude. When destructive interference happens with sound waves, it causes a decrease in loudness. Waves undergoing destructive interference are said to be out of phase.

Diffraction

When waves strike an object, several things can happen. The waves can be reflected. If the object is transparent, light waves can be refracted as they pass through it. Often, some waves are reflected and some waves are refracted. If you look into a glass window, sometimes you can see your reflection in the window, as well as objects behind it. Light is passing through the window and is also being reflected at its surface. Waves can also behave another way when they strike an object. The waves can bend around the object. Figure 18 shows ocean waves changing direction and bending after they strike an island. Diffraction is the bending of a wave around an object. Diffraction and refraction both cause waves to bend. The difference is that refraction occurs when waves pass through an object, while diffraction occurs when waves pass around an object. All waves, including water waves, sound waves, and light waves, can be diffracted. Less diffraction occurs if the wavelength is smaller than the obstacle. More diffraction occurs if the wavelength is the same size as the obstacle.

Standing waves

When you make transverse waves on a rope, you might attach one end to a fixed point, such as a doorknob, and shake the other end. The waves that you produce then reflect back from the doorknob. What happens when the incident and reflected waves meet? As the two waves travel in opposite directions along the rope, they continually pass through each other. Interference takes place as the waves from each end overlap along the rope. At any point where a crest meets a crest, a new wave with a larger amplitude forms. But at points where crests meet troughs, the waves cancel each other and no motion occurs. The interference of the two identical waves makes the rope vibrate in a special way, as shown in Figure 23. The waves create a pattern of crests and troughs that do not seem to be moving. Because the wave pattern stays in one place, it is called a standing wave. A standing wave is a special type of wave pattern that forms when waves equal in wavelength and amplitude but traveling in opposite directions continuously interfere with each other. Standing waves have nodes, which are locations where the interfering waves always cancel. The nodes always stay in the same place on the rope. Meanwhile, the wave pattern vibrates between the nodes Standing waves in music When the string of a violin is played with a bow, it vibrates and creates standing waves. The standing waves in the string help produce a rich, musical tone. Other instruments also rely on standing waves to produce music. Some instruments, such as flutes, create standing waves in a column of air. In other instruments, such as drums, a tightly stretched piece of material vibrates in a special way to create standing waves. As the material in a drum vibrates, nodes are created on the surface of the drum.

Resonance

When you were younger, you might have played on a swing like the one in Figure 24. You probably noticed that you could make the swing go higher by pumping your legs and arms. It was not necessary to pump hard, but timing was important. If you pumped in time to the swing's rhythm, you could go quite high. You can accomplish similar effects with sounds. Suppose you have a tuning fork that has a single natural frequency of 440 Hz, which means that the tuning fork naturally vibrates at 440 Hz when struck. Now think of a sound wave with a frequency of 440 Hz strikes the tuning fork. Because the sound wave has the same frequency as the natural frequency of the tuning fork, the tuning fork will begin to vibrate. Resonance is the process by which an object is made to vibrate by absorbing energy at its natural frequencies. Sometimes resonance can cause an object to absorb a large amount of energy. An object vibrates more and more strongly as it absorbs energy at its natural frequencies. If the object absorbs enough energy, it might break.

Which sound wave property is most related to loudness?

amplitude

Loudness

human perception of sound intensity which is measured in decibles (db)

electromagnetic waves with wavelengths between 0.1 mm and 30 cm electromagnetic waves with wavelengths from about 400-billionths to 10-billionths of a meter electromagnetic waves between about 10-billionths of a meter and 1-trillionths of a meter electromagnetic waves shorter than about 100-trillionths of a meter electromagnetic waves with wavelengths longer than 10 cm electromagnetic waves with wavelengths between about 1-thousanth meter and about 700-billionths of a meter

microwave, ultraviolet waves, x-rays, gamma rays, radio rays, infrared rays

Section Summary

◗ Incandescent and fluorescent lightbulbs are often used in homes, schools, and offices. ◗ When electrons collide with neon gas, red light is emitted. ◗ A tungsten-halogen bulb is brighter and hotter than an ordinary incandescent bulb. ◗ Lasers emit narrow beams of coherent light.

Section Summary

◗ Refracting telescopes use two convex lenses to gather and focus light. ◗ Reflecting telescopes use a concave mirror, a plane mirror, and a convex lens to collect, reflect, and focus light. ◗ Placing a telescope in orbit avoids the distorting effects of Earth's atmosphere. ◗ A microscope uses two convex lenses with short focal lengths to magnify small, close objects. ◗ A camera lens focuses light onto an image sensor.

Section Summary

◗ The color of an object depends on the wavelengths of light it reflects. ◗ Rod and cone cells are light-sensitive cells found in the human eye. ◗ The color of a filter is the color of the light that the filter transmits. ◗ All light colors can be created by mixing the primary light colors—red, green, and blue. ◗ All pigment colors can be formed by mixing the primary pigment colors—magenta, cyan, and yellow.

Section Summary

◗ The magnetic fields in linearly polarized light vibrate in only one direction. ◗ Polarizing filters transmit light polarized in one direction. ◗ Lasers are used to produce holograms. ◗ The complete reflection of light at the boundary between two materials is called total internal reflection.