Chapter 16 Sound and Light

Science Spectrum Answer Key continued

Chapter 16 Sound and Light

SECTION 1 SOUND 1. Student should label an area with close-

together air particles "Compression" and an area with far-apart air particles "Rarefaction."

2. longitudinal 3. cold air 4. Rubber absorbs or reduces vibrations, so

sound waves do not travel through it well.

5. the energy in the waves 6. When the drum is hit gently, less energy is

transmitted to it. Therefore, it vibrates less, and the amplitude of the resulting sound waves is smaller. The smaller amplitude produces a reduced intensity, or loudness.

7. 10 times 8. about four times 9. Trombones generally play lower-pitched,

and therefore lower-frequency, sounds than trumpets.

10. the dolphin 11. standing waves 12. the frequency of the main standing wave on

a vibrating string

13. the top 14. the frequencies at which an object is most

likely to vibrate

15. More air molecules are in contact with the guitar body.

16. through the outer ear 17. outer ear, middle ear, inner ear 18. a long, flexible membrane in the cochlea 19. They do not harm living cells. 20. no 21. The images are produced using ultrasound

waves.

22. a tool that uses reflected sound waves to measure distances

23. Student should circle the highest point on the ocean floor.

Review 1. Both infrasound and ultrasound are outside the range of normal human hearing. Infrasound has lower frequencies than humans can hear. Ultrasound has higher frequencies than humans can hear. 2. amplitude and distance from source 3. The first sound has a lower frequency and smaller amplitude than the second sound. 4. left to right: outer ear; eardrum; middle ear; cochlea 5. Both involve using sound waves to measure or make images. Sonograms are images of the human body. Sonar is used to produce images of the ocean floor or other objects.

SECTION 2 THE NATURE OF LIGHT 1. They diffract. 2. transverse waves 3. Any three of the following: reflection,

refraction, diffraction, interference 4. the bright red light 5. Possible answer: particles, photons 6. The bright red beam contains more photons

because it is brighter. Brighter lights contain more photons. 7. top row: wave model second row: particle model third row: wave model bottom row: particle model 8. photons 9. ultraviolet 10. air 11. The light spreads out as it travels. 12. Student should circle the largest area. 13. gamma rays 14. radio waves 15. a system that uses radio waves to locate objects 16. centimeters 17. a phone signal 18. temperature changes and cloud movements in the atmosphere 19. more

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Answer Key

Science Spectrum Answer Key continued

Review

1. Possible answers: police use radar to track the speed of vehicles; air-traffic control uses radar to track location and elevation of aircraft.

2. Neither model can completely explain all the observations about the behavior of light.

3. Observations that support the wave model include the fact that light shows reflection, refraction, diffraction, and interference. Observations that support the particle model include the fact that light can travel through a vacuum and that light can cause electrons to fly off pieces of metal.

4. The energy of photons of light is proportional to the frequency of the electromagnetic waves. Therefore, photons associated with visible light have more energy than photons associated with radio waves, because visible light has higher frequencies than radio waves.

5. UV light has high enough energy that it can pass through clouds. It can give you a sunburn. Sunscreen protects skin by absorbing or blocking ultraviolet light before it reaches your skin.

6. gamma rays,Xrays, ultraviolet rays, visible light, infrared light, microwaves, radio waves

SECTION 3 REFLECTION AND COLOR 1. an imaginary line that shows the direction in

which light travels

2. dull

3. The angle of incidence of a light ray is equal to the angle of reflection.

4. Student should draw an incoming ray that makes a smaller angle with the normal, and a reflected ray that makes the same angle with the normal, but is on the other side of the normal.

5. a virtual image

6. His brain interprets the reflected light waves as if they traveled in a straight line from behind the mirror.

7. They distort reflected images.

8. Light rays pass through a real image, but they do not pass through a virtual image.

9. the relative positions of the object and the mirror

10. the wavelengths of light it reflects

11. white 12. It absorbs all colors of visible light.

Review 1. to make it easier to understand and predict how light waves will behave during reflection and refraction

2. Answers will vary. Students should give examples of objects that are dull or matte in appearance. Objects that produce diffuse reflection look dull.

3. Student should label the vertical line "Normal," the angle between the downward-pointing line and the normal "Angle of incidence," and the angle between the upward-pointing ray and the normal "Angle of reflection."

4. Possible answers: 25?, or the same as the angle of incidence

5. A blue object reflects blue light. If you shine red light on it, there is no blue light for it to reflect, so it appears black.

SECTION 4 REFRACTION, LENSES, AND PRISMS 1. Its speed changes. 2. It decreases. 3. air 4. Light reflecting from below the water

refracts as it moves from the water to the air, producing a virtual image that your eye detects.

5. Student should circle the point at which all of the light rays converge.

6. virtual 7. Muscles around the lens change its shape to

change the amount that light is refracted.

8. violet 9. violet 10. the separation of light into different colors

because of differences in wave speed

11. dispersion and reflection

Review 1. Dispersion occurs because different wavelengths of light refract by different amounts when they pass through a prism.

2. In order of flow chart: cornea; lens; lens; retina; rods; cones; optic nerve

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Answer Key

Science Spectrum Answer Key continued

3. Possible answers: magnifying glass, human eye, microscope

4. Rainbows form because of a combination of dispersion and reflection. Dispersion happens because different wavelengths of light travel at different speeds in a medium. If all wavelengths of light traveled at the same speed in a given medium, no dispersion would occur, and rainbows would not form.

5. converging 6. green light

Chapter 17 Electricity

SECTION 1 ELECTRIC CHARGE AND FORCE 1. The particle has a positive charge. 2. electrons 3. They have opposite electric charges. 4. negative 5. 1.6 1019 C 6. Electrons are located in the outer parts of

an atom.

7. The toaster would not work if the cord were made entirely of plastic. Plastic is an insulator, so electricity does not flow through it easily.

8. It contains the same number of protons as electrons.

9. It has a negative charge, so it must have more electrons than protons.

10. friction 11. Electrons cannot move easily through an

insulator.

12. positive 13. a force a charged object experiences due to

interactions with other charged objects

14. amount of charge on each object and distance between the objects

15. away from each other 16. a force that can affect objects that are not

touching

17. because a positively charged object will repel another positively charged object

18. Electric field lines show how a positively charged particle would move. A positively charged particle would be repelled by the positively charged particles in the left image.

Review 1. In electrical conductors, electrons can move freely throughout the substance. Therefore, electrical conductors can transfer electric charge easily. In electrical insulators, electrons cannot move freely. Therefore, electrical insulators do not transfer electric charge easily.

2. There is more friction between your feet and a carpeted floor than between your feet and a smooth floor. The greater friction causes more electrons to move between the floor and your body.

3. More electrons will move into student A's body than into student B's body. Therefore, the difference in electric charge between student A and the doorknob will be greater. Student A is more likely to receive an electric shock.

4. The greater the charges, the greater the electric force.

5. toward the object

SECTION 2 CURRENT 1. energy that charged objects have that

depends on their position in an electric field

2. It decreases. 3. It would decrease. 4. voltage 5. 12 V 6. from areas of high potential to areas of low

potential

7. electrons 8. from right to left 9. the slowing of the movement of charged

particles through a substance

10. resistance 11. They travel through the wires in the bulb. 12. by dividing voltage by current 13. VIR;

V(0.50 A) ? (12 7); V6 V 14. Electrons can move through them easily. 15. Metal is a better electrical conductor than

plastic, so the metal fork probably has lower resistance than the plastic fork.

16. to allow electricity to flow through the device 17. a material that has no resistance below a

certain temperature

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Answer Key

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