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6. How are visible light and a radio wave different? How are they
FOR FURTHER ANALYSIS
the same?
1. Clarify the distinction between light reflection and light
refraction by describing clear, obvious examples of each. INVITATION TO INQUIRY
2. Describe how you would use questions alone to help someone
understand that the shimmering she sees above a hot pavement Best Sunglasses?
is not heat.
Obtain several different types of sunglasses. Design experiments to de-
3. Use a dialogue as you “think aloud,” considering the evidence termine which combination of features will be found in the best pair of
that visible light is a wave, a particle, or both.
sunglasses. First, design an experiment to determine which reduces re-
4. Compare and contrast the path of light through a convex lens flected glare the most. Find out how sunglasses are able to block ultra-
and a concave lens. Give several uses for each lens, and describe violet radiation. According to your experiments and research, describe
how the shape of the lens results in that particular use.
the “best” pair of sunglasses.
5. Analyze how the equation E = hf could mean that visible light is
a particle and a wave at the same time.

PARALLEL EXERCISES

The exercises in groups A and B cover the same concepts. Solutions to group A exercises are located in appendix E.
Group A Group B
1. What is the speed of light while traveling through (a) water and 1. What is the speed of light while traveling through (a) a vacuum,
(b) ice? (b) air at 30°C, and (c) air at 0°C?
2. How many minutes are required for sunlight to reach Earth if the 2. How much time is required for reflected sunlight to travel from
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Sun is 1.50 × 10 km from Earth? the Moon to Earth if the distance between Earth and the Moon is
5
3.85 × 10 km?
3. How many hours are required before a radio signal from a space 3. How many minutes are required for a radio signal to travel
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probe near Pluto reaches Earth, 6.00 × 10 km away? from Earth to a space station on Mars if the planet Mars is
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7.83 × 10 km from Earth?
4. A light ray is reflected from a mirror with an angle 10° to the 4. An incident light ray strikes a mirror with an angle of 30° to the
normal. What was the angle of incidence? surface of the mirror. What is the angle of the reflected ray?
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5. Light travels through a transparent substance at 2.20 × 10 m/s. 5. The speed of light through a transparent substance is
8
What is the substance? 2.00 × 10 m/s. What is the substance?
6. The wavelength of a monochromatic light source is measured to 6. A monochromatic light source used in a diffraction experiment
–7
–7
be 6.00 × 10 m in a diffraction experiment. (a) What is the has a wavelength of 4.60 × 10 m. What is the energy of a
frequency? (b) What is the energy of a photon of this light? photon of this light?
2
7. At a particular location and time, sunlight is measured on a 1 m 7. In black-and-white photography, a photon energy of about
–19
solar collector with a power of 1,000.0 W. If the peak intensity of 4.00 × 10 J is needed to bring about the changes in the silver
–7
this sunlight has a wavelength of 5.60 × 10 m, how many compounds used in the film. Explain why a red light used in a
photons are arriving each second? darkroom does not affect the film during developing.
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8. A light wave has a frequency of 4.90 × 10 cycles per second. 8. The wavelength of light from a monochromatic source is
–7
(a) What is the wavelength? (b) What color would you observe measured to be 6.80 × 10 m. (a) What is the frequency of this
(see Table 7.2)? light? (b) What color would you observe?
9. What is the energy of a gamma photon of frequency 5.00 × 9. How much greater is the energy of a photon of ultraviolet
–7
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10 Hz? radiation (λ = 3.00 × 10 m) than the energy of an average
–7
photon of sunlight (λ = 5.60 × 10 m)?
10. What is the energy of a microwave photon of wavelength 1.00 mm? 10. At what rate must electrons in a wire vibrate to emit microwaves
with a wavelength of 1.00 mm?
11. What is the speed of light traveling through glass? 11. What is the speed of light in ice?
–7
12. What is the frequency of light with a wavelength of 5.00 × 10 m? 12. What is the frequency of a monochromatic light used in a
–7
diffraction experiment that has a wavelength of 4.60 × 10 m?
13. What is the energy of a photon of orange light with a frequency 13. What is the energy of a photon of red light with a frequency of
14
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of 5.00 × 10 Hz? 4.3 × 10 Hz?
14. What is the energy of a photon of blue light with a frequency of 14. What is the energy of a photon of ultraviolet radiation with a
–7
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6.50 × 10 Hz? wavelength of 3.00 × 10 m?
2
15. At a particular location and time, sunlight is measured on a 1 m 2 15. At a particular location and time, sunlight is measured on a 1 m
solar collector with an intensity of 1,000.0 watts. If the peak solar collector with an intensity of 500.0 watts. If the peak intensity
–7
–7
intensity of this sunlight has a wavelength of 5.60 × 10 m, how of this sunlight has a wavelength of 5.60 × 10 m, how many
many photons are arriving each second? photons are arriving each second?
202 CHAPTER 7 Light 7-26