Sections
Chapter Review

# Chapter Review

### Concept Items

#### 21.1Planck and Quantum Nature of Light

1.

What aspect of the blackbody spectrum forced Planck to propose quantization of energy levels in atoms and molecules?

1. Radiation occurs at a particular frequency that does not change with the energy supplied.
2. Certain radiation occurs at a particular frequency that changes with the energy supplied.
3. Maximum radiation would occur at a particular frequency that does not change with the energy supplied.
4. Maximum radiation would occur at a particular frequency that changes with the energy supplied.
2.

Two lasers shine red light at 650 nm. One laser is twice as bright as the other. Explain this difference using photons and photon energy.

1. The brighter laser emits twice the number of photons and more energy per photon.
2. The brighter laser emits twice the number of photons and less energy per photon.
3. Both lasers emit equal numbers of photons and equivalent amounts of energy per photon.
4. The brighter laser emits twice the number of photons but both lasers emit equivalent amounts of energy per photon.
3.

Consider four stars in the night sky: red, yellow, orange, and blue. The photons of which star will carry the greatest amount of energy?

1. blue
2. orange
3. red
4. yellow
4.
A lightbulb is wired to a variable resistor. What will happen to the color spectrum emitted by the bulb as the resistance of the circuit is increased?
1. The bulb will emit greener light.
2. The bulb will emit bluer light.
3. The bulb will emit more ultraviolet light.
4. The bulb will emit redder light.

#### 21.2Einstein and the Photoelectric Effect

5.
Light is projected onto a semi-conductive surface. However, no electrons are ejected. What will happen when the light intensity is increased?
1. An increase in light intensity decreases the number of photons. However, no electrons are ejected.
2. Increase in light intensity increases the number of photons, so electrons with higher kinetic energy are ejected.
3. An increase in light intensity increases the number of photons, so electrons will be ejected.
4. An increase in light intensity increases the number of photons. However, no electrons are ejected.
6.

True or false—The concept of a work function (or binding energy) is permissible under the classical wave model.

1. false
2. true
7.
Can a single microwave photon cause cell damage?
1. No, there is not enough energy associated with a single microwave photon to result in cell damage.
2. No, there is zero energy associated with a single microwave photon, so it does not result in cell damage.
3. Yes, a single microwave photon causes cell damage because it does not have high energy.
4. Yes, a single microwave photon causes cell damage because it has enough energy.

#### 21.3The Dual Nature of Light

8.
Why don’t we feel the momentum of sunlight when we are on the beach?
1. The momentum of a singular photon is incredibly small.
2. The momentum is not felt because very few photons strike us at any time, and not all have momentum.
3. The momentum of a singular photon is large, but very few photons strike us at any time.
4. A large number of photons strike us at any time, and so their combined momentum is incredibly large.
9.
If a beam of helium atoms is projected through two slits and onto a screen, will an interference pattern emerge?
1. No, an interference pattern will not emerge because helium atoms will strike a variety of locations on the screen.
2. No, an interference pattern will not emerge because helium atoms will strike at certain locations on the screen.
3. Yes, an interference pattern will emerge because helium atoms will strike a variety of locations on the screen.
4. Yes, an interference pattern will emerge because helium atoms will strike at certain locations on the screen.

### Critical Thinking Items

#### 21.1Planck and Quantum Nature of Light

10.
Explain why the frequency of a blackbody does not double when the temperature is doubled.
1. Frequency is inversely proportional to temperature.
2. Frequency is directly proportional to temperature.
3. Frequency is directly proportional to the square of temperature.
4. Frequency is directly proportional to the fourth power of temperature.
11.
Why does the intensity shown in the blackbody radiation graph decrease after its peak frequency is achieved?
1. Because after reaching the peak frequency, the photons created at a particular frequency are too many for energy intensity to continue to decrease.
2. Because after reaching the peak frequency, the photons created at a particular frequency are too few for energy intensity to continue to decrease.
3. Because after reaching the peak frequency, the photons created at a particular frequency are too many for energy intensity to continue to increase.
4. Because after reaching the peak frequency, the photons created at a particular frequency are too few for energy intensity to continue to increase.
12.
Shortly after the introduction of photography, it was found that photographic emulsions were more sensitive to blue and violet light than they were to red light. Explain why this was the case.
1. Blue-violet light contains greater amount of energy than red light.
2. Blue-violet light contains lower amount of energy than red light.
3. Both blue-violet light and red light have the same frequency but contain different amounts of energy.
4. Blue-violet light frequency is lower than the frequency of red light.
13.

Why is it assumed that a perfect absorber of light (like a blackbody) must also be a perfect emitter of light?

1. To achieve electrostatic equilibrium with its surroundings
2. To achieve thermal equilibrium with its surroundings
3. To achieve mechanical equilibrium with its surroundings
4. To achieve chemical equilibrium with its surroundings

#### 21.2Einstein and the Photoelectric Effect

14.
Light is projected onto a semi-conductive surface. If the intensity is held constant but the frequency of light is increased, what will happen?
1. As frequency is increased, electrons will stop being ejected from the surface.
2. As frequency is increased, electrons will begin to be ejected from the surface.
3. As frequency is increased, it will have no effect on the electrons being ejected as the intensity is the same.
4. As frequency is increased, the rate at which the electrons are being ejected will increase.
15.

Why is it important to consider what material to use when designing a light meter? Consider the worked example from Section 21-2 for assistance.

1. A light meter should contain material that responds only to high frequency light.
2. A light meter should contain material that responds to low frequency light.
3. A light meter should contain material that has high binding energy.
4. A light meter should contain a material that does not show any photoelectric effect.
16.

Why does overexposure to UV light often result in sunburn when overexposure to visible light does not? This is why you can get burnt even on a cloudy day.

1. UV light carries less energy than visible light and can penetrate our body.
2. UV light carries more energy than visible light, so it cannot break bonds at the cellular level.
3. UV light carries more energy than visible light and can break bonds at the cellular level.
4. UV light carries less energy than visible light and cannot penetrate the human body.
17.

If you pick up and shake a piece of metal that has electrons in it free to move as a current, no electrons fall out. Yet if you heat the metal, electrons can be boiled off. Explain both of these facts as they relate to the amount and distribution of energy involved with shaking the object as compared with heating it.

1. Thermal energy is added to the metal at a much higher rate than energy added due to shaking.
2. Thermal energy is added to the metal at a much lower rate than energy added due to shaking.
3. If the thermal energy added is below the binding energy of the electrons, they may be boiled off.
4. If the mechanical energy added is below the binding energy of the electrons, they may be boiled off.

#### 21.3The Dual Nature of Light

18.
In many macroscopic collisions, a significant amount of kinetic energy is converted to thermal energy. Explain why this is not a concern for Compton scattering.
1. Because, photons and electrons do not exist on the molecular level, all energy of motion is considered kinetic energy.
2. Because, photons exist on the molecular level while electrons do not exist on the molecular level, all energy of motion is considered kinetic energy.
3. Because, electrons exist on the molecular level while photons do not exist on the molecular level, all energy of motion is considered kinetic energy.
4. Because, photons and electrons exist on the molecular level, all energy of motion is considered kinetic energy.
19.

In what region of the electromagnetic spectrum will photons be most effective in accelerating a solar sail?

1. ultraviolet rays
2. infrared rays
3. X-rays
4. gamma rays
20.

True or false—Electron microscopes can resolve images that are smaller than the images resolved by light microscopes.

1. false
2. true
21.
How would observations of Compton scattering change if ultraviolet light were used in place of X-rays?
1. Ultraviolet light carries less energy than X-rays. As a result, Compton scattering would be easier to detect.
2. Ultraviolet light carries less energy than X-rays. As a result, Compton scattering would be more difficult to detect.
3. Ultraviolet light carries more energy than X-rays. As a result, Compton scattering would be easier to detect.
4. Ultraviolet light has higher energy than X-rays. As a result, Compton scattering would be more difficult to detect.

### Problems

#### 21.1Planck and Quantum Nature of Light

22.

How many X-ray photons per second are created by an X-ray tube that produces a flux of X-rays having a power of 1.00 W? Assume the average energy per photon is 75.0 keV.

1. 8.33 × 1015 photons
2. 9.1 × 107 photons
3. 9.1 × 108 photons
4. 8.33 × 1013 photons
23.

What is the frequency of a photon produced in a CRT using a 25.0-kV accelerating potential? This is similar to the layout as in older color television sets.

1. 6.04 × 10−48 Hz
2. 2.77 × 10−48 Hz
3. 3.02 × 1018 Hz
4. 6.04 × 1018 Hz

#### 21.2Einstein and the Photoelectric Effect

24.

What is the binding energy in eV of electrons in magnesium, if the longest-wavelength photon that can eject electrons is 337 nm?

1. 7.44 × 10−19 J
2. 7.44 × 10−49 J
3. 5.90 × 10−17 J
4. 5.90 × 10−19 J
25.

Photoelectrons from a material with a binding energy of 2.71 eV are ejected by 420-nm photons. Once ejected, how long does it take these electrons to travel 2.50 cm to a detection device?

1. 8.5 × 10−6 s
2. 3.5 × 10−7 s
3. 43.5 × 10−9 s
4. 8.5 × 10−8 s

#### 21.3The Dual Nature of Light

26.

What is the momentum of a 0.0100-nm-wavelength photon that could detect details of an atom?

1. 6.626 × 10−27 kg ⋅ m/s
2. 6.626 × 10−32 kg ⋅ m/s
3. 6.626 × 10−34 kg ⋅ m/s
4. 6.626 × 10-23 kg ⋅ m/s
27.

The momentum of light is exactly reversed when reflected straight back from a mirror, assuming negligible recoil of the mirror. Thus the change in momentum is twice the initial photon momentum. Suppose light of intensity 1.00 kW/m2 reflectsfrom a mirror of area 2.00 m2 each second. Using the most general form of Newton’s second law, what is the force on the mirror?

1. 1.33 × 10-5 N
2. 1.33 × 10−6 N
3. 1.33 × 10−7 N
4. 1.33 × 10−8 N

#### 21.3The Dual Nature of Light

28.

Our scientific understanding of light has changed over time. There is evidence to support the wave model of light, just as there is evidence to support the particle model of light.

1. Construct a demonstration that supports the wave model of light. Note—One possible method is to use a piece of aluminum foil, razor blade, and laser to demonstrate wave interference. Can you arrange these materials to create an effective demonstration? In writing, explain how evidence from your demonstration supports the wave model of light.
2. Construct a demonstration that supports the particle model of light. Note—One possible method is to use a negatively charged electroscope, zinc plate, and three light sources of different frequencies. A red laser, a desk lamp, and ultraviolet lamp are typically used. Can you arrange these materials to demonstrate the photoelectric effect? In writing, explain how evidence from your demonstration supports the particle model of light.