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Test Prep

Multiple Choice

21.1Planck and Quantum Nature of Light

1.

A perfect blackbody is a perfect absorber of energy transferred by what method?

1. conduction
2. convection
3. induction
2.

Which of the following is a physical entity that is quantized?

1. electric charge of an ion
2. frequency of a sound
3. speed of a car
3.

Find the energy in joules of photons of radio waves that leave an FM station that has a 90.0-MHz broadcast frequency.

1. 1.8 × 10−25 J
2. 1.11 × 10−25 J
3. 7.1 × 10−43 J
4. 5.96 × 10-26 J
4.

Which region of the electromagnetic spectrum will provide photons of the least energy?

1. infrared light
3. ultraviolet light
4. X-rays
5.
A hot, black coffee mug is sitting on a kitchen table in a dark room. Because it cannot be seen, one assumes that it is not emitting energy in the form of light. Explain the fallacy in this logic.
1. Not all heat is in the form of light energy.
2. Not all light energy falls in the visible portion of the electromagnetic spectrum.
3. All heat is in the form of light energy.
4. All light energy falls in the visible portion of the electromagnetic spectrum.
6.

Given two stars of equivalent size, which will have a greater temperature: a red dwarf or a yellow dwarf? Explain. Note—Our sun is considered a yellow dwarf.

1. a yellow dwarf, because yellow light has lower frequency
2. a red dwarf, because red light has lower frequency
3. a red dwarf, because red light has higher frequency
4. a yellow dwarf, because yellow light has higher frequency

21.2Einstein and the Photoelectric Effect

7.

What is a quantum of light called?

1. electron
2. neutron
3. photon
4. proton
8.
Which of the following observations from the photoelectric effect is not a violation of classical physics?
1. Electrons are ejected immediately after impact from light.
2. Light can eject electrons from a semi-conductive material.
3. Light intensity does not influence the kinetic energy of ejected electrons.
4. No electrons are emitted if the light frequency is too low.
9.
If $5eV$ of energy is supplied to an electron with a binding energy of $2.3eV$, with what kinetic energy will the electron be launched?
1. $2.3eV$
2. $7.3eV$
3. $11.5eV$
4. $2.7eV$
10.

Which of the following terms translates to light-producing voltage?

1. photoelectric
2. quantum mechanics
3. photoconductive
4. photovoltaic
11.
Why is high frequency EM radiation considered more dangerous than long wavelength EM radiation?
1. Long wavelength EM radiation photons carry less energy and therefore have greater ability to disrupt materials through the photoelectric effect.
2. Long wavelength EM radiation photons carry more energy and therefore have greater ability to disrupt materials through the photoelectric effect.
3. High frequency EM radiation photons carry less energy and therefore have lower ability to disrupt materials through the photoelectric effect.
4. High frequency EM radiation photons carry more energy and therefore have greater ability to disrupt materials through the photoelectric effect.
12.
Why are UV, X-rays, and gamma rays considered ionizing radiation?
1. UV, X-rays, and gamma rays are capable of ejecting photons from a surface.
2. UV, X-rays, and gamma rays are capable of ejecting neutrons from a surface.
3. UV, X-rays, and gamma rays are capable of ejecting protons from a surface.
4. UV, X-rays, and gamma rays are capable of ejecting electrons from a surface.

21.3The Dual Nature of Light

13.

What two particles interact in Compton scattering?

1. photon and electron
2. proton and electron
3. neutron and electron
4. proton and neutron
14.

What is the momentum of a 500-nm photon?

1. 8.35 × 10−26 kg ⋅ m/s
2. 3.31 × 10−40 kg ⋅ m/s
3. 7.55 × 1026 kg ⋅ m/s
4. 1.33 × 10-27 kg ⋅ m/s
15.

The conservation of what fundamental physics principle is behind the technology of solar sails?

1. charge
2. mass
3. momentum
4. angular momentum
16.

Terms like frequency, amplitude, and period are tied to what component of wave-particle duality?

1. neither the particle nor the wave model of light
2. both the particle and wave models of light
3. the particle model of light
4. the wave model of light
17.

Why was it beneficial for Compton to scatter electrons using X-rays and not another region of light like microwaves?

1. because X-rays are more penetrating than microwaves
2. because X-rays have lower frequency than microwaves
3. because microwaves have shorter wavelengths than X-rays
4. because X-rays have shorter wavelength than microwaves

21.1Planck and Quantum Nature of Light

18.
Scientists once assumed that all frequencies of light were emitted with equal probability. Explain what the blackbody radiation curve would look like if this were the case.
1. The blackbody radiation curve would look like a circular path.
2. The blackbody radiation curve would look like an elliptical path.
3. The blackbody radiation curve would look like a vertical line.
4. The blackbody radiation curve would look like a horizontal line.
19.

Because there are more gradations to high frequency radiation than low frequency radiation, scientists also thought it possible that a curve titled the ultraviolet catastrophe would occur. Explain what the blackbody radiation curve would look like if this were the case.

1. The curve would steadily increase in intensity with increasing frequency.
2. The curve would steadily decrease in intensity with increasing frequency.
3. The curve would be much steeper than in the blackbody radiation graph.
4. The curve would be much flatter than in the blackbody radiation graph.
20.

Energy provided by a light exists in the following quantities: 150 J, 225 J, 300 J. Define one possible quantum of energy and provide an energy state that cannot exist with this quantum.

1. 65 J; 450 J cannot exist
2. 70 J; 450 J cannot exist
3. 75 J; 375 J cannot exist
4. 75 J; 100 J cannot exist
21.
Why is Planck’s recognition of quantum particles considered the dividing line between classical and modern physics?
1. Planck recognized that energy is quantized, which was in sync with the classical physics concepts but not in agreement with modern physics concepts.
2. Planck recognized that energy is quantized, which was in sync with modern physics concepts but not in agreement with classical physics concepts.
3. Prior to Planck’s hypothesis, all the classical physics calculations were valid for subatomic particles, but quantum physics calculations were not valid.
4. Prior to Planck’s hypothesis, all the classical physics calculations were not valid for macroscopic particles, but quantum physics calculations were valid.
22.

How many 500-mm microwave photons are needed to supply the 8 kJ of energy necessary to heat a cup of water by 10 degrees Celsius?

1. 8.05 × 1028 photons
2. 8.05 × 1026 photons
3. 2.01 × 1026 photons
4. 2.01 × 1028 photons
23.

What is the efficiency of a 100-W, 550-nm lightbulb if a photometer finds that 1 × 1020 photons are emitted each second?

1. 101 percent
2. 72 percent
3. 18 percent
4. 36 percent
24.
Rank the following regions of the electromagnetic spectrum by the amount of energy provided per photon: gamma, infrared, microwave, ultraviolet, radio, visible, X-ray.
1. radio, microwave, infrared, visible, ultraviolet, X-ray, gamma
2. radio, infrared, microwave, ultraviolet, visible, X-ray, gamma
3. radio, visible, microwave, infrared, ultraviolet, X-ray, gamma
4. radio, microwave, infrared, visible, ultraviolet, gamma, X-ray
25.
Why are photons of gamma rays and X-rays able to penetrate objects more successfully than ultraviolet radiation?
1. Photons of gamma rays and X-rays carry with them less energy.
2. Photons of gamma rays and X-rays have longer wavelengths.
3. Photons of gamma rays and X-rays have lower frequencies.
4. Photons of gamma rays and X-rays carry with them more energy.

21.2Einstein and the Photoelectric Effect

26.

According to wave theory, what is necessary to eject electrons from a surface?

1. Enough energy to overcome the binding energy of the electrons at the surface
2. A frequency that is higher than that of the electrons at the surface
3. Energy that is lower than the binding energy of the electrons
4. A very small number of photons
27.

What is the wavelength of EM radiation that ejects 2.00-eV electrons from calcium metal, given that the binding energy is 2.71 eV?

1. 16.1 × 105 m
2. 6.21 × 10−5 m
3. 9.94 × 10−26 m
4. 2.63 × 10-7 m
28.

Find the wavelength of photons that eject 0.100-eV electrons from potassium, given that the binding energy is 2.24 eV.

1. 6.22 × 10−7 m
2. 5.92 × 10−5 m
3. 1.24 × 10−5 m
4. 5.31 × 10-7 m
29.
How do solar cells utilize the photoelectric effect?
1. A solar cell converts all photons that it absorbs to electrical energy using the photoelectric effect.
2. A solar cell converts all electrons that it absorbs to electrical energy using the photoelectric effect.
3. A solar cell absorbs the photons with energy less than the energy gap of the material of the solar cell and converts it to electrical energy using the photoelectric effect.
4. A solar cell absorbs the photons with energy greater than the energy gap of the material of the solar cell and converts it to electrical energy using the photoelectric effect.
30.
Explain the advantages of the photoelectric effect to other forms of energy transformation.
1. The photoelectric effect is able to work on the Sun’s natural energy.
2. The photoelectric effect is able to work on energy generated by burning fossil fuels.
3. The photoelectric effect can convert heat energy into electrical energy.
4. The photoelectric effect can convert electrical energy into light energy.

21.3The Dual Nature of Light

31.
Upon collision, what happens to the frequency of a photon?
1. The frequency of the photon will drop to zero.
2. The frequency of the photon will remain the same.
3. The frequency of the photon will increase.
4. The frequency of the photon will decrease.
32.
How does the momentum of a photon compare to the momentum of an electron of identical energy?
1. Momentum of the photon is greater than the momentum of an electron.
2. Momentum of the photon is less than the momentum of an electron.
3. Momentum of the photon is equal to the momentum of an electron.
4. Momentum of the photon is zero due to zero rest mass but the momentum of an electron is finite.
33.

A 500-nm photon strikes an electron and loses 20 percent of its energy. What is the new momentum of the photon?

1. 4.24 × 10−27 kg ⋅ m/s
2. 3.18 × 10−27 kg ⋅ m/s
3. 2.12 × 10−27 kg ⋅ m/s
4. 1.06 × 10−27 kg ⋅ m/s
34.

A 500-nm photon strikes an electron and loses 20 percent of its energy. What is the speed of the recoiling electron?

1. 7.18 × 105 m/s
2. 6.18 × 105 m/s
3. 5.18 × 105 m/s
4. 4.18 × 105 m/s
35.

When a photon strikes a solar sail, what is the direction of impulse on the photon?

1. parallel to the sail
2. perpendicular to the sail
3. tangential to the sail
4. opposite to the sail
36.
What is a fundamental difference between solar sails and sails that are used on sailboats?
1. Solar sails rely on disorganized strikes from light particles, while sailboats rely on disorganized strikes from air particles.
2. Solar sails rely on disorganized strikes from air particles, while sailboats rely on disorganized strikes from light particles.
3. Solar sails rely on organized strikes from air particles, while sailboats rely on organized strikes from light particles.
4. Solar sails rely on organized strikes from light particles, while sailboats rely on organized strikes from air particles.
37.

The wavelength of a particle is called the de Broglie wavelength, and it can be found with the equation $p=\frac{h}{\lambda }$.

Yes or no—Can the wavelength of an electron match that of a proton?

1. Yes, a slow-moving electron can achieve the same momentum as a proton.
2. No, a fast-moving electron cannot achieve the same momentum, and hence the same wavelength, as a slow-moving proton.
3. No, an electron can achieve the same momentum, and hence but not the same wavelength, as a proton.
4. Yes, a fast-moving electron can achieve the same momentum, and hence have the same wavelength, as a slow-moving proton.
38.
Large objects can move with great momentum. Why then is it difficult to see their wave-like nature?
1. Their wavelength is equal to the object’s size.
2. Their wavelength is very small compared to the object’s size.
3. Their wavelength is very large compared to the object’s size.
4. Their frequency is very small compared to the object’s size.

Extended Response

21.1Planck and Quantum Nature of Light

39.
Some television tubes are CRTs. They use an approximately $30-kV$ accelerating potential to send electrons to the screen, where the electrons stimulate phosphors to emit the light that forms the pictures we watch. Would you expect X-rays also to be created? Explain.
1. No, because the full spectrum of EM radiation is not emitted at any temperature.
2. No, because the full spectrum of EM radiation is not emitted at certain temperatures.
3. Yes, because the full spectrum of EM radiation is emitted at any temperature.
4. Yes, because the full spectrum of EM radiation is emitted at certain temperatures.
40.
If Planck’s constant were large, say $1034$ times greater than it is, we would observe macroscopic entities to be quantized. Describe the motion of a child’s swing under such circumstances.
1. The child would not be able to swing with particular energies.
2. The child could be released from any height.
3. The child would be able to swing with constant velocity.
4. The child could be released only from particular heights.
41.

What is the accelerating voltage of an X-ray tube that produces X-rays with the shortest wavelength of 0.0103 nm?

1. 1.21 × 1010 V
2. 2.4 × 105 V
3. 3.0 × 10−33 V
4. 1.21 × 105 V
42.
Patients in a doctor’s office are rightly concerned about receiving a chest X-ray. Yet visible light is also a form of electromagnetic radiation and they show little concern about sitting under the bright lights of the waiting room. Explain this discrepancy.
1. X-ray photons carry considerably more energy so they can harm the patients.
2. X-ray photons carry considerably less energy so they can harm the patients.
3. X-ray photons have considerably longer wavelengths so they cannot harm the patients.
4. X-ray photons have considerably lower frequencies so they can harm the patients.

21.2Einstein and the Photoelectric Effect

43.
When increasing the intensity of light shining on a metallic surface, it is possible to increase the current created on that surface. Classical theorists would argue that this is evidence that intensity causes charge to move with a greater kinetic energy. Argue this logic from the perspective of a modern physicist.
1. The increased intensity increases the number of ejected electrons. The increased current is due to the increase in the number of electrons.
2. The increased intensity decreases the number of ejected electrons. The increased current is due to the decrease in the number of electrons ejected.
3. The increased intensity does not alter the number of electrons ejected. The increased current is due to the increase in the kinetic energy of electrons.
4. The increased intensity alters the number of electrons ejected, but an increase in the current is due to an increase in the kinetic energy of electrons.
44.
What impact does the quantum nature of electromagnetic radiation have on the understanding of speed at the particle scale?
1. Speed must also be quantized at the particle scale.
2. Speed will not be quantized at the particle scale.
3. Speed must be zero at the particle scale.
4. Speed will be infinite at the particle scale.
45.

A 500 nm photon of light strikes a semi-conductive surface with a binding energy of 2 eV. With what velocity will an electron be emitted from the semi-conductive surface?

1. 8.38 × 105 m/s
2. 9.33 × 105 m/s
3. 3 × 108 m/s
4. 4.11 × 105 m/s
46.

True or false—Treating food with ionizing radiation helps keep it from spoiling.

1. true
2. false

21.3The Dual Nature of Light

47.
When testing atomic bombs, scientists at Los Alamos recognized that huge releases of energy resulted in problems with power and communications systems in the area surrounding the blast site. Explain the possible tie to Compton scattering.
1. The release of light energy caused large-scale emission of electrons.
2. The release of light energy caused large-scale emission of protons.
3. The release of light energy caused large-scale emission of neutrons.
4. The release of light energy caused large-scale emission of photons.
48.

Sunlight above the Earth’s atmosphere has an intensity of 1.30 kW/m2 . If this is reflected straight back from a mirror that has only a small recoil, the light’s momentum is exactly reversed, giving the mirror twice the incident momentum. If the mirror were attached to a solar sail craft, how fast would the craft be moving after 24 hr? Note—The average mass per square meter of the craft is 0.100 kg.

1. 8.67 × 10−5 m/s2
2. 8.67 × 10−6 m/s2
3. 94.2 m/s
4. 7.49 m/s
49.

Consider the counter-clockwise motion of LightSail-1 around Earth. When will the satellite move the fastest?

Figure 21.16
1. point A
2. point B
3. point C
4. point D
50.
What will happen to the interference pattern created by electrons when their velocities are increased?
1. There will be more zones of constructive interference and fewer zones of destructive interference.
2. There will be more zones of destructive interference and fewer zones of constructive interference.
3. There will be more zones of constructive and destructive interference.
4. There will be fewer zones of constructive and destructive interference.