Physics

# Extended Response

PhysicsExtended Response

### 21.1Planck and Quantum Nature of Light

67.

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.
68.
If Planck’s constant were large, say $10 Superscript 34$ 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.
69.

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
70.
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

71.
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.
72.
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.
73.

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
74.

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

1. true
2. false

### 21.3The Dual Nature of Light

75.
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.
76.

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
77.

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

1. point A
2. point B
3. point C
4. point D
78.
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.
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