Deck 5: Matter Behaves Like Waves Quantum Physics

Question 1

As one approaches the bottom of a body of water, the circles shown in figure Q1.3 for water waves moving along the water's surface become increasingly vertically flattened ellipses. This means that the waves near the body's bottom are more (A) transverse or (B) longitudinal than those near the surface?

A) Transverse
B) Longitudinal

Answer 1

Longitudinal

Question 2

Imagine a series of mutually repelling ring magnets strung along a nearly frictionless horizontal rigid rod. If one jostles a magnet near one end of the rod, it can cause a wave of disturbance to move down the rod through the other magnets. Will this be a (A) transverse or (B) longitudinal wave?

A) Transverse wave
B) Longitudinal wave

Answer 2

Longitudinal wave

Question 3

As a sinusoidal wave's wavenumber increases, the wave's wavelength (in a non-dispersive medium)

A) Increases.
B) Decreases.
C) Does not change.

Answer 3

Decreases.

Question 4

A sinusoidal wave's angular frequency is (A) larger, (B) smaller, or (C) the same as its frequency in cycles/s.

A) Large
B) Smaller
C) The same as its frequency in cycles/s.

Question 5

Equation $|\vec{v}|=\frac{\omega}{k}=\frac{\lambda}{T}=\lambda f$ implies that a sinusoidal wave's phase speed depends on its wavelength.

Question 6

Consider wiggle formula $w(t, x)=f(\mathrm{bx}+\mathrm{ct})$ for a transverse wave, where $b$ and $c$ are constants and $f()$ is some arbitrary function. Is this a traveling wave model? If so, in what direction does it travel?

A) In the $+x$ direction.
B) In the $-x$ direction.
C) The wave does not move.
D) In the $y$ or $z$ direction because the wave is transverse.

Question 7

In a specific non-dispersive medium, a sinusoidal wave's angular frequency is proportional to its wavenumber.

Question 8

In a specific non-dispersive medium, a sinusoidal wave's period is proportional to its wavelength.

Question 9

If one sound is $20 \mathrm{~dB}$ louder than another sound, its intensity is

A) 2 times greater.
B) 20 times greater.
C) 100 times greater.
D) 200 times greater.
E) We need to know the actual sound level: $30 \mathrm{db}$ to $50 \mathrm{db}$ represents a different factor of intensity increase than 60 $\mathrm{db}$ to $80 \mathrm{db}$ (for example).

Question 10

A linear traveling wave can be partially reflected when it encounters another linear traveling wave.

Question 11

A sound wave traveling in air hits the surface of a body of water. Is the reflected wave (A) inverted or (B) upright? (Make a guess.)

A) Inverted
B) Upright

Question 12

A sound wave traveling in air hits the surface of a body of water. The reflection will be total.

Question 13

Imagine that the wave shown below moves right along a stretched string. It meets and passes through one of the left-going waves provided in the choices. For which choice is there an instant where the string is flat?

A) A
B) B
C) C
D) D
E) None of the above

Question 14

Consider the right-going wave and the possible left-going waves displayed in problem Q2T.3. For which of the choices will there be an instant where the combined wave is a rectangular wave as shown below?

A) A
B) B
C) C
D) D
E) None of the above

Question 15

Suppose we create a traveling compression wave in a spring that has one end fixed. When the wave reflects from the fixed end, it will be inverted (that is, compression will become rarefaction and vice versa).

Question 16

Suppose you are near one end of a 150-m-long cylindrical tunnel open to the air on both ends. If you give a shout, you might hear an echo.

Question 17

If you face a cliff and give a shout, you will hear an echo. Are the sound waves of the echo inverted (A) or upright (B) compared to the waves of your original shout?

A) Inverted
B) Upright

Question 18

The frequencies of the normal modes of a string that is free at both ends are the same as those of a string that is fixed at both ends.

Question 19

A sinusoidal standing sound wave inside a tube that is open at both ends must fit between the tube's ends

A) An integer number of wavelengths.
B) An integer number of half-wavelengths.
C) An integer number of quarter-wavelengths
D) An odd-integer number of half-wavelengths.
E) An odd-integer number of quarter-wavelengths.

Question 20

The normal mode of a resonating system is sinusoidally disturbed at a frequency $f$ . Assume that $\gamma<<f_{0}$ , where $f_{0}$ is the normal mode's natural frequency.

-(a) What is the amplitude of the normal mode's oscillation compared to its amplitude $A_{0}$ in the limit that the disturbance frequency goes to zero if $f$ is about $1.4 f_{0}$ ?

A) Roughly zero
B) Roughly $A_{0} / 30$
C) Roughly $A_{0} / 1.4$
D) Roughly $A_{0}$
E) Roughly $1.4 \mathrm{~A}_{0}$
F) Roughly $30 A_{0}$
G) Other (specify)

Question 21

The normal mode of a resonating system is sinusoidally disturbed at a frequency $f$ . Assume that $\gamma<<f_{0}$ , where $f_{0}$ is the normal mode's natural frequency.

-(b) If $f$ is about $30 f_{0}$ ?

A) Roughly zero
B) Roughly $A_{0} / 30$
C) Roughly $A_{0} / 1.4$
D) Roughly $A_{0}$
E) Roughly $1.4 \mathrm{~A}_{0}$
F) Roughly $30 A_{0}$
G) Other (specify)

Question 22

Two stretched strings with the same length but different tensions are both resonating at the same frequency. Which string has the greater number of antinodes?

A) The string with the larger tension.
B) The string with the smaller tension.
C) Both must have the same number of antinodes.

Question 23

In chapter Q1, we noted that the speed of sound in air depends on the air's temperature (increasing as the square root of the air temperature). Suppose a flute player tunes a flute that has been sitting in a cold automobile. As the flute warms up to room temperature, does it go sharp (A) or flat (B)?

A) Sharp
B) Flat

Question 24

The period $T$ of the fundamental mode of the air in a pipe open at one end and closed at the other is equal to what multiple or fraction of the time $\Delta t$ required for a sound wave to travel from one end of the tube to the other?

A) $T=\Delta t / 4$
B) $T=\Delta t / 2$
C) $T=\Delta t$
D) $T=2 \Delta t$
E) $T=4 \Delta t$

Question 25

A certain organ pipe is open at both ends. Another pipe of the same length is open at one end and closed at the other. Which will have the lower pitch?

A) The pipe open at both ends.
B) The pipe closed at one end.
C) Both will have the same pitch.
D) It depends on the pipes' diameters.

Question 26

Waves from two slits $S$ and $Q$ will destructively interfere and cancel at a point $P$ if the distance between $P$ and $S$ is larger than the distance between $P$ and $Q$ by

A) $\lambda$
B) $n \lambda$ (where $n$ is an integer)
C) $\frac{1}{2} n \lambda$ (where $n$ is an integer)
D) $\left(n+\frac{1}{2}\right) \lambda$ (where $n$ is an integer)
E) Other (specify)

Question 27

Consider a two-slit interference experiment like the one shown in figure Q3.7b. The distance between adjacent bright spots in the interference pattern on the screen ,


-The wavelength of the light increases.

A) increases
B) decreases
C) remains the same

Question 28

Consider a two-slit interference experiment like the one shown in figure Q3.7b. The distance between adjacent bright spots in the interference pattern on the screen ,


-The spacing between the slits increases.

A) increases
B) decreases
C) remains the same

Question 29

Consider a two-slit interference experiment like the one shown in figure Q3.7b. The distance between adjacent bright spots in the interference pattern on the screen ,


- The intensity of the light increases.

A) increases
B) decreases
C) remains the same

Question 30

Consider a two-slit interference experiment like the one shown in figure Q3.7b. The distance between adjacent bright spots in the interference pattern on the screen ,


-The width of the slits increases.

A) increases
B) decreases
C) remains the same

Question 31

Consider a two-slit interference experiment like the one shown in figure Q3.7b. The distance between adjacent bright spots in the interference pattern on the screen ,


-The distance between the slits and the screen increases.

A) increases
B) decreases
C) remains the same

Question 32

Consider a two-slit interference experiment like the one shown in figure Q3.7b. The distance between adjacent bright spots in the interference pattern on the screen ,


-The value of $n$ increases (careful!).

A) increases
B) decreases
C) remains the same

Question 33

Imagine that sound waves with a certain definite wavelength flow through a partially open sliding door. If the door is closed somewhat further (but not shut entirely), the angle through which the sound waves are diffracted

A) Decreases.
B) Increases.
C) Remains the same.
D) Depends on quantities not specified (explain).

Question 34

Imagine that sound waves with a certain definite wavelength flow through a partially open sliding door. If the wavelength of the waves increases, the angle through which the sound waves are diffracted

A) Decreases.
B) Increases.
C) Remains the same.
D) Depends on quantities not specified (explain).

Question 35

Line waves with wavelength $\lambda$ going through a slit with width a will be diffracted into circular waves with approximately equal amplitude in all forward directions

A) Always
B) Never
C) Only if $\lambda \gg>a$
D) Only if $a>>\lambda$
E) Only if $a=\lambda$

Question 36

If the two slits in a two-slit interference experiment are so far apart that their diffraction patterns do not overlap, the pattern displayed is consistent with a particle model of light.

Question 37

Consider an experiment where we send monochromatic light to a distant screen through a single narrow slit. The distance between adjacent dark fringes in the diffraction pattern displayed on the screen

- The wavelength of the light increases.

A) increases
B) decreases
C) remains the same

Question 38

Consider an experiment where we send monochromatic light to a distant screen through a single narrow slit. The distance between adjacent dark fringes in the diffraction pattern displayed on the screen

-The intensity of the light increases.

A) increases
B) decreases
C) remains the same

Question 39

Consider an experiment where we send monochromatic light to a distant screen through a single narrow slit. The distance between adjacent dark fringes in the diffraction pattern displayed on the screen

-The width of the slit increases.

A) increases
B) decreases
C) remains the same

Question 40

Consider an experiment where we send monochromatic light to a distant screen through a single narrow slit. The distance between adjacent dark fringes in the diffraction pattern displayed on the screen

- The distance between the slit and the screen increases.

A) increases
B) decreases
C) remains the same

Question 41

Consider an experiment where we send monochromatic light to a distant screen through a single narrow slit. The distance between adjacent dark fringes in the diffraction pattern displayed on the screen

-We look at fringes farther from the central maximum.

A) increases
B) decreases
C) remains the same

Question 42

In the region where their beams overlap, two car headlights will create a clear interference pattern on a distant screen.

Question 43

If we shine white light through two slits onto a distant screen, we will see a clear interference pattern.

Question 44

Imagine we have an adjustable slit that we can make wider or narrower. If we shine light of a fixed intensity on the slit, and then crank the slit so its width decreases (while keeping other things the same), will the light at the center of the central peak on the display screen?

A) Remain the same
B) Get brighter
C) Get dimmer

Question 45

Eagles and other predatory birds have very sharp eyesight. The pupil of an eagle's eye is roughly twice the size of a human's under similar (daylight) conditions. A friend claims to have read that an eagle's eye has 8 times the resolving power of a human eye in broad daylight. This is physically impossible.

Question 46

With an optically perfect 200-power telescope with a 1.5-inch-diameter tube, you can resolve objects roughly how many times closer together than you could with your naked eye? (Choose the closest answer.)

A) 200 times
B) 100 times
C) 20 times
D) 5 times
E) No better at all

Question 47

Sunlight falling on a spaceship in a vacuum will cause the spaceship to become a bit positively charged.

Question 48

In the apparatus shown in figure Q4.1a, the value displayed by the ammeter is proportional to

A) The rate at which electrons emerge from the cathode.
B) The average kinetic energy of the ejected electrons.
C) The maximum kinetic energy of the ejected electrons.
D) Both A and C.

Question 49

For experiments involving the setup shown in figure Q4.1a, which of the following possible results (if seen) about the value displayed by the ammeter would probably not be consistent with the wave model of light?

A) It is zero for some time after light starts shining.
B) It increases as the light's intensity increases.
C) It varies as the light's wavelength changes.
D) It is zero if the wavelength is larger than a certain value.

Question 50

In the apparatus shown in figure Q4.1b, the final value displayed by the voltmeter is proportional to

A) The rate at which electrons emerge from the cathode.
B) The average kinetic energy of the ejected electrons.
C) The maximum kinetic energy of the ejected electrons.
D) Both A and C.

Question 51

For experiments involving the setup shown in figure $\mathrm{Q} 4.1 \mathrm{~b}$ , which of the following possible results (if seen) regarding the final value displayed by the voltmeter would probably not be consistent with the wave model of light?

(b) Metallic plate (cathode)

A) It increases as the light's intensity increases.
B) It is independent of the light's intensity.
C) It varies as the light's wavelength changes.
D) It increases as the rate of electron ejection increases.

Question 52

In experiments involving the setup shown in figure Q4.1b, the value that the voltmeter displays increases for a short period of time after light starts shining on the cathode, but then quickly settles down to a fixed value. Why?

A) The cathode eventually stops emitting electrons.
B) The kinetic energy of ejected electrons starts out small but quickly reaches a maximum value.
C) The charge difference between the cathode and anode is initially small but with time becomes so large that no electron from the cathode can make it to the anode.
D) The cathode eventually runs out of electrons to emit.
E) Some other explanation (describe).

Question 53

In an experiment involving the apparatus shown in figure Q4.1b, suppose that after shining light on the cathode long enough that the voltmeter settles down to a fixed value, we suddenly cut off the light. If the voltmeter is truly ideal, what happens to the value displayed?

A) It immediately drops to zero.
B) It slowly decays to zero.
C) It remains fixed.
D) It does something else. (Describe what.)

Question 54

A beam of light $P$ has twice the wavelength but the same intensity as beam $Q$ . The number of photons that hit a given area in a given time when it is illuminated by beam $P$ is (A) twice, (B) the same, or (C) one-half of the number that hit when the area is illuminated by beam $Q$ ?

A) Twice}
B) The Same
C) One-half of the number that hit

Question 55

Though this would be tricky to do in practice, suppose we could increase the frequency of light illuminating the cathode of the apparatus shown in figure Q4.1a while holding the intensity of that light constant. What would Einstein's photon model predict would happen to the value displayed by the ammeter as the frequency increases? (Assume that the light's frequency is always above the cathode's cutoff frequency.)

A) It should increase.
B) It should remain the same.
C) It should decrease.
D) It might vary in a complicated way.

Question 56

The work function $W$ for copper is $4.65 \mathrm{eV}$ . Visible light will dislodge electrons from a copper surface.

Question 57

If you want to design a phototube that is able to respond to all visible light wavelengths, what should its cathode's work function be?

A) Below $1.77 \mathrm{eV}$
B) Any value between $1.77 \mathrm{eV}$ and $3.1 \mathrm{eV}$
C) Some specific value between $1.77 \mathrm{eV}$ and $3.1 \mathrm{eV}$
D) Above $3.1 \mathrm{eV}$
E) Some other value or range (specify)

Question 58

If you want to design a phototube that ignores all visible light, what should its cathode's work function be?

A) Below $1.77 \mathrm{eV}$
B) Any value between $1.77 \mathrm{eV}$ and $3.1 \mathrm{eV}$
C) Some specific value between $1.77 \mathrm{eV}$ and $3.1 \mathrm{eV}$
D) Above $3.1 \mathrm{eV}$
E) Some other value or range (specify)

Question 59

Violet light with a wavelength of $430 \mathrm{~nm}$ falls on a sodium plate $(W=2.75 \mathrm{eV})$ and a potassium plate $(W=$ $2.30 \mathrm{eV})$ . Which of of the following statements is true?

A) Both plates emit electrons, but those emitted by the sodium plate have the larger kinetic energy.
B) Both plates emit electrons, but those emitted by the potassium plate have the larger kinetic energy.
C) Only the sodium plate emits electrons.
D) Only the potassium plate emits electrons.
E) Neither plate emits electrons.

Question 60

A long-wavelength photon, because it is larger, carries more total energy than a short-wavelength photon.

Question 61

Einstein's photon model is consistent with the results of two-slit interference experiments involving light.

Question 62

Consider a beam of free particles with a certain speed $|\vec{v}|$ . If we double this speed, what happens to the beam's de Broglie wavelength?

A) It increases by a factor of 2 .
B) It increases by a factor of $2^{1 / 2}$ .
C) It remains the same.
D) It decreases by a factor of $2^{1 / 2}$ .
E) It decreases by a factor of 2 .

Question 63

Consider a beam of free particles that each have a certain (nonrelativistic) kinetic energy $K$ . If we double this kinetic energy, what happens to the beam's wavelength?

A) It increases by a factor of 2 .
B) It increases by a factor of $2^{1 / 2}$ .
C) It remains the same.
D) It decreases by a factor of $2^{1 / 2}$ .
E) It decreases by a factor of 2.

Question 64

Imagine that in a Davisson-Germer-type experiment we shine a beam of electrons on a nickel crystal perpendicular to the crystal face and find that we get enhanced scattering at an angle of $50^{\circ}$ . If we double the electrons' kinetic energy,
-(a) the angle of enhanced scattering will (A) increase, (B) decrease, or (C) remain constant,

Question 65

Imagine that in a Davisson-Germer-type experiment we shine a beam of electrons on a nickel crystal perpendicular to the crystal face and find that we get enhanced scattering at an angle of $50^{\circ}$ . If we double the electrons' kinetic energy,
-(b) by a factor (A) a bit larger than, (B) a bit less than, or (C) equal to

Question 66

Imagine that in a Davisson-Germer-type experiment we shine a beam of electrons on a nickel crystal perpendicular to the crystal face and find that we get enhanced scattering at an angle of $50^{\circ}$ . If we double the electrons' kinetic energy,
-(c) (A) 1 (B) $2^{1 / 2}$ , or (C) 2

Question 67

Imagine that we shine a beam of electrons with a de Broglie wavelength of $0.1 \mathrm{~nm}$ through a pair of slits that have been miraculously constructed to be only $10 \mathrm{~nm}$ apart. What will be the order of magnitude of the distance between bright spots of the interference pattern displayed on a fluorescent screen placed $1 \mathrm{~m}$ from the slits?

A) $1 \mathrm{~cm}$
B) $1 \mathrm{~mm}$
C) $0.1 \mathrm{~mm}$
D) $10 \mathrm{~m}$
E) $1 \mu \mathrm{m}$

Question 68

To create an interference pattern, a quanton beam's de Broglie wavelength must be larger than an individual quanton.

Question 69

If the value of $h$ were bigger, it would be easier to display quanton interference effects.

Question 70

Consider the experimental evidence we have discussed in the past few chapters. Classify the following experimental results according to the following scheme: For the quantons in question, the results:

- When light goes through a slit, the beam broadens somewhat, and if it is projected on a screen, one can see bright and dark fringes on the slit image.

Question 71

Consider the experimental evidence we have discussed in the past few chapters. Classify the following experimental results according to the following scheme: For the quantons in question, the results:

- When light shines on a metal surface, electrons are ejected from the surface.

Question 72

Consider the experimental evidence we have discussed in the past few chapters. Classify the following experimental results according to the following scheme: For the quantons in question, the results:

- The number of electrons ejected from a metal surface depends directly on the intensity of the light shining on that metal surface.

Question 73

Consider the experimental evidence we have discussed in the past few chapters. Classify the following experimental results according to the following scheme: For the quantons in question, the results:

-The maximum kinetic energy of electrons ejected from a metal surface depends on the frequency of the light shining on the surface, and not on the intensity.

Question 74

Consider the experimental evidence we have discussed in the past few chapters. Classify the following experimental results according to the following scheme: For the quantons in question, the results:

-When light shines on a surface, at least a few electrons seem to get ejected virtually as soon as the surface is illuminated, even if the light is extremely dim.

Question 75

Consider the experimental evidence we have discussed in the past few chapters. Classify the following experimental results according to the following scheme: For the quantons in question, the results:

-An electron beam shining on a nickel crystal is preferentially reflected in certain directions instead of being scattered uniformly in all directions.

Question 76

Consider the experimental evidence we have discussed in the past few chapters. Classify the following experimental results according to the following scheme: For the quantons in question, the results:

-Light that goes through two narrow, closely spaced slits in an opaque barrier and then falls on a screen creates a pattern of multiple bright spots on the screen.

Question 77

Consider the experimental evidence we have discussed in the past few chapters. Classify the following experimental results according to the following scheme: For the quantons in question, the results:

- When dim light falls on a photomultiplier, the latter produces discrete electric pulses at random times.

Question 78

Consider the experimental evidence we have discussed in the past few chapters. Classify the following experimental results according to the following scheme: For the quantons in question, the results:

-A rapidly moving electron leaves a track in a bubble chamber photograph.

Question 79

Consider the experimental evidence we have discussed in the past few chapters. Classify the following experimental results according to the following scheme: For the quantons in question, the results:

- Photons sent one at a time through two slits appear individually to hit a detector array at random positions, but statistically fall into a two-slit interference pattern.

Question 80

Figure Q5.9 displays a sample simulated interference pattern for a quanton-at-a-time interference experiment (the graph shows the number of quanton detection events versus position) followed by five interference patterns labeled A through E. Each table row below describes a set of parameters that will create one of the displayed patterns (the first row shows the parameters that display the "Sample" pattern). The slit separation stated is a center-to-center distance. The table rows are organized so that each set of parameters differs from the previous one by a change in only one value. The "Detectors" column refers to whether there are proximity detectors operating at the slits. Your task is to write the appropriate letter in the table's right-most column. You might use some letters more than once. (Thanks to David Tanenbaum and Jason Evans for developing this exercise.)


A.

B.

C.

D.

E.