Deck 37: Quanta of Light

Question 1

According to classical wave theory, of the possible resonant modes associated with a cavity, the wavelength has

A) a maximum value but no minimum.
B) a minimum value but no maximum.
C) both a maximum and a minimum (at different values).
D) None of the previous responses is correct.

Answer 1

a maximum value but no minimum.

Question 2

Max Planck postulated that the atoms comprising a cavity could resonate only

A) at discrete values of frequency.
B) at discrete values of wavelength.
C) at discrete values of energy.
D) All the atoms must be from a particular element to have a cavity resonate.
E) All of the above are correct.

Answer 2

at discrete values of energy.

Question 3

In Planck's model of blackbody radiation, the quantity that does not have discrete values is the

A) atomic vibrational frequency.
B) atomic vibrational wavelength.
C) atomic vibrational amplitude.
D) All of the above quantities have discrete values.

Answer 3

All of the above quantities have discrete values.

Question 4

The color in the visible spectrum associated with the lowest temperature is

A) yellow.
B) red.
C) blue.
D) white.
E) green.

Question 5

Wien's Law relates the

A) maximum wavelength emitted by a blackbody to the absolute temperature of the body.
B) minimum wavelength emitted by a blackbody to the absolute temperature of the body.
C) wavelength where the energy emitted by a blackbody is a maximum to the absolute temperature of the body.
D) wavelength where the energy emitted by a blackbody is a minimum to the absolute temperature of the body.
E) None of the above is correct.

Question 6

The radiation of a reference blackbody peaks at a frequency of $500 \times 10 ^ { 15 }$ Hz. If a second blackbody has a peak radiation at half that frequency, its temperature is (compared to that of the reference body)

A) half as great.
B) twice as great.
C) exactly equal because they are both blackbodies.
D) More information is needed to work out the answer.

Question 7

A blackbody is not

A) a good heat absorber.
B) a good heat radiator.
C) a good heat reflector.
D) All of the above are correct.

Question 8

The spectral emittance is defined as the

A) energy per volume emitted by a glowing body per unit wavelength.
B) power emitted by a glowing body per unit frequency.
C) energy per unit time per unit area emitted by a glowing body per unit wavelength.
D) power emitted by a glowing body per unit frequency per unit area.
E) None of the above is correct.

Question 9

The temperature of your body is 35^oC. The peak wavelength of the radiation it emits is

A) 9.4 $\mu$ m.
B) 9.4 mm.
C) 35 mm.
D) 83 $\mu$ m.
E) 83 mm.

Question 10

The wavelength corresponding to the most intense light emitted by a giant star of surface temperature 9000 K is

A) 572 nm.
B) 322 nm.
C) 311 nm.
D) 261 nm.
E) None of the above is correct.

Question 11

An ear thermometer measures the patient's temperature by detecting

A) the intensity of infrared radiation leaving the eardrum.
B) the frequency of infrared radiation leaving the eardrum.
C) accelerated charged particles near the surface of the eardrum.
D) accelerated neutral particles near the surface of the eardrum.
E) None of the above is correct.

Question 12

The temperature of your body is 35^oC. An estimate of the power emitted by your body (assumed blackbody) is

A) 10²⁰ W.
B) 10⁹ W.
C) 10³ W.
D) 10^-5 W.
E) 10^-9 W.

Question 13

When temperature increases, the amount of radiation emitted

A) increases.
B) decreases.
C) stays the same.
D) More information is needed to work out the answer.

Question 14

The amount of radiation emitted is

A) the slope of the tangent to the wavelength versus intensity graph.
B) the product between the wavelength and its corresponding intensity.
C) the area under the intensity versus wavelength graph.
D) the area under the wavelength versus intensity graph.
E) None of the above is correct.

Question 15

An electron is accelerated by a potential difference of 20 V. The change in the electron's kinetic energy is

A) 0.810 *10^-19 J.
B) 1.62 *10^-19 J.
C) 3.24 * 10^-19 J.
D) 4.86 * 10^-19 J.
E) None of the above is correct.

Question 16

According to classical physics, if electromagnetic radiation were to strike an electrode, the consequence that would be puzzling is that

A) the number of electrons ejected would be proportional to the brightness of the radiation.
B) the kinetic energy of the electrons ejected would be proportional to the brightness of the radiation.
C) no electrons would be ejected if the light (electromagnetic radiation) were too dim.
D) no electrons would be ejected if the wavelength of the light were too long.

Question 17

The kinetic energy of a photoelectron depends on the

A) wavelength of light.
B) intensity of light.
C) duration of illumination.
D) angle of illumination.
E) all of the above.

Question 18

Ultraviolet light shining on an initially uncharged electroscope has no noticeable effect on the electroscope because

A) the wavelength of the ultraviolet light is too large to extract the electrons bound in the metal.
B) the frequency of the ultraviolet light is too large to extract the electrons bound in the metal.
C) the speed of the emitted photoelectrons is too large.
D) the speed of the emitted protons is too large.
E) None of the above is true.

Question 19

The "stopping potential" associated with the photoelectric effect is the electric potential necessary to stop

A) electrons from leaving the metal illuminated.
B) photons from leaving the metal illuminated.
C) electrons from reaching the collecting electrode.
D) photons from reaching the collecting electrode.
E) the photoelectric effect.

Question 20

The photoelectric effect exhibits a threshold effect that can be stated as follows:

A) There is a minimum incident radiation frequency to eject electrons from a metal.
B) There is a minimum incident photon energy to eject electrons from a metal.
C) Electrons in a metal are attracted by a force that must be counteracted for ejection to occur.
D) All of the above are correct.
E) None of the above is correct.

Question 21

Classically, when electromagnetic radiation strikes an electron, we expect that

A) the electron will oscillate at the same frequency as that of the incident radiation.
B) the electron will radiate at the same frequency as that of the incident radiation.
C) the perceived frequency of the electron radiation will be unchanged when it travels at right angles to the original direction of the incident radiation.
D) All of the above are correct.
E) None of the above is correct.

Question 22

The photoelectric effect is explainable assuming

A) that light is a wave.
B) that light is a particle.
C) that light has a wave-particle dual character in classical theory.
D) The photoelectric effect cannot be explained with classical theory.
E) None of the above is correct.

Question 23

A photon is a particle that

A) needs a medium to travel in.
B) has a velocity that varies with the photon frequency.
C) has zero electric charge.
D) has zero electric field associated with it.
E) None of the above is correct.

Question 24

The intensity of a beam of light is increased, but the light's frequency is unchanged. As a result,

A) the photons travel faster.
B) the photons travel slower.
C) the photons are larger.
D) the photons have more energy.
E) None of the above answers is correct.

Question 25

Photon A has half the energy of photon B. The momentum of A is

A) four times the momentum of B.
B) twice the momentum of B.
C) the same as the momentum of B.
D) half the momentum of B.
E) one-quarter the momentum of B.

Question 26

Photon A has twice the energy of photon B. That means that photon A has a higher

A) speed than photon B.
B) wavelength than photon B.
C) mass than photon B.
D) charge than photon B.
E) frequency than photon B.

Question 27

The energy carried by a photon of wavelength 550 nm is

A) 5.50 *10^-9 J.
B) 3.44* 10^-9 J.
C) 3.61*10^-19 J.
D) 8.80 * 10^-19 J.
E) None of the above is correct.

Question 28

A surface is illuminated by light and emits photoelectrons. The intercept (value corresponding to the place where the curve intersects the y axis) of the graph of the maximum kinetic energy of the ejected photoelectrons as a function of the frequency of the incident light is

A) the photoelectric current.
B) the work function.
C) the stopping potential.
D) the cutoff frequency.
E) Plank's constant.

Question 29

A metal has a work function of 4.2 eV. The cutoff wavelength for the metal is

A) 200 nm.
B) 295 nm.
C) 420 nm.
D) 714 nm.
E) None of the above is correct.

Question 30

A metal having a work function of 4.2 eV is illuminated by light of 200-nm wavelength. The maximum kinetic energy of the photoelectrons is

A) 2.0 eV.
B) 2.1 eV.
C) 4.2 eV.
D) 8.4 eV.
E) none of the above.

Question 31

A surface is illuminated by light and emits photoelectrons. If the frequency of the light is doubled, the kinetic energy of the ejected photoelectrons

A) increases by a factor less than 2.
B) increases by a factor more than 2.
C) stays the same.
D) decreases by a factor less than 2.
E) decreases by a factor more than 2.

Question 32

Two surfaces, A and B, are illuminated by light of the same wavelength. Both surfaces emit photoelectrons. If the stopping potentials are $\phi$ and 2 $\phi$ , respectively, their kinetic energies are related by

A) K_A - K_B = $\phi$
B) K_B - K_A = $\phi$
C) K_A + K_B = $\phi$
D) K_A + K_B = 3 $\phi$
E) None of the above is correct.

Question 33

When light of wavelength 250 nm is incident on a metal surface, the stopping potential of the photoelectrons is 1.00 eV. The threshold frequency for the metal surface is

A) 14.4 *10¹⁴ Hz.
B) 12.0 * 10¹⁴ Hz.
C) 9.59 * 10¹⁴ Hz.
D) 2.41 * 10¹⁴ Hz.
E) None of the above is correct.

Question 34

A 1.0-V stopping potential is required to make the photocurrent zero when a monochromatic light is incident on the surface of a metal with work function 3.40 eV. The wavelength of light is

A) 248 nm.
B) 365 nm.
C) 544 nm.
D) 775 nm.
E) None of the above is correct.

Question 35

An isolated aluminum (work function 4.08 eV) sphere of radius 7.00 cm, initially uncharged, is illuminated by ultraviolet light of wavelength 200 nm. The charge induced on the sphere is

A) 3.85 *10¹¹ C.
B) 3.85 *10^-11 C.
C) 7.05* 10^-19 C.
D) 1.66 * 10^-11 C.
E) 1.66* 10¹¹ C.

Question 36

The Compton wavelength is the wavelength of

A) an electron.
B) a photon.
C) a proton.
D) a photoelectron.
E) None of the above is correct.

Question 37

A beam of X-rays of frequency f is incident upon a material that scatters the beam in various directions. The frequency of the scattered X-rays is

A) larger than f.
B) less than f.
C) exactly f.
D) either larger or less than f, but never equal to f.
E) None of the above is correct.

Question 38

X-rays of wavelength 0.400000 nm are scattered from a material. The wavelength of the X-rays scattered at an angle of 45^o to the incident beam is

A) 0.200000 nm.
B) 0.282843 nm.
C) 0.400000 nm.
D) 0.400710 nm.
E) None of the above is correct.

Question 39

When the accelerating voltage in an X-ray tube is doubled, the minimum wavelength of the X-rays

A) is increased to four times the original value.
B) is increased to twice the original value.
C) stays the same.
D) is decreased to half the original value.
E) is decreased to one-fourth the original value.

Question 40

If the scattering angle in a Compton scattering is 90^o, the corresponding wavelength shift is

A) 2.43 * 10^-12 m.
B) 2.43 * 10^-9 m.
C) 3.42 * 10^-9 m.
D) 3.42 *10^-12 m.
E) 0 m.

Question 41

In the Compton effect, as the scattering angle increases, the frequency of the X-rays scattered at that angle

A) increases.
B) stays the same.
C) decreases.
D) either increases or decreases.

Question 42

A 0.001215-nm photon scatters from a free electron. The photon scattering angle for which the electron recoiling energy is the same as the energy of the scattered photon is

A) 30^o.
B) 60^o.
C) 90^o.
D) 120^o.
E) 180^o.

Question 43

A 0.100-nm photon collides with a stationary electron. After the collision, the photon recoils backward and the electron moves forward. The electron's kinetic energy is

A) 800 keV.
B) 592 keV.
C) 400 keV.
D) 243 keV.
E) 104 keV.

Question 44

A 0.100-nm photon collides with a stationary electron. After the collision, the photon recoils backward and the electron moves forward. The electron's momentum is

A) 12.4 keV/c.
B) 21.8 keV/c.
C) 49.6 keV/c.
D) 74.4 keV/c.
E) 88.7 keV/c.

Question 45

X-rays of wavelength 0.350 nm are incident on a material. Scattered X-rays are observed at an angle of 60^o to the incident beam. The fraction of energy lost by the photon is

A) 1.66* 10^-3.
B) 3.45 * 10^-3.
C) 6.92 *10^-3.
D) 7.02 * 10^-2.
E) 9.56 * 10^-2.

Question 46

The reason the wavelike nature of a moving football is not noticed in everyday life is that

A) its energy is too small.
B) its frequency is too small.
C) its wavelength is too small.
D) All of the above are correct.
E) None of the above is correct.

Question 47

The Heisenberg uncertainty relations restrict the precision of simultaneous knowledge of the x component of a photon's position and its

A) x component of momentum.
B) y component of momentum.
C) z component of momentum.
D) All of the previous responses are correct.
E) None of the previous responses is correct.

Question 48

The Heisenberg uncertainty relations imply that if we know the x component of a particle's position within some specified precision, then we

A) must know the x component of its momentum to at least some corresponding precision.
B) are capable of knowing the x component of its momentum to at most some corresponding precision.
C) can calculate the x component of its momentum precisely.
D) All of the previous responses are correct.
E) None of the previous responses is correct.

Question 49

If the wavelength of a photon is known very precisely, then so is each of the following except its

A) energy.
B) momentum.
C) frequency.
D) location.