Physics 202 MWF 10:20 Spring 2001 (Ford)

Exam IV Chapts. 27, 29, 30 in Cutnell and Johnson 5e


Note:
Multiple choice questions. Circle the correct answer. No work need be shown and no partial credit will be given.


(4 pts) 1. Which of the following will increase the maximum kinetic energy of the photoelectrons ejected by light from a metal surface:

(a) increase the intensity of the light
(b) decrease the frequency of the light
(c) decrease the wavelength of the light
(d) use a surface with a larger work function W₀


(3 pts) 2. Coherent radio waves of frequency 6.0 × 10⁸ Hz are emitted from two antennas A and B. Point P is a distance 1.50 m from antenna A and a distance of 1.25 m from antenna B. The interference at point P is

(a) destructive
(b) constructive


(4 pts) 3. Coherent light of wavelength and frequency f passes through a single slit of width W. The diffraction pattern is observed in a screen a distance L from the slit. It is observed that the width of the central maximum is 2.0 mm. Which of the following will decrease the width of the central maximum:

(a) decrease the slit width
(b) decrease the frequency of the light
(c) decreasethe wavelength of the light
(d) increase the distance L of the screen from the slit


(4 pts) 4. The photons for light of wavelength ₁ have momentum p₁ and energy E₁ = 2.0 eV. If the wavelength of the light is changed such that the momentum of each photon is doubled, p₂ = 2p₁, what is the new photon energy E₂?

(a) 0.50 eV
(b) 1.0 eV
(c) 2.0 eV
(d) 4.0 eV
(e) 8.0 eV


(3 pts) 5. In the Bohr model the angular momentum of an electron in the n = 2 first excited energy state of a hydrogen atom

(a) is 0
(b) is 2h
(c) is h/2
(d) is h/
(e) is 3h/2
(f) can have more than one possible value

(3 pts) 6. In the quantum mechanical description of the hydrogen atom the angular momentum of an electron in the n = 2 first excited energy state of a hydrogen atom

(a) is 0
(b) is 2h
(c) is h/2
(d) is h/
(e) is 3h/2
(f) can have more than one possible value



Show all your work. Partial credit will be given if earned. Write your answers in the blanks provided.


(12 pts) 7. Use the Bohr model to calculate the de Broglie wavelength of an electron in the n = 3 energy state of a hydrogen atom.

Ans.___________________


(17 pts) 8. A film of gasoline (n = 1.40) floats on a puddle of water (n = 1.33). There is air above the gasoline. Light that has a wavelength of 500 nm in air falls perpendiuclarly on the film. What is the minimum nonzero thickness of the film for which there will be destructive interference between light reflected at the top and the bottom surface of the film?


Ans._______________


(16 pts) 9. Light of wavelength 200 nm shines on a metal surface and produces the photoelectrons that have a maximum kinetic energy of 1.6 eV. What is the longest wavelength of light that will produce photoelectrons from this surface?

Ans.______________


(17 pts) 10. An incident X-ray photon of wavelength 0.0700 nm is scattered in the backward direction ( = 180°) from an electron that is intiially at rest.

a) What is the energy of the scattered photon?

Ans.____________

b) What is the magnitude of the linear momentum of the electron after the collision?

Ans._________________


(17 pts) 11. Coherent light is passed through two narrow slits whose separation is 4.0 × 10^-5 m. The second-order bright fringe in the interference pattern is located at an angle of 0.03 rad. If electrons are used instead of light, what must be the kinetic energy (in eV) of the electrons if they are to produce an interference pattern for which the second-order maximum is also at 0.03 rad?

Ans.___________________