Physics 202 MWF 10:20 Spring 2000 (Ford)

Exam IV Chapts. 27, 29, 30 in Cutnell and Johnson 4e


Note:
c = 3.00 × 10⁸ m/s
h = 6.63 × 10^-34 J·s
electron mass m = 9.11 × 10^-31 kg
electron charge e = 1.60 × 10^-19 C
1 eV = 1.60 × 10^-19 J


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


(4 pts) 1. The distance between the m = 1 and m = 2 bright fringes in a two-slit interference pattern is 0.12 mm. The screen is a very large distance from the slits so the angular position of these fringes is very small. If the entire apparatus (source, slits, screen) is immersed in water (n = 1.33), what then is the distance between these two fringes?

a) 0.06 mm
b) 0.09 mm
c) 0.12 mm
d) 0.16 mm
e) 0.24 mm


(3 pts) 2. You use a lens of diameter d and light of wavelength and frequency f to form an image of two closely spaced and distant objects. To increase the resolving power you should:

a) use a lens with a smaller diameter
b) use light of larger frequency
c) use light of larger wavelength
d) use a lens with a larger focal length


(3 pts) 3. In a photoelectric effect experiment which of the following will increase the maximum kinetic energy of the photoelectrons:

a) use light of greater intensity
b) use light of greater frequency
c) use light of greater wavelength
d) use a metal surface with a larger work function


(3 pts) 4. A stone is dropped from the top of a building. Neglect the effects of air resistance. As the stone falls, its de Broglie wavelength

a) increases
b) decreases
c) remains the same


5. A hydrogen atom is in its ground state. In the Bohr model the radius of the electron orbit in this state is 5.29 × 10^-11 m.

(3 pts) In the Bohr model the de Broglie wavelength of the electron in this state is

a) 5.29 × 10^-11 m
b) 3.32 × 10^-10 m
c) 1.66 × 10^-10 m
d) 1.68 × 10^-11 m
e) 8.84 × 10^-12 m

(2 pts) In the Bohr model the angular momentum of the electron in the ground state of the hydrogen atom

a) is 0
b) is h
c) is h/(2)
d) is h/
e) can have several possible values

(2 pts) In the quantum mechanical description of the hydrogen atom the angular momentum of the electron in the ground state of the hydrogen atom

a) is 0
b) is h
c) is h/(2)
d) is h/
e) can have several possible values


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


(14 pts) 6. An atom is in an excited state that has energy -3.0 eV. The atom emits a photon with wavelength 400 nm when it makes a transition to its ground state. What is the energy of the ground state?

Ans. __________________


(16 pts) 7. Coherent light is passed through a single slit whose width is 0.3 mm. The diffraction pattern is observed on a screen 750 mm from the slit and the width of the central maximum is 2.00 mm. If electrons are used instead of light, what must be the velocity v of the electrons if they are to produce a diffraction pattern of the same width, 2.0 mm?



Ans. _____________________


(18 pts) 8. When ultraviolet light with a wavelength of 400 nm falls on a certain metal surface the maximum kinetic energy of the emitted photoelectrons is 1.1 eV. What is the maximum kinetic energy of the photoelectrons when light of wavelength 300 nm is used?

Ans. ___________________


(16 pts) 9. An incident X-ray photon of wavelength 0.0900 nm is scattered in the backward direction ( = 180°) from an electron that is initially at rest.

a) What is the momentum of the scattered photon?

Ans. ___________________

b) What is the kinetic energy of the electron after the collision?

Ans. ___________________


(16 pts) 10. Coherent light with wavelength = 500 nm in air is incident on a soap film (n = 1.33). There is air on both sides of the film. What is the smallest thickness of the soap film (not counting zero thickness) for which there will be constructive interference between the light reflected at the top and bottom surfaces of the film?



Ans._________________