Physics 202 MWF 10:20 Spring 2002 (Ford)

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


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


(3 pts) 1. In a photoelectric effect experiment, electrons with maximum kinetic energy KE_max are produced when light of wavelength and intensity S is used. If the intensity of the light is doubled ( stays the same), what happens to KE_max of the photoelectrons that are produced?

(a) increases
(b) decreases
(c) stays the same <-------


(3 pts) 2. A photon of frequency f undergoes Compton scattering from an electron at rest and scatters through an angle of 180°. The frequency of the scattered photon is f '. Which statement is true:

(a) f = f '
(b) f ' is less than f <------
(c) f ' is greater than f

(3 pts) 3. A photon with energy E₁ has momentum p₁. If the energy of the photon is doubled (E₂ = 2 E₁), what is then the momentum p₂ of the photon?

(a) p₂ = p₁
(b) p₂ = (2)^1/2p₁
(c) p₂ = 2p₁ <------
(d) p₂ = p₁/(2)^1/2
(e) p₂ = p₁/2


(3 pts) 4. Coherent light with wavelength passes through a single slit that has width W and the diffraction pattern is observed on a screen a distance L from the slit. If the slit is made more narrow (W is decreased), what happens to the width of the central diffraction maximum as measured on the screen?

(a) it stays the same
(b) it increases <------
(c) it decreases


(3 pts) 5. Two coherent sources, A and B, emit identical waves that have wavelength 1.50 m. Point P is 4.50 m from A and 7.50 m from B. Is the interference at P constructive or destructive?

(a) constructive <------
(b) destructive


(3 pts) 6. The resolving power of a camera is a measure of its ability to distinguish two closely spaced objects. If diffraction is the only factor affecting the resolving power, does the resolving power of the camera increase or decrease when the diameter of the lens is increased?

(a) increase <------
(b) decrease


(3 pts) 7. A hydrogen atom (Z = 1) is in a state with energy -1.51 eV. In the Bohr model, what is the orbital angular momentum of the electron in the atom

(a) 0.5 (h/2)
(b) h/2
(c) 2(h/2)
(d) 3(h/2) <------
(e) 4(h/2)
(f) 9(h/2)


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


(12 pts) 8. An atom is in a state with energy -12.0 eV. It absorbs a photon of wavelength 500 nm. What is the energy of the atom after it absorbs the photon?

Ans. ____- 9.5 eV___


(16 pts) 9.
A photon has wavelength 200 nm.

a) What is the momentum of the photon?

Ans. ___3.32 × 10^-27 kg·m/s____

b) What is the energy of the photon, in eV?

Ans. ____6.22 eV_______

An electron has de Broglie wavelength 200 nm.

c) What is the momentum of the electron?

Ans. ____3.32 × 10^-27 kg·m/s____

d) What is the energy of the electron, in eV?

Ans. ____3.78 × 10^-5 eV___

(17 pts) 10. Light of wavelength 400 nm produces photoelectrons with a maximum kinetic energy of 1.6 eV when it falls on a certain metal surface. What is the maximum wavelength of light that will produce photoelectrons from this surface?

Ans. ___825 nm___


(16 pts) 11. Coherent light with wavelength 400 nm passes through two very narrow slits that are separated by 0.20 mm and the resulting interference pattern is observed on a screen that is 4.0 m from the slits. What is the width (in meters) of the central interference maximum?

Ans. ___8 × 10^-3 m__


(18 pts) 12. Light of wavelength 400 nm falls perpendicularly on a thin film of gasoline (n = 1.40) that is floating on water (n = 1.33). What is the minimum nonzero thickness of the film for which there is constructive interference in the reflected light?

Ans. ____71.4 nm___