Physics 202 MWF 10:20 Spring 1999 (Ford)
Exam IV Chapts. 26(sects 9--13), 27, 29 in Cutnell and Johnson 4e


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


(17 pts) 1. A plastic film with index of refraction 2.5 is put on the surface of a car window to increase the reflectivity and keep the interior of the car cooler. The window glass has index of refraction 1.6. What minimum thickness (not counting zero thickness) of the plastic film is required if light of wavelength (measured in air) 400 nm reflected from the two sides of the film is to interfere constructively?

Ans. ____________


(14 pts) 2.
a) A farsighted eye has a near point of 250 cm. What is the focal length of the lens, placed very close to the eye, that will correct the vision so that the eye can clearly view objects that are a distance of 25 cm from the eye? Is the lens converging (positive f) or diverging (negative f)?

Ans. f = ____________

converging or diverging? _______________

b) A nearsighted eye has a far point of 300 cm. What is the focal length of the lens, placed very close to the eye, that will correct the vision so that the eye can clearly view objects that are a large distance from the eye? Is the lens converging (positive f) or diverging (negative f)?

Ans. f = ________________

converging or diverging?______________


(17 pts) 3. When ultraviolet light with a wavelength of 200 nm falls on a certain metal surface the maximum kinetic energy of the emitted photoelectrons is 1.8 eV. What is the longest wavelength of light that will produce photoelectrons from this surface?

Ans. ____________________


(16 pts) 4. In Young's double-slit experiment, coherent light of wavelength 400 nm produces a second order bright fringe at a certain location on a flat screen that is a distance L from the slits.

a) What wavelength of visible light (380 to 750 nm) would produce a dark fringe at this same location on the screen?

Ans. _______________

b) If electrons are used instead of photons, what must the kinetic energy of the electrons be to produce a second-order interference maximum at this same location on the screen? Express your answer in eV.

Ans. _______________


(16 pts) 5. An incident X-ray photon is scattered from an electron that is initially at rest. The photon is scattered straight back at an angle of 180° from its initial direction. The wavelength of the scattered photon is 0.0830 nm.

a) What is the wavelength of the incident photon?

Ans. ________________

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

Ans. ________________

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

Ans. __________________


20 pts) 6. An object 2.0 mm tall is placed 15 cm to the left of a converging lens which is in turn 26 cm to the left of a diverging lens. The converging lens has f₁ = +10 cm and the diverging lens has f₂ = -10 cm.

a) How far is the final image from the object?

Ans. _______________

b) Is the final image real or virtual?

Ans. _______________

c) Is the final image upright or inverted?

Ans._______________

d) What is the height of the final image?

Ans. ______________