Physics 202 MWF 10:20 Spring 1994 (Ford)
Exam IV Chapts. 37,38,39,41 in SZY College Physics 7th ed.


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


(18 pts) 1. When light of wavelength = 200 nm shines on a metal surface, the maximum kinetic energy of the photoelectrons produced is 4.0 eV.

a) What is the work function (in electronvolts) for the metal surface?

Ans. __2.20 eV__

b) What is the maximum wavelength the light can have and still produce photoelectrons for this surface?

Ans. __564 nm__


(18 pts) 2. A layer of water (n = 1.33) 4.0 cm deep floats on a layer of glycerine (n = 1.47) that is 6.0 cm deep. A dime rests at the bottom of the glycerine. What is the apparent depth of the dime beneath the top surface of the water when it is viewed at normal incidence? (That is, what is the distance from the top surface of the water to the final image of the dime?)

Ans. __7.09 cm__


(18 pts) 3. A converging lens with a focal length of 6.0 cm forms an image of a 5.00 cm tall object that is to the left of the lens. The image is 40.0 cm tall and erect.

a) How far is the object from the lens?

Ans. __5.25 cm__

b) How far is the image from the lens?

Ans. __42 cm__

c) Is the image real or virtual?

Ans. __virtual__


(16 pts) 4. Two radio antennas A and B radiate in phase. Antenna B is 110 m to the right of antenna A. Consider point Q along the extension of the line connecting the antennas, a distance of 55 m to the right of antenna B. The antennas radiate waves of the same frequency, and this frequency can be varied. What is the smallest frequency for which there will be destructive interference at point Q?

Ans. __1.36 × 10⁶ Hz__


(12 pts) 5. An atom emits a photon when it undergoes a transition from a state with energy -2.0 eV to a state with energy -7.0 eV. What is the frequency of the photon that is emitted?

Ans. __1.21 × 10¹⁵ Hz__


(18 pts) 6. An object is 8.00 m from a wall. You want to use a concave mirror to project a real image of the object on the wall, with the height of the image three times the height of the object.

a) Is the image erect or inverted?

Ans. __inverted_

b) How far is should the mirror vertex be from the object?

Ans. __4 m__

c) What must be the radius of curvature of the mirror?

Ans. __6 m__