First Name: ___________________ Last Name: ____________________ Section: _________

April 25, 1997 Physics 208

Exam 3

Print your name and section clearly on all five pages. (If you do not know your section number, write your TAs name.) Show all work in the space immediately below each problem. Your final answer must be placed in the box provided. Problems will be graded on reasoning and intermediate steps as well as on the final answer. Be sure to include units wherever necessary, and the direction of vectors. Each problem is worth 25 points. In doing the problems, try to be neat. Check your answers to see that they have the correct dimensions (units) and are the right order of magnitudes. You are allowed one 8½ x 11" sheet of notes and no other references. The exam lasts exactly 50 minutes.

(Do not write below)

SCORE:

Problem 1: __________

Problem 2: __________

Problem 3: __________

Problem 4: __________

TOTAL: ___________

First Name: ___________________ Last Name: ____________________ Section: _________

1. An electromagnetic wave is produced by an electric charge that oscillates sinusoidally with a frequency of 1011 Hz and propagates through a medium with a permittivity of 1.5 x 10-11 F/m.

a. What is the index of refraction of the medium? (5 pts.)

b. What is the speed of the wave in the medium? (5 pts.)

c. What is the wavelength of the wave in the medium? (5 pts.)

d. If the wave intensity in the medium is 200 W/m2, what is the rms electric field? (5 pts.)

e. What is the rms magnetic field for the above intensity? (5 pts.)

First Name: ___________________ Last Name: ____________________ Section: _________

1. A convex spherical mirror with radius of curvature R = 20 cm produces an upright image one-quarter as high as the object.
2.

a. What is the position of the object? (10 pts.)

b. What is the position of the image? (10 pts.)

c. Is the image real or virtual? (5 pts.)

First Name: ___________________ Last Name: ____________________ Section: _________

3. An oil film (n1 = 1.45) with thickness 280 nm floating on water (n2 = 1.33) is illuminated by white light (400  700 nm) at normal incidence.
4.

a. What (free-space) visible wavelength is dominantly reflected? (10 pts.)

b. What (free-space) visible wavelength is dominantly transmitted into the water? (10 pts.)

c. What color is the transmitted light? (5 pts.)

First Name: ___________________ Last Name: ____________________ Section: _________

5. A 50-kg astronaut takes a trip to Sirius, located 8 light years from Earth traveling at a constant speed of 2.4 x 108 m/s.

a. How much time is required for the trip according to an observer on Earth? (5 pts.)

b. How much time is required for the trip according to the astronaut? (5 pts.)

c. What distance (in light years) does the astronaut measure between Earth and Sirius? (5 pts.)

d. What is the kinetic energy of the astronaut? (5 pts.)

e. How much mass would have to be consumed to accelerate the astronaut to her final speed? (5 pts.)