May 14, 1999 Physics 208
Final Exam
Print your name and section clearly on all nine 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 two 8½ x 11" sheet of notes and no other references.
The exam lasts exactly 2 hours.
(Do not write below)
SCORE:
Problem 1: __________
Problem 2: __________
Problem 3: __________
Problem 4: __________
Problem 5: __________
Problem 6: __________
Problem 7: __________
Problem 8: __________
TOTAL: ___________
b. What is the electric potential (relative to infinity) 12 cm from
the center of the ball? (8 pts.)
c. What is the force on an electron 15 cm from the center of the ball?
(8
pts.)
b. What is the current in the 15-ohm resistor? (15 pts.)
a. What is the magnitude of the magnetic field 5 cm from the wire?
(8
pts.)
b. What is the force on an electron 5 cm from the wire moving in the
direction of the current with kinetic energy of 100 eV? (8 pts.)
c. If the current is turned uniformly to zero in a time of 500 ?S,
what voltage is induced in a single-turn circular loop with an area of
1 cm^{2}, 5 cm from the wire, and axis parallel to the magnetic
field? (9 pts.)
b. At what frequency (in Hz) does the circuit oscillate after the switch
is opened? (5 pts.)
c. What is the maximum instantaneous power dissipated by the resistor?
(5
pts.)
d. What is the maximum voltage across the inductor? (5 pts.)
e. What is the voltage across the capacitor after the switch has been
open for a long time? (5 pts.)
a. What is the rms electric field 50 cm from the bulb? (5 pts.)
b. What is the rms magnetic field 50 cm from the bulb? (5 pts.)
c. What is the radiation pressure on a black surface 50 cm from the
bulb? (5 pts.)
d. What is the energy (in eV) of the photons emitted by the bulb? (5
pts.)
e. How many photons are emitted by the bulb each second? (5 pts.)
a. What diameter telescope is required to just resolve the laser
beams from the earth? (9 pts.)
b. If the telescope lens has a focal length of 140 cm, how far apart
are the images of the lasers? (8 pts.)
c. If these images are magnified by a second converging lens with a
focal length of 2 cm, how far from the second lens must a photographic
plate be placed so that the images of the lasers are 1 mm apart? (8
pts.)
a. What is the kinetic energy of this electron in eV? (6 pts.)
b. What is the relativistic ?-factor
of this electron? (6 pts.)
c. What is the de Broglie wavelength of the electron? (7 pts.)
d. What wavelength photon is required to eject this electron from the
atom? (6 pts.)
b. What is the charge (Z) and atomic mass (A) of the Plutonium
nucleus? (5 pts.)
c. What fraction of the Americium decays in 100 years? (5 pts.)
d. If the mass of Americium is 1 g, what is its radioactivity (in Curies)?
(5
pts.)
e. What other lepton is produced in the above decay process? (5 pts.)