March 24, 2000 Physics 208
Exam 2
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: _________
b. What is the force on an electron (q = -1.6 x 10^{-19}
C) 15 mm from the axis of the wire moving parallel to the current with
a speed of 3 x 10^{6} m/s? (8 pts.)
c. A second, long straight wire is parallel to the first with its axis
a distance of 15 mm from the other’s axis and carries a current of 10 A
in the opposite direction. What is the force on a unit length (1 m) of
this wire? (8 pts.)
First Name: ___________________ Last Name: ____________________ Section: _________
b. Assume the length of the loop is changing at a rate of dx/dt
= 4 cm/s. What is the emf induced in the loop? (8 pts.)
c. If the loop has a resistance of 0.5
?, what force is required to expand the loop at a rate of dx/dt
= 4 cm/s? (9 pts.)
First Name: ___________________ Last Name: ____________________ Section:
_________
a. What is the magnitude of the potential difference across the inductor
at 6 ?s after the switch is closed? (9
pts.)
b. What is the current I at 6 ?s
after the switch is closed? (9 pts.)
c. What is the current I after the switch has been closed for
a long time? (7 pts.)
First Name: ___________________ Last Name: ____________________ Section:
_________
b. At the frequency calculated above, what is the peak voltage across
the inductor? (9 pts.)
c. At the frequency calculated above, what wavelength electromagnetic
wave is emitted by the circuit? (8 pts.)