AJM:4 /23/ 09 1
Physics 234 Exam #1 Winter 1992
Name
Please work the problems on separate sheets of paper and staple this sheet to the front. Read each
problem carefully. Make sure that your answers are given with a reasonable number of sig figs and that
you have included appropriate units. I can only give partial credit if I can follow your work, so tr y to be
as clear as possible about what you are doing. A few formulas for reference:
o
⌡
⌠ E⋅dA = q
εo , o
⌡
⌠ B⋅dA = 0 , o
⌡
⌠ E⋅ds = – d
dt ⌡
⌠ B⋅dA , o
⌡
⌠ B⋅ds = µo⎣
⎢
⎡
⎦
⎥
⎤
i + εo d
dt ⌡
⌠ E◊dA
S =
E ∞ B
µo , t = $
1. [25 pt s] The 2.0 µF capacitor at right is charged to 50 V after which
the switch is closed. What is the maximum subsequent current in
the circuit?
2. An LRC circuit is driven at an angular frequency of 4000 rad/s. The 50 ohm resistor in the circuit
dissipates an average 80 mW of power. The rms voltage across the inductor is 3.0 V. The current
leads the generator voltage by 30 degrees.
a) [3 pts] What is the power factor?
b) [3 pts] Is the angular resonance frequency
higher or lower than 4000 rad/s? Explain.
c) [19 pts] Fill in a table like that at right. (ωo is
the angular resonance frequency.)
3. A 1.0 MW transmitter acts as an isotropic source for a 6.0
MHz radio wave. At the position shown in the figure at
right the magnetic field is a maximum and has a value of 2.0 x
10-8 T. It propagates in the direction shown.
a) [5 pts] Indicate the direction of the electric field at the
point shown.
b) [20 pts] How far is this point from the transmitter?
4. In the figure at top right, a magnetic field line encircles the
perimeter of the region between the plates of a capacitor. The field
has a magnitude of 1.0 x 10-8 T and the capacitor p lates have a radius
of 20 cm.
C = 2.0 µF
L = 50 mH
switch
I
rms
!
rms
L
C
"
o
B
Direction of
propagation
B
