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Unformatted text preview: solenoid, is
10m. The inductance of the solenoid is L=100mH. The resistivity of Cu is 1.68x10-8 Ωm.
The battery has the polarity shown and no internal resistance. There is a small square
loop of wire next to the long wire in the circuit. Assume the small square loop has
negligible self-inductance and neglect any effect of the small loop on the circuit.
At time t=0 the switch S is closed. 1second after S is closed, the current in the small
square loop is measured to be 1µ A.
(a) Does the current in the small loop flow clockwise or counterclockwise? Explain.
(b) Find (in µA) (i) the current in the small square loop 2 seconds after the switch S is
closed, and (ii) immediately after the switch S is closed. Explain all steps and show all
intermediate results clearly.
2 -Q(t) a
1 ! The capacitor in the figure has round plates of radius a=10cm. The charge in the capacitor
plates is changing with time according to the equation
# t &m
Q( t ) = Q0 % ( with Q0=1C, τ=1ms, and the exponent m=2. There are two small wire
loops in the gap between the capacitor plates, labeled 1 and 2 in the figure. They are both
in the plane of the paper, loop 1 is centered right on the line that goes through the center
of the capacitor plates, and loop 2 is vertically above it at distance 10cm, i.e. right at the
edge of the capacitor plates. They have resistance R1=5Ω and R2=10Ω respectively, and
both have area 1cm2. At time t=1s:
(a) Will there be current flowing in loop 1? In loop 2? Explain why qualitatively, without
doing any calculation.
(b) Calculate the currents flowing in loop 1 and loop 2, in µA, if any, at time t=1s. Show
all steps in the calculation, name all laws that you use, and show all intermediate results.
(c) Assume the exponent in the equation for Q(t) is m=1 instead of m=2, and answer
question (a) above again....
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This document was uploaded on 02/26/2014 for the course PHYS 4c at UCSD.
- Fall '08