Physics 202 MWF 10:20 Spring 1996 (Ford)
Exam III Chapts. 31-34 in SZY College Physics 7e
Show all your work. Partial credit will be given if earned. Write your
answers in the blanks provided.
(16 pts) 1. Two long, straight, parallel wires are 0.60 m apart. The lower
wire (wire #1) has a current I1 = 4.0 A that is in the
direction from left to right, as shown in the sketch. Point P
is 0.40 m above wire #1.
a) What are the magnitude and direction of the magnetic field
B1 at point
P due to wire #1? (Show the direction of B1 in the sketch.)
Ans. B1 = ________________
direction ______________
b) What must be the magnitude and direction of the current I2
in wire
#2 for the resultant field at point P due to both wires to be zero?
Ans. I2 = _________________
direction (also show on sketch) ______________
(18 pts) 2. Consider the circuit sketched below:
a) Switch S1 is closed with S2 kept
open. Just after S1
is closed what is
i) the potential vac across the resistor?
Ans. ___________________
ii) the rate
i/t
at which the current through the resistor is increasing?
Ans. _________________
b) After switch S1 has been closed for a long time,
S2 is closed
and S1
is opened. Just after S2 is closed what is
i) the potential vac across the resistor?
Ans.________________
ii) the magnitude
|i/t|
of the rate at which the current through the resistor is decreasing?
Ans. _____________
(16 pts) 3. An L-C circuit consists of an inductor with
L =0.800 H and a
capacitor with C = 6.00 × 10-4 F. The initial
charge on the capacitor is
5.00 µC and the initial current in the inductor is zero.
a) During the current oscillations, what is the maximum energy stored in the
inductor?
Ans. _________________
b) When the charge on the capacitor is 3.00 µC, what is the energy
stored in the inductor?
Ans. _____________
(14 pts) 4. Determine the direction of the current induced in circuit II
in each of the following situations. (State whether the induced current passes
through the resistor R2 in the direction
a to b or
the direction b to a.)
a) Switch S is closed.
Ans. ________________
b) With switch S remaining closed, coil II is moved
farther away from coil I.
Ans. ___________________
(18 pts) 5. In the sketch below the rod ab makes contact with metal rails
that are 0.50 m apart. The resistance of the rail plus rod circuit is
5.0 
and may be considered to be constant. There is a uniform magnetic field with
magnitude B = 2.0 T and direction out of the plane of the paper. The
rod is
pulled to the left at a constant speed of v = 0.40 m/s.
a) Is the induced current in the circuit clockwise or counterclockwise?
(Show the direction of the induced current on the sketch.)
Ans. __________________
b) What is the magnitude of the induced current?
Ans. __________________
c) What external force Fext is required to move the rod at
constant speed?
Ans. _______________
(18 pts) 6. In an L-R-C series circuit
R = 600 ,
L = 0.200 H,
and C = 8.00 × 10-8 F. The voltage amplitude of the
source is
V = 120 V. The source is operated at the resonant angular frequency
of the
circuit.
a) What is the current amplitude?
Ans. __________________
b) What is the voltage amplitude VR of the voltage
across the resistor?
Ans. _______________
c) What is the voltage amplitude VL of the voltage
across the inductor?
Ans. ____________________
d) What is the phase angle ø of the source voltage
with respect to the current?
Ans. ______________