Physics 1310
Quiz 5_ key x
1. Consider a circular loop of wire in a magnetic field as shown in the picture to the
right. The area of the circular loop through which current flows equals 0.40 m2. The
2.5 Tesla magnetic field points into the page and is decreasing in magnitude at the rate
of 5.0 T/s. The current induced in the loop
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a. flows from left to right through the 5.0 resistor and has magnitude equal to 0.20 A
b. flows from left to right through the 5.0 resistor and has magnitude equal to 0.40 A
c. flows from right to left through the 5.0 resistor and has magnitude equal to 0.20 A
d. flows from right to left through the 5.0 resistor and has magnitude equal to 0.40 A
e. is zero. These is no current in the loop.
0.40 m2 * 5.0 T/s = 2.0 volt  I = 2.0 v / 5.0 = 0.40 A
2. As shown to the right, a 40 cm x 20 cm rectangular loop of
wire is being pushed with constant speed into a uniform
magnetic field that points into the page. The constant
magnetic field is perpendicular to the plane of the loop and
goes through the right part of the loop. The magnitude of the
magnetic field equals 2.0 T. The electric resistance of the
loop equals 2.5 ohms. The speed of the loop equals 5.0 m/s.
The induced current in the loop
a. has magnitude equal to 0.80 A and flows in a clockwise direction in the loop.
b. has magnitude equal to 1.6 A and flows in a clockwise direction in the loop.
c. has magnitude equal to 0.80 A and flows in a counter-clockwise direction in the loop.
d. has magnitude equal to 1.6 A and flows in a counter-clockwise direction in the loop.
e. is zero. There is no current in the loop.
5.0 m/s * 0.20 m * 2.0 T = 2.0 volt  I = 2.0 v / 2.5 = 0.80 A
3. The primary and secondary voltages of a transformer equals 120 volts (rms) and 12 volts (rms),
respectively. The current in the primary circuit equals 2.0 A and the transformer is 100% efficient. The
current in the secondary circuit equals
a. 0.20 A
b. 2.0 A
c. 12 A
d. 20 A
e. 120 A
120 volts x 2.0 A = 12 volts x Is  Is = 20 A
4. An electrical generator is composed of a coil of wire with 2000 turns and magnet with a 0.50 T
uniform B-field. The area of the loop equals 4.0x10-4 m2. The rate of rotation of the coil in the B-field
equals 4.8 revolution per second. Calculate the magnitude of the maximum EMF produced.
4.0x10-4 m2 * 0.50 T * 2 4.8 hz =12 volts
5. In the RLC shown to the right the capacitance of the capacitor
equals 0.10 F and the inductance of the inductor equals 10 H.
Calculate fresonance, the resonance frequency of the circuit.
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fresonance = 1/(2sqrt (10-6)) Hz = 159 Hz
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Extra Credit (5points) As shown to the right, a 40 cm x 20
cm rectangular loop of wire is being pushed with constant
speed into a uniform magnetic field that points into the page.
The constant magnetic field is perpendicular to the plane of
the loop and goes through the right part of the loop. The
magnitude of the magnetic field equals 2.0 T. The electric
resistance of the loop equals 2.5 ohms. The speed of the loop
equals 5.0 m/s. Calculate F, the magnitude of the force required to push the loop into the magnetic
field at this speed.
From 2), I = 0.80 A  F = ILB = 0.80 A * 0.20 m * 2.0 T = 0.32 N