1. A coil rotates at 60 revolutions per second in a field of 2x10-2 Tesla. If th
ID: 1533794 • Letter: 1
Question
1. A coil rotates at 60 revolutions per second in a field of 2x10-2 Tesla. If the coil has a cross- sectional area of 20 cm2 and has 1000 turns, what is the amplitude of the EMF in the coil?
2. A 50 mH inductor is placed in parallel with a 100 resistor. Ignoring any resistance in the inductor itself, what is the time constant of this RL circuit?
3. How much voltage is there across a 100 mH inductor if the current is changing at 10 mA/s?
(a) remain unchanged at a positive value, (b) remain positive but decrease to zero, (c) change from positive to negative and then decrease to zero, (d) remain at zero.
Explanation / Answer
1.
N = number of turns = 1000
B = magnetic field = 0.02 T
A = area = 20 x 10-4 m2
w = angular speed = 60 rev/sec = 60 x 2 x 3.14 rad/s = 376.8 rad/s
amplitude of induced emf is given as
Eo = NBA w
Eo = 1000 (0.02) (20 x 10-4 ) (376.8)
Eo = 15.1 volts
2)
Time constant is given as
T = L/R = 0.050 /100 = 0.0005 sec
3)
di/dt = rate of change of current = 10 x 10-3 A/s
L = inductance = 100 x 10-3 H
Voltage across inductor is given as
VL = L (di/dt) = (100 x 10-3) (10 x 10-3 ) = 0.001 Volts
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