1) A 25.0-mH inductor is connected in series to a 20.0-? resistor through a 15.0

Question

1) A 25.0-mH inductor is connected in series to a 20.0-? resistor through a 15.0-V dc power supply and a switch. If the switch is closed at t = 0 s, what is the time constant of this circuit?

2)The wire in the figure carries a current I that is increasing with time at a constant rate. The induced emf in each of the loops is such that

3) If the rate of change of the magnetic field applied to a loop of wire is doubled, what happens to the induced emf in that loop assuming all the other parameters remain unchanged?

4) A rectangular coil lies flat on a horizontal surface. A bar magnet is held above the center of the coil with its north pole pointing down. What is the direction of the induced current in the coil?

Explanation / Answer

1)time constant = L/R = 25x10^-3/20 = 1.25 milli seconds

2)induced emf in B=0

In C,the current direction is in counter clockwise direction and in A it is in clockwise direction.

EMF induced is in the same direction as the current

U can use right hand screw rule to obtain the above result.The directions should be such that,the field due to the induced current opposes the field due to the current carrying wire.(Since it is increasing).

3)e= -Nd(flux)/dt = -NAdB/dt

so if dB/dt doubles induced emf doubles

4)As the magnet is held stationary,the flux passing through the rectangular loop is constant,hence there is no induced EMF

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