The windings of an electromagnet have inductance L = 8.0 H and resistance R = 2.0 Ω. A 100.0-V dc power supply is connected to the windings by closing switch S2.

(a) What is the current in the windings?
(b) The electromagnet is to be shut off. Before disconnecting the power supply by opening switch S2, a shunt resistor with resistance 20.0 Ω is connected in parallel across the windings. Why is the shunt resistor needed? Why must it be connected before the power supply is disconnected?
(c) What is the maximum power dissipated in the shunt resistor? The shunt resistor must be chosen so that it can handle at least this much power without damage.
(d) When the power supply is disconnected by opening switch S2, how long does it take for the current in the windings to drop to 0.10 A?
(e) Would a larger shunt resistor dissipate the energy stored in the electromagnet faster? Explain.

Transcribed Image Text:

Electromagnet Shunt S resistor S2 de power supply