Experiment 4 (Stored Energy in Inductors. Demonstrates: Inductance, Stored Energy, Faraday’s Law, Lenz’s Law).
Take a small power transformer and identify the primary and secondary leads. Connect the secondary to an LED through a
small resistor as shown in Figure 10.36. Now connect a 1.5 to 6 V battery to the two secondaries by closing the switch S for a
few seconds and then open the switch. The LED will light momentarily. As the current is disconnected, the flux through the
coil of the transformer is reduced from some value to zero in a short time. The result is an induced emf which can be many
times larger than the voltage of the battery. The polarity of this emf is opposite that of the battery and hence the LED lights
up and dissipates the stored energy in the coil.