1. 21.1 Electromagnetic induction Electromagnetic induction III Practical 21.3 Purpose To produce an electric current by changing the magnetic field through a coil. Procedure 1. Connect coil A to a battery via a switch and a rheostat. 2. Connect coil B to a galvanometer. coil B galvanometer coil A battery rheostat switch Video: Practical 21.3 Simulation: Electromagnetic induction III

2. 21.1 Electromagnetic induction 3. Place the two coils side by side as shown. 4. Observe the deflection of the galvanometer (a) at the moment when you close the switch (b) when the switch is kept closed (c) at the moment when you open the switch. coil B galvanometer coil A battery rheostat switch

3. 21.1 Electromagnetic induction 5. Close the switch again. 6. Reduce the current flowing through coil A by increasing the resistance of the rheostat quickly. 7. Keep the current unchanged for a few seconds. 8. Increase the current back to its original value. 9. Observe the deflection of the galvanometer in each step.

4. 21.1 Electromagnetic induction Under what conditions would the galvanometer deflect? Discussion (1) At the moment when the switch is closed or opened (2) The current through the coil changes