To demonstrate Faraday’s law of electromagnetic induction 2 primary coil
This demonstrates Faraday’s law on two stationary coils with a switch in one and a galvanometer in the other. 1. Set up the experiment as shown in Fig. 28.3. 2. Close the switch and current flows in the primary coil and causes a magnetic field.
3. This induces an emf and hence a current in the secondary coil.
4. When you open the switch, the galvanometer needle moves the other way. This is because as current drops to 0, the changing magnetic field is diminishing.
switch battery FIG. 28.3
secondary coil
galvanometer
To demonstrate Faraday’s law of electromagnetic induction 3 primary coil
This demonstrates Faraday’s law on two coils: one with an a.c. source and the other with a galvanometer. 1. Set up the experiment as shown in Fig. 28.4. 2. Once the switch is closed, the current alternates constantly.
3. Therefore the galvanometer needle is always moving, showing constant magnetic field change. This is due to continuous current direction change in the primary coil.
a.c. supply switch FIG. 28.4
secondary coil
galvanometer
Faraday’s law can be proven with the electromagnetic induction experiments above. Faraday’s law of electromagnetic induction E ∝ Change in Φ
_______________ t
E = induced emf (V), Φ = magnetic flux (Wb), t = time taken (s) This can also be shown as: E ∝
__________ t
Φ2 − Φ1
E = induced emf (V), Φ2 = final magnetic flux (Wb), Φ1 = initial magnetic flux (Wb), t = time taken (s)
