ELECTROMAGNETIC INDUCTION

ELECTROMAGNETIC INDUCTION
Key notes:
1. Faraday’s law of electromagnetic induction: When the magnetic field linked
with a circuit changes, an e.m.f. is induced. The induced e.m.f. is directly
proportional to the rate of change of magnetic flux.
2. Lenz’s law: The direction of the induced current is such as to oppose the
change that produces it.
3. An a.c. generator uses the principle of electromagnetic induction.
4. A simple a.c. generator consists of a coil of wire attached to a pair of slip rings
rotating between the poles of a magnet.
5. The slip rings enable the same end of the coil to be in contact with the same
carbon brush.
6. The induced e.m.f. in an a.c. generator is alternating between the maximum
positive value and the minimum negative value continuously.
7. The working principle of a transformer: when an A.C. flows in the primary
coil, the magnetic field changes. This change in magnetic field produces an
induced e.m.f. in the secondary coil.
8. If the transformer is 100% efficient, output power = input power.
9. In electric power transmission, transformers are use to step-up the voltage so
that the current in the transmission cables is small; hence reducing the power
loss in the cables.
10. A.C. rather than D.C. is use for electricity transmission down using
transformers. Transformers do not work on D.C.
Formulas:
 TRANSFORMERS
Voltage of secondary coil, V(s) / Voltage of primary coil, V(p) =
No. of turns in secondary coil, N(s) / No. of turns in primary coil, N(p)
= [V(s) / V(p)] = [N(s) / N(P)]
 If the transformer is 100% efficient,
output power = input power
I(s)V(s) = I(p)V(p)