Electromagnetic Induction

Question 1

State Faraday’s Law of Electromagnetic Induction

Answer 1

Faraday’s Law states that the magnitude of the induced e.m.f. is proportional to the rate of change of the magnetic lines of force linked with the circuit or the rate at which the lines of force are cut.

Question 2

State Lenz’s Law of Electromagnetic Induction

Answer 2

Lenz’s Law states that the direction of the induced current is such that its magnetic effect always opposes the change producing it.

Question 3

State 4 ways to increase the e.m.f./current induced in an A.C. Generator

Answer 3

1. Increase the speed of rotation.
2. Increase the number of turns in the coil.
3. Increase the magnetic field strength using stronger magnets.
4. Winding the coil on a soft iron core to concentrate the magnetic field lines through the coil.

Question 4

What is the formula for turns ratio?

Answer 4

turns ratio: Ns/Np = Vs/Vp = Ip/Is

Ns: Number of turns at the secondary coil
Np: Number of turns at the primary coil
Vs: Voltage at the secondary coil
Vp: Voltage at the primary coil
Is: Current at the secondary coil
Ip: Current at the primary coil

Question 5

What is the formula for an ideal transformer?

Answer 5

Power input = Power output
Pp=Ps
IpVp=IsVs

Question 6

4 ways to increase transformer efficiency.

Answer 6

1. Use a soft iron core to concentrate magnetic field lines.
2. Use low-resistance copper wires to reduce energy loss in the form of heat.
3. Use a laminated soft iron core to reduce heat loss due to eddy currents.
4. Use a special core design to ensure maximum linkage of magnetic field lines from primary to secondary coils.

Question 7

Transmission of Power Formula

Answer 7

Ploss=I²R

Where I = transmission current, R = resistance in cable

Question 8

3 uses of C.R.O.

Answer 8

1. Measuring d.c. and a.c. voltages
2. Displaying waveforms
3. Measuring time and frequency

Question 9

Waveforms of d.c. supply

Answer 9

Off: a single dot on the centre point
On: A horizontal straight line

Question 10

Waveforms of a.c. supply

Answer 10

Off: A vertical straight line at the centre
On: A wave