electromagnetic induction 📽

Question 1

factors affecting magnitude of induced current

Answer 1

1) number of turns of coil
2) strength of magnet
3) speed at which magnet is moved in relation to the solenoid

Question 2

define electromagnetic induction

Answer 2

electromagnetic induction is the process through which an induced emf is produced in a conductor due to a changing magnetic field

Question 3

state Faraday’s law

Answer 3

the magnitude of an induced emf in a circuit is directly proportional to the rate of change of magnetic flux linking the circuit

Question 4

state Lenz’s law

Answer 4

the direction of induced emf and hence induced current, in a closed circuit is always such that its magnetic effect opposes the change in motion producing it

Question 5

explain why a north pole is produced when a north pole is moved towards a solenoid

Answer 5

when north pole of the magnet was moved towards the solenoid, the side nearest the magnet is induced with a North pole. by Lenz’s law, a North pole is induced to oppose the rate of change in magnetic flux linking the magnet and the coil

Question 6

explain how the emf produced by ac generator decreases from horizontal to vertical

Answer 6

when the coil is horizontal, the rate of change of magnetic flux linking the circuit is the greatest, hence induced emf and induced current is at its maximum. as the coil rotates, the rate of change of magnetic flux linking the circuit decreases, hence emf decreases until zero

Question 7

describe the effect of increasing frequency of coil rotation on the emf graph

Answer 7

• increase in rate of change of magnetic flux linking the circuit: increase in amplitude
• increase in frequency: decrease in wavelength

Question 8

explain how a current is induced in the secondary coil of a transformer by an ac current in the primary coil

Answer 8

an alternating current in the primary coil produces a changing magnetic field. the soft iron core links the magnetic field of the primary and secondary coils. there is a rate of change in magnetic flux linkage in the secondary coil, inducing an emf and hence a current

Question 9

transformer formulae

Answer 9

N1 / N2 (turns ratio) = V1 / V2 = I2 / I1

Question 10

why is there a need for transformers in transmitting electricity to homes?

Answer 10

an increase in voltage decreases the current flowing in the wire. this decreases the heating effect of current, minimising power loss

Question 11

why is there a laminated soft iron core?

Answer 11

to reduce the flow of eddy currents, reducing power loss