Electromagnetic induction

Question 1

Faraday’s Law

Answer 1

The e.m.f induced in a conductor is proportional to the rate of change of magnetic flux linking the coil

Question 2

Lenz’s Law

Answer 2

An induced current always flows in a direction such that it opposes the change producing it

Question 3

To increase e.m.f. of AC generator

Answer 3

1. Increase no. of turns on coil
2. Increase frequency of rotation of coil
3. Use stronger magnets
4. Insert soft iron core in coil

Question 4

Purpose of slip ring in generator

Answer 4

Allows coil to rotate freely and continuously while making contact with the external circuit through the carbon brushes
Lead induced current in and out of coil without causing entanglement to external circuit when coil is being rotated

Question 5

Purpose of carbon brushes

Answer 5

To ensure continuous contact between slip rings and external circuit

Question 6

Why do transformers only work with AC?

Answer 6

Voltage in secondary coil will only be induced if there is changing magnetic flux

Question 7

Step-up transformers

Answer 7

Ns > Np

Question 8

Step-down transformers

Answer 8

Np > Ns

Question 9

P = IV in transformers

Answer 9

In ideal transformers, P remains constant so I decreases when V increases

Question 10

How is electricity transmitted?

Answer 10

High voltage, very low current
In order to retain as much power as possible,
P = I^2R
R cannot be changed, so I is decreased to decrease power loss