Electromagnetic induction

Question 1

Electromagnetic induction

Answer 1

Occurs whenever a wire cuts across the lines of a magnetic field. If the wire is part of a complete circuit, the induced emf forces electrons round the circuit.

Question 2

Current at the north pole end of a solenoid

Answer 2

Passes anticlockwise.

Question 3

Current at the south pole end of a solenoid

Answer 3

Passes clockwise.

Question 4

Lenz’s law

Answer 4

The direction of the induced current is always such as to oppose the change that causes the current.

Question 5

Magnetic flux, Φ, equation

Answer 5

Φ = BA

Question 6

Unit of magnetic flux, Φ

Answer 6

Weber (Wb), equal to 1 T m^2

Question 7

Magnetic flux linkage through a coil of N turns

Answer 7

= NΦ = NBA

Question 8

Faraday’s law of electromagnetic induction

Answer 8

The induced emf in a circuit is equal to the rate of change of flux linkage through the circuit.

Question 9

Induced emf equation

Answer 9

ϵ = - N ΔΦ/Δt

Question 10

Root mean sqaure AC value definition

Answer 10

The value of direct current that would give the same heating effect as the AC in the same resistor.

Question 11

I rms

Answer 11

I rms = 1/

Question 12

I rms

Answer 12

I rms = 1/√2 Io

Question 13

V rms

Answer 13

V rms = 1/√2 Vo

Question 14

Transformer rule

Answer 14

Vs/Vp = Ns/Np = Ip/Is

Question 15

Step up transformer

Answer 15

Has more turns on the secondary coil and hence secondary voltage is stepped up from primary voltage.

Question 16

Step down transformer

Answer 16

Has less turns on the secondary coil and hence secondary voltage is stepped down from primary voltage.

Question 17

Efficiency of a transformer equation

Answer 17

IsVs/IpVP x 100%