Magnetic Fields

Question 1

Lenz’s Law

Answer 1

Lenz’s law states that the direction of the induced emf opposes the change that is causing emf.

Question 2

Faraday’s Law

Answer 2

Faraday’s Law states that the magnitude of the induced emf is directly proportional to the rate of change of flux linkage

Question 3

Magnetic Field

Answer 3

The region around a magnet where a magnetic force can be experienced

Question 4

Magnetic flux

Units: Weber, φ

Answer 4

The magnetic flux through a region is a measure of the number of field lines cutting through that region

Question 5

Magnetic flux density B

Units: Tesla, T

Answer 5

The magnetic force per unit length per unit current on a current carrying conductor at the right angles to the magnetic flux lines.

Question 6

Tesla

Answer 6

One tesla is the magnetic flux density of a field in which a force of 1N acts on a 1m length of conductor carrying 1A and is perpendicular to the field

Question 7

Magnetic Flux Linkage N

Answer 7

The product of the number of turns N of the coil and the magnetic flux linking each turn.

Question 8

Explain why no work is done by the magnetic field when a charged particle moves in a circular path in the field (3 marks)

Answer 8

Work done = force x distance moved in the direction of the force
The force always acts at right angles to the speed towards the centre of the circle
The force changes the direction of motion but not its speed so the kinetic energy of the particle is unchanged and hence there is no work done.

Question 9

R.M.S Current

Answer 9

For an a.c waveform the r.m.s value of the current is the value of the direct current that would give the same heating effect as using an alternating current in the same resistor