Electromagnetism (M6)

Question 1

Fleming’s left hand rule

Answer 1

Thumb: direction of motion (force)
First finger: direction of the magnetic field
Second finger: direction of the conventional current

Question 2

Right hand grip rule

Answer 2

Thumb points in the direction of the conventional current and the direction of the field is given by the direction in which the fingers are pointing.

Question 3

Faraday’s law

Answer 3

The magnitude of the induced emf is directly proportional to the rate of change of magnetic flux linkage.

E = Nø/t

Question 4

Lenz’s law

Answer 4

The direction of the induced emf or current is always such as to oppose the change producing it.

E = -Nø/t

Question 5

Magnetic flux

Answer 5

The product of the component of the magnetic flux density perpendicular to a given area and that cross-sectional area.

Ø = BAcos¤

Question 6

Magnetic flux density

Answer 6

The strength of a magnetic field
Symbol: B
Unit: Tesla (T)
B = F/IL
F= force
I = current
L = length

Question 7

Magnetic flux linkage

Answer 7

The product of the number of turns N in a coil and the magnetic flux Ø.

Question 8

Step-up transformer

Answer 8

A transformer with more turns on the secondary coil than on the primary coil, and a higher output voltage than input voltage.

Question 9

Step-down transformer

Answer 9

A transformer with fewer turns on the secondary coil than on the primary coil, and a lower output voltage than input voltage.

Question 10

Ideal transformer equations

Answer 10

V1I1 = V2I2 - power is conserved

n2/n1 = V2/V1

Question 11

Technique to determine the magnetic flux density between the poles of a magnet.

Answer 11

N and S poles on a balance with wire through it held up be clamps at the ends.
Current going through the wire by crocodile clips.
Measure L with ruler
Measure I with ammeter
Measure F by change in mass when power turned on F = mg
Increase I by 1A at least 8 times
F = BIL
plot graph of F against I. Gradient is BL. Straight line through origin.