07 - Electric and Magnetic Fields

Question 1

7. Explain why the current of a rotating coil in a magnetic field rises to a maximum then decreases.

Answer 1

Initial current is equal to the battery EMF /R
Coil rotates
Movement of coil changes the field
Which induces an EMF according to Faraday’s Law
The EMF opposes original EMF according to Lenz’s Law
The faster the coil rotates the larger the opposing EMF

Question 2

7. Explain how a higher PD is produced across the secondary coil

Answer 2

Alternating current in primary produces an alternating
Magnetic field
The magnetic field is linked to the secondary coil by the iron core
The changing magnetic field induces an EMF in the secondary coil
More turns on the secondary coil will increase the rate of change of flux linkage according to faraday’s law.

v1/v2=n1/n2

Question 3

7. Velocity of the glider with aluminium sheet moving towards a region of uniform magnetic field

magnetic flux perpendicular to aluminium sheet

Answer 3

Enters magnetic field- decreasing
Within magnetic field- constant
Leave magnetic field- decreasing

Question 4

7. Explain why electrons will collect at the top edge of the slice of semiconductor

Question 5

7. Describe how the device can be used as both a generator and an electric motor

Answer 5

Generator:
Rotated coil
cuts magnetic flux
induces EMF

Motor:
current provided to coil
force on sides of coil that are perpendicular to magnetic field
rotate coil as forces provide a moment