electromagnets

Question 1

what is electromagnetic induction?

Answer 1

generation of an emf when:
the magnetic flux linkage on a coil changes
or
a conductor cuts across magnetic field lines

Question 2

what is generator effect?

Answer 2

force applied to a wire making it in a magnetic field induces a potential difference

Question 3

what happens to electrons if the wire is part of a complete circuit

Answer 3

the emf forces electrons round the circuit if the wire is part of a complete circuit

Question 4

how can the induced emf be increased

Answer 4

moving the wire
using a stronger magnet
making the wire into a coil and pushing the magnet in or out of the coil

Question 5

what are two or methods of generating an induced emf

Answer 5

using an electric motor in reverse

using a cycle dynamo

Question 6

how is an emf generated in a cycle dynamo and in an electric motor

Answer 6

there is relative motion between the coil and magnet
in the electric motor coil spins and the magnet is fixed
in the dynamo the magnet spins and the coil is fixed

Question 7

outline how using an electric motor in reverse generates an induced emf

Answer 7

The falling weight makes the motor coil turn between the poles of the magnet in the motor

emf induced in the coil forces a current round the circuit and so causes the lamp to light

Question 8

what does lenz’s law state?

Answer 8

the direction of the induced current is always such that is opposes the change that causes the current