Electromagnetism

Question 1

Why does a wire experience a force as current flows through it in a magnetic field ?

Answer 1

Current creates a magnetic field around the wire
Electromagnetic field around wire interacts with magnet’s magnetic field
Interaction between these 2 magnetic fields creates a force

Question 2

How can strength of this force be increased?

Answer 2

Increase strength of magnetic field by using stronger magnets
Increasing current in wire

Question 3

How can a DC motor be sped up?

Answer 3

Increase current in wire
Use stronger magnetic field by using stronger magnets
Use a soft iron core in the coil
More turns in the coil

Question 4

Describe how a DC motor works

Answer 4

Current creates magnetic field around wire.
Magnetic field from wire interacts with magnetic field of magnets, exerting a force on the coil
Current flows in opposite direction on each side of coil, force pushes one side of coil up and other side down.
Coil rotates until its in vertical position
Split ring commutators swap contacts of coil, reversing direction current flows in, reversing direction the forces act in so the coil continues to rotate.

Question 5

Describe how a loudspeaker works

Answer 5

Alternating current passes through the coil, creating a changing magnetic field around the coil. Magnetic field of coil interacts with magnetic field from magnet, exerting a force on the coil. Force changes direction constantly, causing the coil and cone to oscillate and creating air oscillations or sound waves.

Question 6

Explain left hand rule

Answer 6

Thumb - force
First finger - magnetic field
Second finger - current

Question 7

Describe how voltage is induced in a wire

Answer 7

A coil moves through a magnetic field, cutting magnetic field lines and inducing a voltage in the coil
or
a magnetic field through a coil changes

Question 8

How can you increase induced voltage?

Answer 8

Increase strength of magnet
Increase number of turns on coil
Increase speed of movement

Question 9

Describe how an AC generator works

Answer 9

Generators rotate a coil in a magnetic field
As coil spins, current is induced in the coil. This current changes direction every half turn. Slip rings and brushes ensure contacts don’t swap every half-turn, producing an a.c voltage as the current is constantly changing direction