Magnetism and Electromagnetism

What is a magnet?

any material or object that produces a magnetic field

Which direction do the magnetic fields go?

• out of the North

• into the South

Where are the magnetic forces the strongest at?

The poles of the magnet

What happens when two of the same poles are close together?

There is a force of repulsion

What is the difference between a permanent and induced magent?

• permanent produces its own magentic field

• induced becomes a magent when places in a magentic field

When do permanent magnets attract or repel?

When they are close together

What’s a rule with induced magnetism?

• it always causes a force of attraction

• if permanent magnet is taken away then the induced magnets lose most or all of their magnetism quickly

What are examples of magnetic materials?

iron, cobalt, nickel and steel

What is the magentic field?

the region around the magnet where a force acts on another magnet or a magnetic material

Which direction does magnetic field run?

North to South

Why does a magnetic compass always point in the North-South direction when it is held away from other magnets?

• the earth has its own magnetic field

• due to the earth’s core

What happens when a current flows through a conducting wire?

a magnetic field is produced around the wire

What does the right hand rule mean?

• thumb is direction of the conventional current

• fingers are pointing in the direction of the magnetic field

What is another way to increase the strength of the magnetic field?

• coil the wire (solenoid)

• when current is turned on, there is a strong and uniform magnetic field inside the soleniod

How can the strength of the magnetic field produced by a solenoid be increased?

• increase size of current

• increased number of turns on the coil

• placing a piece of iron inside the solenoid

Why are electromagnets useful?

• strength of the magnetic field can be changed by changing the size of the current

• can be turned on or off

What’s fleming’s left hand rule?

• Thumb is direction of the force

• First finger is direction of magnetic field

• Second finger in direction of conventional current

What happens if the conductor is parallel to the magnetic field?

it will not experience a force

What is the motor effect?

when a conductor such as a wire is carrying a current it experiences a force in a magnetic field

Whats the problem with the motor effect?

• force on left hand side acts upwards force on right hand side acts downwards

• so coil spins clockwise

• once it reaches 180 degrees the current travels in the opposite direction so forces acting on each side of the coil have swapped direction

• so now left force acts downwards and force on right force acts upwards

• so the coil turns anticlockwise and flips back where it started

• so it isn’t useful

How can we stop the motor effect not working?

• by switching the direction of the current every half turn

• using a split-ring commutator

What does the split-ring commutator do?

• swaps the positive and negative connections every half turn

• so direction of the current also swaps every half turn

• so force is acting on the coil always in the same direction

• so it will rotate in the same direction all the time