Electromagnets and Magnetic Fields

Magnets and Electromagnets

Permanent Magnets

Definition: A magnet that retains its magnetism after being removed from an external magnetic field.

Not all metals are magnetic

• Iron

• Cobalt

• Nickel

• (Steel - an alloy of metals that contains Iron)

Magnetic Fields

Definition: A magnetic field is the region around a magnet where a force acts on another magnet or on a magnetic material.

The Earth's magnetic field

• The Earth behaves as if it contains a giant magnet. It produces a magnetic field in which the field lines are most concentrated at the poles.

• This magnetic field can be detected using magnetic materials or magnets.

  
  

4 Rules of field lines

• 1. Field lines never cross

• 1. field lines run North to South

• 1. field lines are continuous

• 1. The closer the field lines are to each other the stronger the magnetic field is. Field lines are strongest at each Pole (North and South)

Rules of magnetism

Like Poles repel each other ( North - North and South - South)

Unlike Poles attract each other (North - South)

A compass

• a magnetic needle mounted on a pivot (so it can turn freely)

• a dial to show the direction

The Compass

• The north pole (north-seeking pole) of the compass needle points towards the Earth’s north pole. If the needle points to the N on the dial, you know that the compass is pointing north. This lets you navigate outdoors using a map

Question?????

If the North Seeking Pole of the compass needle is attracted to NORTH, what does that mean about the north seeking compass needle?

Open Ended

Can you explain what a magnetic field is?

Multiple Choice

What are the two poles on a magnetic?

• East and West

• North and South

• Red and Blue

Multiple Choice

In which direction to magnetic field lines run?

• South to North

• North to South

• East to West

• West to East

Multiple Choice

Like Poles.....

• attract

• repel

• do nothing

Multiple Choice

Unlike Poles.....

• attract

• repel

• do nothing

Multiple Choice

At which point around a magnet is the magnetic field the strongest?

• its the same everywhere

• North pole

• South pole

• North and South poles

Open Ended

If the North Seeking Pole of the compass needle is attracted to directional NORTH, what does that mean about the north seeking compass needle?

Electromagnets

Electromagnet definition: A device consisting of an iron or steel core that is magnetised by electric current in a coil that surrounds it. 

Electromagnets

• When an electric current flows in a wire, it creates a magnetic field around the wire.

• This effect can be used to make an electromagnet. A simple electromagnet comprises a length of wire turned into a coil and connected to a battery or power supply.

  
  

Electric bell. 1

• The switch is open and the metal arm is away from the gong.

Electric Bell. 2

The switch is closed. An electric current flows through the electromagnet, producing a magnetic field.

Electric Bell. 3

The metal arm is attracted to the electromagnet. It hits the gong which makes a sound. The circuit is broken and the electromagnet turns off.

Electric Bell. 4

The metal arm springs back. The contacts touch and the circuit is complete again.

Electromagnets have some advantages over permanent magnets.

• For example:

  they can be turned on and off the strength of the magnetic field can be varied

• These properties make electromagnets useful for picking up scrap iron and steel in scrapyards.

Open Ended

What is an electromagnet?

Open Ended

What 3 things can you do to increase the strength of an electromagnet?

Open Ended

Give two examples where electromagnets are used in every day life?

Multiple Choice

Why is an advantage of an electromagnet over a permanent magnet?

• used to control high voltages

• cheaper

• lighter

• can find them in more places