Magnetism + double content for electromagnetism

Magnets ___ and ___ other magnets

Attract and repel

• Depending on the positioning of the poles

Magnets are able to ___ objects made from magnetic materials.

What are the magnetic materials? What are the two types?

Attract

Iron, steel, nickel, cobalt and neodynium

Magnetically materials can be magnetically soft (temporary magnets) or magnetically hard (permanent magnets)

What are magnetically soft materials?

What are magnetically hard materials?

• Magnetically soft materials are easy to magnetise, easily lose their magnetism (temporarily magnetised) — they lose it when the field is removed

  • Usually iron

• Magnetically hard materials are difficult to magnetise, do not easily lose their magnetism (permanently magnetised)

  • They are usually steel, nickel, cobalt, neodynium

What is a magnetic field?

Region of space around a magnet where a magnetic force acts on another magnet or on a magnetic material

What are magnetic field lines?

They are used to:

• Show the shape of the magnetic field

• Show the direction of the magnetic force — the field lines ‘travel’ from north to south (use arrows)

• Show the strength of the magnetic field — the field lines are closest together where the magnetic field is the strongest

  • Lines are closest at the poles

  • Make sure the lines get further apart as the distance from the magnet increases

What are the rules when drawing magnetic field lines?

• Lines always go from north to south

• Two magnetic field lines must never touch or cross other field lines

Practical: investigate the magnetic field patterns of bar magnets

What are the two ways?

• Using iron filings

• Using compasses

Describe the methods

What happens if you break a magnet in half?

You will have two mini magnets: both magnets have north and south poles

What is this type of magnetic field called? What is it?

Uniform magnetic field

• Lines are parallel and equidistant (equally spaced)

• This means same strength, same direction everywhere in this region

What type of magnet can we use to create a uniform magnetic field?

An uniform field is created when two opposite poles are held close together

A U-shaped permanent magnet

How do we induce magnetism from, for example, a magnetic material like an iron nail?

We place the object inside a magnetic field

• Magnetically hard materials like steel will retain some of its magnetism after the magnet is removed

• Magnetically soft materials like iron will lose their magnetism when the magnetic field is removed

How do we test whether a material is a magnet or a magnetic material?

• If it can be repelled by the known magnet then the material itself is a magnet

• If it can only be attracted and not repelled then it is a magnetic material

When magnetism is induced in a marieral:

• The end of the material closest to the magnet will have the opposite pole to magnets pole closest to the material

• One end becomes the north pole and the other becomes a south pole

What is created when there is a current in a wire (or any conductor) + describe? What is this called?

A magnetic field is created around it. The field around the wire is weak and circular in shape (magnetic field is made up of concentric circles)

This is called electromagnetism

What does the magnetic field being made up of concentric circles mean?

What happens to these circles as the distance from the wire increases? What does this show?

It indicates that the magnetic field around a current carrying wire has no poles

• As the distance from the wire increases the circles get further apart

  • This shows that the magnetic field is strongest closest to the wire and gets weaker as the distance from the wire increases

How can we show the shape and direction of the magnetic field around a current-carrying wire?

What happens when we change the direction of the current?

Using iron filings AND compasses

Reversing the direction of the current reverses the direction of the magnetic field

How can we work out the direction of the field?

Using the right hand thumb rule

• NOT LEFT

If there is no current there is ___

What are the factors affecting field strength? Draw two diagrams to interpret this

No current = no magnetic field

Factors

• Size of current: larger current produces a stronger magnetic field

• Distance from the long straight conductor: greater the distance, the weaker the magnetic field

• REMEMBER to draw the lines at the correct distance in each scenario

What is meant by the term ‘polarity’?

Term used to describe which parts of a magnet are north or south or which parts of an electrical circuit are positive or negative