Properties of Magnets

invisible man wearing jacket,tie and old style hat but no face

© Marian Beck, Flickr

In this article we learn how a magnet’s poles can both attract and repel.

  • What is a magnet?

A magnet is anything that produces a magnetic field. Can you see the magnetic field surrounding the bar magnet below? No? Why not?

bar magnet with poles in red and green

What is a magnetic field? Science experiments using a bar magnet

A magnetic field exerts an invisible force in the space surrounding a magnet. This invisible force can pull other magnetized metals (such as iron) towards it and can attract or repel other magnets. If we can’t see a magnetic field, how do we know what it ‘looks’ like?

Invisible man with bandages on head talking to woman taken from 1933 film

Click for slide show

Just as we can ‘see’ the outline of  the invisible man’s head through his bandages, so we can ‘see’ a magnetic field if we conduct the following science experiment using iron filings:

Place a bar magnet under a piece of paper. Sprinkle some iron filings (thousands of tiny pieces of iron) on top of the paper. What do you notice?

iron filings on bar magnet showing lines of magnetic field

The iron filings have interacted with the magnet’s magnetic field to produce a pattern that should look very much like the image above.

  • The pattern made by the iron filings has been drawn in the diagram below. What do you notice?

bar magnet with diagram of magnetic field

The arrows show the direction of attraction of each line of force. The direction of attraction is always from north to south. These lines of force originate at the north pole, travel through space and enter the magnet through the south pole. The lines of force never cross each other (intersect). The magnetic field is strongest where the lines of force are closest together.

  • If you look at this science experiments animation at the NDT Resource Center, you will see the different ways in which a metal sphere reacts after being placed in a ‘magnetic field’.

What is a magnetic field? Science experiments using two bar magnets

  • Now place two bar magnets end to end with south poles touching. What will happen next? What is the direction of force going to be?

two bar magnets with south poles touching

  • Next place two bar magnets end to end with their north and south poles facing each other and slightly apart. What is going to happen? What will the direction of force be?

 two bar magnets on wheels north to south attraction

  • At the NDT Resource Center look at the results of your experiments to see if the predictions you made were correct.(Experiments 2 and 3)
  • Look at the diagram of two bar magnets below. Can you tell the north and south poles by the direction of the lines of force? Are the two magnets being attracted to each other or repelled from each other?

two bar magnet north to south attraction showing magnetic fields. Poles not shown

  • What conclusions can you draw from the diagram below? Can you compare the magnetic fields of both these diagrams?

 two bar magnets north to north showing magnetic fields repelling

Finally, remember the rules!

tiger and dog sitting happilytogether with words,'opposite poles attract!'

polar bears play fighting with words,"same poles repel!"

 

 

 

 

 

 

World of Science

  • You can investigate the patterns of different magnetic fields at Magnet Man.
  • Free online science resources and activity worksheets at Primaryresources.co.uk
  • Fun science quiz about magnetism at Quia.com
  • Interesting science facts at Npr.org – did you know that dogs poop along a north-south axis that lines up with the Earth’s magnetic field?
  • Magnets are everywhere- check out these fun facts about where magnets can be found in the home First4magnets.com
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