Create a compass

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Dippy is on a journey around the UK. A compass can help him make sure he doesn't get lost on his adventures.

You will need

  • a sewing needle
  • a cork or plastic bottle top
  • a bar magnet
  • sticky tack
  • a shallow dish of water
  • a sharp knife or scissors
  • a towel (optional)
  • a compass (optional, to test your own compass)

Be careful when handling sharp needles and using knives or scissors.

Instructions

  • Cut a slice, 5-10mm thick, from the end of a cork or plastic bottle cap, and set to one side.
  • With the magnet, stroke the needle 50 times from eye to point, rather than back and forth. The needle will be magnetised after 50 strokes. 
  • Attach the magnetised needle on its side to the flat side of the cork slice with some tack. The cork will keep the needle floating on the water.
  • Float the cork in a dish of water. Water creates an almost frictionless surface, which allows the cork to rotate until the north pole of the needle points towards the magnetic North Pole, as shown on a manufactured compass. Keep the dish away from computers and other devices that contain magnets as it can disrupt the field lines.
  • You can then check your result using a manufactured field compass or a smartphone with a compass tool. The needle will slowly lose its magnetic charge over time.

How is a needle magnetised?

Iron, nickel and cobalt contain tiny regions called magnetic domains, in which electrons align in the same direction. These domains point in different directions so tend to cancel each other out.

When one of these metals is exposed to a strong magnetic field the domains are encouraged to align, which turns it into a temporary magnet.

This is how a steel needle (which contains iron) becomes magnetised when stroked by a permanent magnet.

Why does a compass point north?

Once the needle is magnetised it naturally wants to align with the Earth's stronger magnetic field.

Scientists believe this field, called the magnetosphere, is created by electrical currents that are generated by a churning molten iron core deep inside the planet.

It means Earth acts as if it had a bar magnet running through it, with the magnet's south pole located near the planet's geographic north. Since opposites attract, the north pole of a magnetised needle is attracted towards it.