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AKA: Mariner's compass

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Fig 1: Three sizes of commercially available compasses
Fig 1
Fig 2


An instrument which uses a magnetised pointer to determine direction on earth.


Compasses used in school science are usually very simple in construction, consisting of a magnetised pointer which is free to rotate on a pivot. More expensive types usually used in orienteering may involve a liquid filled chamber with floating 'needle'. Various types can be purchased from most lab suppliers.

Compasses are often used in electromagnet-making and ‘magnet’ lessons to show the effect of the magnetic field. Several tiny compassed placed around a permanent magnet can quite effectively show the shape of the field.

The tiny compasses (usually around 2-3cm across) are inexpensive but vary in their degree of accuracy. After a lot of use the pointers may not revolve fluidly enough. They are also very small. Slightly larger compasses are more robust but are slightly more expensive. Choosing which type is best for your school will depend on both budget and application.

The N, S, E and W points on a compass are called 'cardinal points', the points between them; NE, SW etc are referred to as 'intercardinal points.'

The pointer end (either a point or red end) always points to the North.


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