Magnetism_01B

How can a permanent magnet be demagnetised?

• cool the magnet for a long time

• hit the magnet repeatedly with a hammer

• leave the magnet in a coil which carries direct current

• pass a small current through the magnet

Six small compasses are placed around a bar magnet. Which diagram shows the directions in which the compass needles point?

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A student carries out four tests with a magnet. Which result shown is not correct?

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• B

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• D

A copper ball on a horizontal wooden table rolls near the north pole of a bar magnet that is lying on the table. Which diagram shows the most likely path of the ball, as seen from above the table?

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A brass rod is positioned in an east-west direction and a plotting compass is placed at each end, as shown. Which diagram shows the positions of the needles of the plotting compasses?

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How many of the following methods could be used to demagnetise a piece of steel?
heating it until it is red hot;
pulling it from a coil that is carrying an alternating current;
placing it in an east-west direction and hammering it;
putting it in a coil which is carrying a direct current.

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