physics - topic 12 magnetism and the motor effect

gcse > edexcel > physics > higher > paper 2

12.1 recall that unlike poles attract and like magnetic poles repel

• this principle describes the behaviour of magnets when two magnets are held close together

• opposite poles (north and south) come together because of the force of attraction

• similar poles (north-north or south-south) push away from each other because of the force of repulsion

• the force produced is a non-contact force

12.2 describe the uses of permanent and temporary magnetic materials, including cobalt, steel, iron and nickel

• permanent magnets are made out of permanent magnetic materials, for example steel

• they cannot be turned on or off - they are always magnetic

• they always produce a magnetic field

• temporary magnets are used in electromagnets

• Unlike a permanent magnet, an induced magnet only becomes a magnet when it is placed in a magnetic field. The induced magnetism is quickly lost when the magnet is removed from the magnetic field.

  The iron filings in the image become induced magnets when they are near the bar magnet. Like all induced magnets:

  • they are only attracted by other magnets, they are not repelled

  • they lose most or all of their magnetism when they are removed from the magnetic field

12.3 explain the difference between permanent and induced magnets

12.4 describe the shape and direction of the magnetic field around bar magnets for a uniform field, and relate the strength of the field to the concentration of linres