Calculate the force exerted between the magnet and coil

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Jennifer Harris

Centre No.

Candidate No.

Physics Planning paper 15/03/02

Apparatus

  • Ammeter
  • Bar magnet
  • Coil
  • Connecting wires
  • Metre Rule
  • Power supply (0-12V d.c. supply)
  • String – 2 pieces of equal length 20 cm
  • Set of masses ranging from 1g to 50g
  • Spirit level
  • Blocks of wood
  • Variable resistor

In my experiment I shall set up the apparatus as above.  I have chosen to use a piece of wire which is 2m long and shall be wrapped round a cardboard tube so that it has 200 complete turns which will directly next to each other.  I have chosen to leave no gaps as then the spacing between them will be equal which will mean the intensity of magnetism will be the same throughout the coil.

To calculate the force exerted between the magnet and coil I shall be using the principle of moments.  My metre stick shall be pivoted exactly in the centre (at 50cm mark) to make my measurements more accurate.  I shall then attach the magnet to the left hand end of the metre stick with string; the string will be of length 20cm and marked at every 1cm interval as will the magnet.  On the right hand end of the metre rule I shall place a piece of string also of 20 cm along to the end of the piece of the string I shall attach masses until the metre becomes balanced and is in equilibrium.  I would use the spirit level for extra accuracy to guarantee it was perfectly balanced.  I would then calculate the force acting on the magnet when there was not a current running through the coil.  To calculate the force I would use the equation for the principle of moments.

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FORCE= MASS x PEPENDICULAR DISTANCE FROM ACTING FORCE

e.g.

Say that a mass of 20g was placed on the right hand side and the distance x was 50cm then:-

FORCE= MASS x PEPENDICULAR DISTANCE FROM ACTING FORCE

              = (20/1000) x (50/1000)

              = 0.001 N

Therefore due to equal and opposite forces the force downwards being caused by the magnet is the same as the force being caused downwards by the mass as they are in equilibrium.

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