Optional Practical: Flux density


In this practical the flux density of a magnet will be found by measuring the force experienced by a current carrying conductor placed in the field using a digital balance. From the definition of flux density the force experienced by a current carrying conductor in a perpendicular field is given by:


Where B = Flux density
I = Current
L = Length of conductor in the field


  • Set up the apparatus as in the diagram but don’t connect the multi meter to the Nichrome wire until you are ready.
  • Make sure the leads are connected to the correct terminals and set the multi meter to measure up to 10A.
  • Zero the balance using the tare button then test to see if everything is working by touching  the mutimeter probe  to the Nichrome wire. The balance reading should go –ve.

WARNING Depending on the diameter and length of the sample of Nichrome wire it might get hot, be careful not to burn your fingers on the wire.

  • The current through the wire can be varied by moving the connector along the Nichrome wire, try this.  The force should change.
  • By varying the current and measuring the force use a graphical method to determine the flux density of the magnet.  You can compare this with the value obtained with a magnetic field sensor.
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