Magnetic fields

• Current carrying wire place in a magnetic field

  F = BIL
• Magnetic flux Wb

  φ = BA

  B is magnetic flux density (T)
• Magnetic flux density (T)

  Magnetic field strength, B
• Magnetic flux

  Total no. of magnetic field lines passing through a certain area
• Magnetic flux linkage

  Nφ = BAN
• Faradays law

  Magnitude of induced EMF is directly proportional to the rate of change of magnetic flux linkage
• Lenz Law

  Direction of an induced emf will act to oppose the change which caused the emf

  (new B field it creates always opposes the old B field that created it)
• Speed of proton, given B and r

  r = mv/Bq

  v = rBq/m
• Explain why the fin will leave the gap with a much slower speed than it entered the gap.

  • Fin enters the magnetic field of the magnetic it induces a EMF because of the change in magnetic flux linkage
  • Hence, current is produced by the induced EMF
  • Force acts on the fin because of the interaction between the magnetic field from the current and magnet
  • Due to Lenz Law, force will oppose the motion of the fin
• Explain how applying a alternating p.d. across the input coil causes the capacitor to charge.

  • AC current in the input coil
  • Varying B field in input from alternating p.d
  • Hence change in magnetic flux linkage in secondary coil
  • EMF is induced
  • Diode is converts from AC to DC
  • Current is passed to capacity, completing the circuit