Factors Affecting EM Induction (Edexcel GCSE Physics: Combined Science)

Higher Tier Only

• The size of the induced potential difference is determined by:
  • The speed at which the wire, coil or magnet is moved
  • The number of turns on the coils of wire
  • The size of the coils
  • The strength of the magnetic field

• The direction of the induced potential difference is determined by:
  • The orientation of the poles of the magnet

1. The speed at which the wire, coil or magnet is moved:

• • Increasing the speed will increase the rate at which the magnetic field lines are cut
  • This will increase the induced potential difference

2. The number of turns on the coils in the wire:

• • Increasing the number of turns on the coils in the wire will increase the potential difference induced
  • This is because each coil will cut through the magnetic field lines and the total potential difference induced will be the result of all of the coils cutting the magnetic field lines

3. The size of the coils:

• • Increasing the area of the coils will increase the potential difference induced
  • This is because there will be more wire to cut through the magnetic field lines

4. The strength of the magnetic field:

• • Increasing the strength of the magnetic field will increase the potential difference induced

5. The orientation of the poles of the magnet:

• • Reversing the direction in which the wire, coil or magnet is moved

The Magnetic Field Produced

• The direction of an induced potential difference always opposes the change that produces it
• This means that the magnetic field produced from EM induction also opposes the original change
  • The field will act so that it tries to stop the wire or magnet from moving

• If a magnet is pushed north end first into a coil of wire then the end of the coil closest to the magnet will become a north pole
• Explanation:
  • Due to the generator effect, a potential difference will be induced in the coil
  • The induced potential difference always opposes the change that produces it
  • The coil will apply a force to oppose the magnet being pushed into the coil
  • Therefore, the end of the coil closest to the magnet will become a north pole
  • This means it will repel the north pole of the magnet

Magnet being pushed into a coil of wire

• If a magnet is now pulled away from the coil of wire then the end of the coil closest to the magnet will become a south pole
• Explanation:
  • Due to the generator effect, a potential difference will be induced in the coil
  • The induced potential difference always opposes the change that produces it
  • The coil will apply a force to oppose the magnet being pulled away from the coil
  • Therefore, the end of the coil closest to the magnet will become a south pole

  • This means it will attract the north pole of the magnet

Magnet being pulled away from a coil of wire

Part (a)

ANSWER:  C

• • C is correct because there the magnet is stationary
  • This means there is no relative movement between the coil and the magnetic field, therefore there are no magnetic field lines being cut
  • If the magnetic field lines are not being cut then there will not be a potential difference induced

• • A, B & D are incorrect because a deflection on the voltmeter would indicate that a potential difference has been induced
  • This could only happen if there was relative movement between the coil and the magnetic field

Part (b)

ANSWER:  A

• • A is correct because the magnet is moving relative to the coil
  • This means that the needle on the voltmeter will deflect
  • The needle on the voltmeter will deflect to the left because it is moving in the opposite direction to the diagram
  • When the direction of the magnetic field lines are reversed, the direction of the induced current will be reversed

• • B is incorrect because the magnet is moving in the opposite direction to the diagram
  • This means it will deflect in the opposite direction (to the left)

• • C is incorrect because the magnet is moving
  • This means that a potential difference will be induced in the coil and the needle on the voltmeter will deflect

• • D is incorrect because the magnet only moves in one direction
  • This means the voltmeter should only deflect in one direction only