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6.2.1Magnetism and Electromagnetism

Electromagnetic Induction

5 min read 4 parts Lesson 13 of 16 1 quiz

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Section 1 of 4The Generator Effect

6.2.1 Electromagnetic Induction

Induction is the reverse of the motor effect: movement produces electricity rather than electricity producing movement.

Induced potential difference
  • A potential difference appears across a conductor when it moves through a magnetic field,
    • or when a magnetic field changes through it.
Relative motion
  • The effect depends on relative movement, so moving the magnet while holding the coil still gives the same result as moving the coil.
Motor effect contrast
  • The motor effect converts electrical energy into movement, whereas induction converts movement into electrical energy.
Induced current
  • If the conductor is part of a complete circuit, the induced potential difference drives a current round that circuit.

Section 2 of 4Factors Affecting the Induced Voltage

The induced potential difference depends on how quickly field lines are cut.

1
Moving the magnet or the coil faster increases the rate at which field lines are cut, so the induced potential difference increases.
2
Using a stronger magnet means more field lines are cut, so a larger potential difference is induced.
3
Adding more turns to the coil increases the induced potential difference, because each turn cuts the field lines.
4
Reversing the direction of motion reverses the direction of the induced potential difference and of any current.
5
Holding the magnet still inside a coil induces no potential difference, because no field lines are being cut.

Section 3 of 4Worked Example

Question

  • A bar magnet is pushed quickly into a coil, and then pushed slowly into the same coil.
  • Compare the induced potential differences.

  1. Recall that the induced potential difference depends on the rate at which field lines are cut.
  2. A quick push cuts the field lines faster than a slow push.
  3. So the quick push induces a larger potential difference than the slow push.

Answer The quick push induces a larger potential difference, because the field lines are cut at a greater rate.

Section 4 of 4Exam Checklist & Tips

6.2.1 – Key Points for the Exam

  • Electromagnetic induction The production of a potential difference in a conductor by a changing magnetic field or by relative motion.
  • Generator effect The production of an induced potential difference when a conductor moves through a magnetic field.
  • Induced potential difference A potential difference produced by cutting magnetic field lines or by a changing field.
  • Relative motion Movement of a conductor compared with a magnetic field, which is needed to induce a voltage.

Common Mistakes

  • Saying that a magnetic field alone induces a potential difference; a change or relative movement is required.
  • Stating that the motor effect and the generator effect both convert electrical energy into movement.
  • Claiming a stationary magnet inside a coil induces a potential difference.
  • Forgetting that a potential difference is induced even when the conductor is not in a complete circuit, although no current flows.
Transformer Golden Equations Physics Standard

Transformer Turns Ratio & Efficiency

Ratio: Vp / Vs = Np / Ns = Is / Ip

  • Step-up reduces grid thermal loss (P = I2R).
  • Laminated core prevents eddy currents.