IGCSEPhysicsOxford AQARevision NotesGenerating & Distributing Electricity & Household UseGenerating ElectricityFactors Affecting Induced Potential Difference

Factors Affecting Induced Potential Difference (Oxford AQA IGCSE Physics)

Revision Note

Factors Affecting Induced Potential Difference

Changing the magnitude of induced p.d.

  • The magnitude of the induced potential difference is determined by:

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

    • Increasing the speed will increase the rate of change of magnetic flux

    • This will increase the induced potential difference

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

    • Increasing the number of turns on the coil in the wire will increase the potential difference induced

    • This is because each turn on the coil will cut through the magnetic field lines and the total potential difference induced will be the result of all of the turns on the coil cutting the magnetic field lines

  3. The size of the coil:

    • Increasing the area of the coil 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

Changing the direction of induced p.d.

  • The polarity of the induced potential difference is reversed if:

  1. The orientation of the poles of the magnet is reversed (i.e. its polarity is reversed)

  2. The direction of motion of the wire, coil or magnet is reversed

Worked Example

A coil rotates in a uniform magnetic field. The number of turns on the coil is then tripled, the strength of the magnet is halved and the frequency of the coil's rotation is doubled.

Describe how the output alternating current is affected by these changes.

Answer: 

  • The number of turns triples, so the magnitude of the induced p.d. is tripled

  • Therefore the output current's magnitude is also tripled, as these are proportional

  • The strength of the magnetic field, however, is halved. This halves the magnitude of the output alternating current

  • Overall, the output current is 1.5× greater in magnitude

  • If the frequency doubles, then the frequency of the alternating current also doubles, or its period halves

Exam Tip

When discussing factors affecting the induced potential difference:

  • Make sure you state:

    • “Add more turns to the coil” instead of “Add more coils”

    • This is because these statements do not mean the same thing

  • Likewise, when referring to the magnet, use the phrase:

    • “A stronger magnet instead of “A bigger magnet”

    • This is because larger magnets are not necessarily stronger

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