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Magnetism and the Motor Effect

Solenoids and electromagnets

  • 3 things to know
  • Paper 6

Overview

What a solenoid is, the strong uniform field inside it and the weak field outside, its bar-magnet field shape, strengthening an electromagnet with more current, more turns or an iron core, and reversing its poles.

What you need to know

Answer each one before you reveal it.

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Key term

What is a solenoid, why is the field strong inside and weak outside the coil, and how can an electromagnet be made stronger?

Key term

State what a solenoid is.

Key term

Explain why the magnetic field inside a solenoid is so strong.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State what a solenoid is.

    Model answer

    A solenoid is a long coil of wire that produces a magnetic field when a current flows in it.

  2. 2

    Describe the magnetic field inside a current-carrying solenoid.

    Model answer

    It is strong and almost uniform, running straight along the axis of the coil.

  3. 3

    Explain why the magnetic field inside a solenoid is so strong.

    Model answer

    Inside the coil the fields from all the separate turns point the same way, so they add together.

  4. 4

    Explain why the magnetic field outside a solenoid is weak.

    Model answer

    Outside the coil the fields from neighbouring turns point in opposite directions, so they largely cancel.

  5. 5

    Describe the shape of the magnetic field outside a solenoid.

    Model answer

    It has the same shape as the field of a bar magnet, with a north pole at one end and a south pole at the other.

  6. 6

    State two ways of increasing the strength of an electromagnet made from a solenoid.

    Model answer

    Increase the current, or wind more turns of wire onto the coil.

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