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Magnetism and the Motor Effect

Plotting compasses and the Earth's magnetic field

  • 3 things to know
  • Paper 2

Overview

Mapping a field with a plotting compass, what the needle lines up with, evidence that the Earth has a magnetic field, the pole near geographic north, and the molten outer core.

What you need to know

Answer each one before you reveal it.

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Key term

A plotting compass is placed just beyond the north pole of a bar magnet. State which end of its needle points away from that pole.

Key term

State one precaution needed when plotting compasses are used to map a magnetic field.

Key term

Explain how a plotting compass shows that the Earth produces a magnetic field.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Describe how a plotting compass is used to find the shape of the magnetic field around a bar magnet.

    Model answer

    The compass is placed near one pole, the direction its needle settles in is recorded, and it is moved on step by step to follow the line round.

  2. 2

    State what the needle of a plotting compass lines up with.

    Model answer

    It lines up with the direction of the magnetic field at that point.

  3. 3

    A plotting compass is placed just beyond the north pole of a bar magnet. State which end of its needle points away from that pole.

    Model answer

    The north-seeking end points away from the magnet's north pole.

  4. 4

    State one precaution needed when plotting compasses are used to map a magnetic field.

    Model answer

    Keep other magnets and iron objects well away, because they distort the field being mapped.

  5. 5

    Describe what a row of plotting compasses shows when they are placed on a bench far from any magnet.

    Model answer

    They all settle pointing the same way, along the Earth's magnetic field.

  6. 6

    Explain how a plotting compass shows that the Earth produces a magnetic field.

    Model answer

    A freely turning needle always settles in the same direction even when no magnet is nearby, so a field must act on it.

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