Magnetic Fields in Solenoids (Edexcel GCSE Combined Science) : Revision Note

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The Field around a Solenoid

  • When a wire is looped into a coil, the magnetic field lines circle around each part of the coil, passing through the centre of it

flat-celular-coil, IGCSE & GCSE Physics revision notes

Diagram showing the magnetic field around a flat circular coil

  • To increase the strength of the magnetic field around the wire it should be coiled to form a solenoid

  • The magnetic field around the solenoid is similar to that of a bar magnet

Field Lines Solenoid, downloadable IGCSE & GCSE Physics revision notes

Magnetic field around and through a solenoid

  • The magnetic field inside the solenoid is strong and uniform

  • Inside a solenoid (an example of an electromagnet) the fields from individual coils

    • Add together to form a very strong almost uniform field along the centre of the solenoid

    • Cancel to give a weaker field outside the solenoid

  • One end of the solenoid behaves like the north pole of a magnet; the other side behaves like the south pole

    • To work out the polarity of each end of the solenoid it needs to be viewed from the end

    • If the current is travelling around in a clockwise direction then it is the south pole

    • If the current is travelling around in an anticlockwise direction then it is the north pole

  • If the current changes direction then the north and south poles will be reversed

  • If there is no current flowing through the wire then there will be no magnetic field produced around or through the solenoid

Direction of field solenoid, downloadable AS & A Level Physics revision notes

Poles of a Solenoid

  • The strength of the magnetic field produced around a solenoid can be increased by:

    • Increasing the size of the current which is flowing through the wire

    • Increasing the number of turns in the coil in a given length

    • Reducing the length of the wire and maintaining the number of turns

    • Adding an iron core through the centre of the coils

  • The iron core will become an induced magnet when current is flowing through the coils

  • The magnetic field produced from the solenoid and the iron core will create a much stronger magnet overall

Examiner Tips and Tricks

Remember the term ‘uniform field’ means a field which has the same strength and direction at all points. This is represented by parallel field lines. When discussing the strength of an electromagnet, avoid saying “add more coils”:

The coil describes the overall object – the individual loops of wire should be referred to as turns.

The correct phrase to use is “add more turns to the coil”.

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Ashika

Author: Ashika

Expertise: Physics Content Creator

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.

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