Revision Notes

4.6.8 Force on a Charged Particle

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How a Magnetic Field Deflects a Charged Particle

  • When a charged particle passes through a magnetic field, the field can exert a force on the particle, deflecting it
  • This happens because the moving charge forms a current


Deflected particle, IGCSE & GCSE Physics revision notes

When a charged particle (such as an electron) enters a magnetic field, it is deflected by the field


  • The force is always at 90 degrees to both the direction of travel and the magnetic field lines, and can be worked out by using the left-hand rule
    • However, if the particle has a negative charge (such as an electron), then the second finger (the current) must point in the opposite direction to the direction of travel
  • The deflection of charged particles can be demonstrated either by using a cathode ray tube and a pair of magnets, or by passing a collimated beam of beta particles (high energy electrons) between the poles of a horseshoe magnet

(Note: A cathode ray tube fires electrons at high speed towards a target. Old TV sets contained cathode ray tubes, but you must be careful using these, as holding a magnet to the screen can permanently affect the image)

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Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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