AQA GCSE Physics

Revision Notes

7.2.3 Fleming's Left-Hand Rule

Higher Tier Only

Fleming's Left-Hand Rule

  • The direction of the force (aka the thrust) on a current carrying wire depends on the direction of the current and the direction of the magnetic field
  • All three will be perpendicular to each other
    • This means that sometimes the force could be into and out of the page (in 3D)
  • The direction of the force (or thrust) can be worked out by using Fleming’s left-hand rule:

Flemings Left Hand Rule, downloadable IGCSE & GCSE Physics revision notes

Fleming’s Left-Hand Rule can be used to determine directions of the force, magnetic field and current

Worked Example

Use Fleming’s left-hand rule to show that if the current-carrying wire is placed into the magnetic field between the poles of the magnet, as shown below, there will be a downwards force acting on the wire.

WE Flemings LHR Question Image, downloadable IGCSE & GCSE Physics revision notes

Step 1: Determine the direction of the magnetic field

    • Start by pointing your First Finger in the direction of the (magnetic) Field.

Step 2: Determine the direction of the current

    • Now rotate your hand around the first finger so that the seCond finger points in the direction of the Current

Step 3: Determine the direction of the force

    • The THumb will now be pointing in the direction of the THrust (the force)
    • Therefore, this will be the direction in which the wire will move

WE Flemings LHR Answer Image, downloadable IGCSE & GCSE Physics revision notes

Exam Tip

Remember that the magnetic field is always in the direction from North to South and current is always in the direction of a positive terminal to a negative terminal.

Feel free to use Fleming’s left hand rule in your exam, just don’t make it too obvious or distracting for other students!

Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
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