Fleming's Left-Hand Rule (HT only)
- 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:
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.
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
Examiner 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!
