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
- the magnetic field
- All three will be perpendicular to each other in Fleming's left-hand rule questions
- 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 the directions of the force, magnetic field and current
Worked example
A current-carrying wire is placed into the magnetic field between the poles of the magnet, as shown in the diagram.
Use Fleming’s left-hand rule to show that there will be a downward force acting on the wire.
Answer:
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.
Feel free to use your hands when answering Fleming's left hand rule questions, just don't make it too obvious or distracting for other students!
