AQA GCSE Flemings Left Hand Rule(Physics)
Fleming’s Left Hand Rule
Fleming’s left-hand rule is used to determine the direction of the force acting on a conductor when it carries an electric current and is placed in a magnetic field.
You will often use Fleming’s left hand rule when working with electric motor questions or motor effect questions.
Using Fleming’s left hand rule
Fleming’s left hand rule relates 3 quantities
Magnetic field direction (first finger)
Current direction(second finger)
Direction of force or movement (thumb).
Given two of these you will need to work out the direction of the third quantity.
Example 1
In the example below:
Your first finger should point towards the right as the magnetic field from North to South is from left to right.
Second finger should point downwards as the current is going down the wire
Thumb will point towards you, so the force is towards you. As a result the wire will move towards you.
Example 2
Example 3
Below is an image of an electric motor that we will apply Fleming’s left hand rule to.
In an electric motor a coil (green) spins in a magnetic field.
The current flows in opposite directions on both sides of the coil
On the left hand side of the coil:
Current flows towards you. so 2nd finger should point towards you.
Magnetic field is North to South (left to right), so first finger should point towards wall on right.
Thumb should point up towards ceiling. Coil on left side experiences an up force.
On the right hand side of the coil:
Current is flowing away from you in coil, so second finger points towards the wall infront of you.
First finger is still pointing to right as magnetic field is in same direction.
Thumb should now point downwards towards the floor, coil on the right hand side experiences a downwards force.
Practice Question
1.What is Fleming’s left hand rule used to determine?
2.State what the following represent:
2a First finger………………………
2b Second finger……………………..
2c Thumb………………………………
3. Use the following diagram to predict the direction of force that the wire experiences
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