Fleming's Left-Hand Rule
Get to grips with Fleming's Left-Hand Rule for GCSE Physics with this free worksheet and full mark scheme — Higher-tier exam-style questions with worked answers for AQA, Edexcel and OCR. Fleming's left-hand rule gives the direction of the force, with the thumb, first and second fingers showing motion, field and current.
Free downloads
These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
This is a Higher tier only topic, so there's no Foundation paper — only the Higher worksheet and mark scheme below.
Topic overview
Fleming's left-hand rule gives the direction of the force in the motor effect. This is a Higher-only topic.
Hold the thumb, first finger and second finger of the left hand at right angles to each other. The First finger points in the direction of the magnetic Field, from north to south. The seCond finger points in the direction of the Current, from positive to negative. The thuMb then gives the direction of the Motion, or force.
The mnemonic is First-Field, seCond-Current, thuMb-Motion. It must be the left hand for the motor effect. Using the right hand gives the direction for the generator effect instead, so the two must not be confused.
Revision notes
The rule
Hold the thumb, first finger and second finger of the LEFT hand mutually at right angles.
First finger: magnetic Field, pointing from north to south. seCond finger: Current, from positive to negative. thuMb: Motion, the direction of the force.
Remembering it
The letters help: First-Field, seCond-Current, thuMb-Motion.
It must be the left hand for the motor effect. Practising with an actual hand rather than trying to visualise it is far more reliable in an exam.
Reversing the direction
Reversing either the current or the magnetic field reverses the direction of the force.
Reversing both leaves the force in the original direction, because the two reversals cancel out.
Key points
- Fleming's left-hand rule gives the force direction.
- First finger is the magnetic Field.
- seCond finger is the Current.
- thuMb is the Motion or force.
- Field points from north to south.
- Reversing current or field reverses the force.
Worked examples
Example 1
State what each finger represents in Fleming's left-hand rule. [3 marks]
Model answer
The first finger represents the magnetic field, pointing from north to south (1 mark). The second finger represents the current, from positive to negative (1 mark). The thumb represents the direction of the motion or force (1 mark).
Example 2
Explain what happens to the direction of the force if the current is reversed. [2 marks]
Model answer
The direction of the force is reversed (1 mark), because reversing the current reverses the second finger direction in Fleming's left-hand rule (1 mark).
Example 3
Explain what happens to the force if both the current and the magnetic field are reversed. [2 marks]
Model answer
The force acts in the original direction (1 mark), because the two reversals cancel each other out (1 mark).
Common mistakes
Using the right hand.
The left hand is for the motor effect; the right hand relates to the generator effect.
Pointing the field from south to north.
The field direction is always north to south.
Confusing which finger is which.
Use the letters: First-Field, seCond-Current, thuMb-Motion.
Not holding the fingers at right angles.
All three must be mutually perpendicular for the rule to work.
Exam tips
- Use your actual left hand in the exam.
- Learn the letter mnemonic for the three fingers.
- Check the field runs north to south.
- Remember this is a Higher-only topic.
Key terms
- Fleming's left-hand rule
- A rule giving the force direction in the motor effect.
- Magnetic field direction
- From north to south.
- Conventional current
- Flow from positive to negative.
- Motion
- The direction of the resulting force.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.