Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Recall and use Fleming’s left-hand rule to represent the relative…
Full specification wording
Topic 12 – Magnetism and the motor effect: 12.12 Recall and use Fleming’s left-hand rule to represent the relative directions of the force, the current and the magnetic field for cases where they are mutually perpendicular
Fleming's left-hand rule gives the three directions in a motor effect situation.
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 12 of 13
Study notes
From the checked teaching notes for this specification point.
The idea
Fleming's left-hand rule gives the three directions in a motor effect situation. Hold your left hand with the thumb, first finger and second finger all at right angles to each other. Point the first finger in the direction of the magnetic field, from north to south. Point the second finger in the direction of the current. Your thumb then points in the direction of the force on the conductor. The rule only works cleanly when the three directions are mutually perpendicular, so check that the field, current and force are all at right angles before applying it. In a multiple-choice question you may be given two directions and asked for the third, or shown a diagram and asked which finger represents which quantity. Recall the mapping first finger = field, second finger = current, thumb = force, then apply it to the options.
What earns the marks
- Recalls that the first finger represents the magnetic field, the second finger the current and the thumb the force.
- Applies the rule to find the direction of the force when the field and current directions are given.
- Recognises that the rule applies when the force, current and magnetic field are mutually perpendicular.
- Uses the left hand, not the right hand, when applying the rule.
Common mistakes and how to put them right
Uses the right hand instead of the left.
Put it right: Fleming's left-hand rule uses the left hand.
Swaps the roles of the first and second fingers.
Put it right: Keep first finger for field and second finger for current.
Applies the rule when the directions are not mutually perpendicular.
Put it right: Check the right angles first.
Exam tips
- Say the mapping to yourself: first finger field, second finger current, thumb force.
- Check the question states the directions are at right angles before using the rule.
- Use the diagram's arrows to fix two directions, then read off the third from your hand.
Try the lesson
The start of the Topic 12 – Magnetism and the motor effect: 12.12 Recall and use Fleming’s left-hand rule to represent the relative directions of the force, the current and the magnetic field for cases where they are mutually perpendicular lesson, made from checked teaching notes for this specification point.
Have a go first
In Fleming's left-hand rule, what does the thumb represent?
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