Fleming's left-hand rule (HT only) — AQA GCSE Physics
Test yourself on Fleming's left-hand rule (HT only) with AQA GCSE practice questions.
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Fleming's left-hand rule (HT only) explained
This is Higher tier only. The size of the force follows from F = B I l, so it depends on three things: the magnetic flux density B, which is how strong the magnet's field is, the current I in the conductor, and the length l of the conductor that is inside the field.
Read the full explanation
Double any one of them and the force doubles. That is why a current balance question asking how to increase the force on the wire is answered by using a stronger magnet or by increasing the current. Orientation is a condition rather than a factor: the relationship holds when the conductor is at right angles to the field, and the force falls to zero when the wire lies along the field.
Your focus
- List the three quantities that determine the size of the force on a current carrying conductor.
- Suggest a practical change to an apparatus that increases the force, and explain why it works.
- Explain why reversing the current changes the direction of the force but not its size.
Fleming's left-hand rule (HT only) exam tips
Marking Points
- one mark for naming the strength of the magnetic field, or the magnetic flux density, as a factor
- one mark for naming the size of the current in the conductor as a factor
- one mark for naming the length of conductor inside the magnetic field as a factor
- one mark for suggesting a specific practical change, such as using a stronger magnet or increasing the current
Examiner Tips
- 💡'Suggest one change' means one clear change; a list can be marked on the first answer only.
- 💡Use the equation F = B I l to generate the factors rather than trying to recall a list.
- 💡This content is Higher tier only.
Common Mistakes
- answering 'increase the voltage' without linking it to an increase in current
- naming the total length of the wire rather than the length of it that is inside the field
- listing reversing the current as a way to increase the force, when it only changes the direction
- offering the mass of the wire or the resistance of the circuit as factors