State the formula for the force on a current-carrying conductor in a magnetic field and define each symbol.

F = BIL sin θ, where F is force, B is magnetic flux density, I is current, L is the length of conductor in the field, and θ is the angle between the conductor and the field direction.

Under what condition does the force on a current-carrying conductor in a magnetic field reach its maximum value?

When the conductor is perpendicular to the magnetic field (θ = 90°), so sin θ = 1.

In the current-balance experiment to measure magnetic flux density, how is the wire positioned relative to the magnet poles?

A wire of known length is placed horizontally between the poles of the magnet, perpendicular to the field.

What instruments are connected to the wire in the current-balance experiment?

The wire is connected to a power supply with an ammeter in series to measure the current.

OCR A-Level Physics A H556

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Electromagnetism

Fleming's left-hand rule and the motor effect

3 things to know
Papers 1, 2 and 3

Overview

Recall questions on Fleming's left-hand rule, the force on a current-carrying conductor F = BIL sin θ with calculations, and the current-balance experiment to measure magnetic flux density.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

In the current-balance experiment, why is the balance zeroed first, what is recorded when current flows, and how is the force on the wire calculated?

Key term

In Fleming's left-hand rule, what does the first finger represent?

Key term

In Fleming's left-hand rule, what does the thumb represent?

Questions from this subtopic

Each one with the model answer underneath.

1
In Fleming's left-hand rule, what does the first finger represent?
Model answer
The direction of the magnetic field (B).
2
In Fleming's left-hand rule, what does the thumb represent?
Model answer
The direction of the force on the conductor, or its motion.
3
State the formula for the force on a current-carrying conductor in a magnetic field and define each symbol.
Model answer
F = BIL sin θ, where F is force, B is magnetic flux density, I is current, L is the length of conductor in the field, and θ is the angle between the conductor and the field direction.
4
Under what condition does the force on a current-carrying conductor in a magnetic field reach its maximum value?
Model answer
When the conductor is perpendicular to the magnetic field (θ = 90°), so sin θ = 1.
5
In the current-balance experiment to measure magnetic flux density, how is the wire positioned relative to the magnet poles?
Model answer
A wire of known length is placed horizontally between the poles of the magnet, perpendicular to the field.
6
What instruments are connected to the wire in the current-balance experiment?
Model answer
The wire is connected to a power supply with an ammeter in series to measure the current.

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