What is meant by the B-field at a point?

The B-field, or magnetic flux density, is a vector quantity whose magnitude is the force per unit current per unit length on a straight conductor placed at right angles to the field at that point.

State the unit of magnetic flux and its equivalent in tesla and metres.

The unit is the weber (Wb), and 1 Wb is equal to 1 T m².

A uniform field of flux density 0.25 T passes at right angles through a coil of cross-sectional area 4.0 × 10⁻³ m². Calculate the flux through the coil.

Φ = BA = 0.25 × 4.0 × 10⁻³ = 1.0 × 10⁻³ Wb.

A coil of 500 turns encloses a flux of 1.0 × 10⁻³ Wb. Calculate the flux linkage.

Flux linkage = NΦ = 500 × 1.0 × 10⁻³ = 0.50 Wb-turns.

OCR A-Level Physics B H557

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Electromagnetism

Magnetic flux, B-fields and flux linkage

3 things to know
Components 01, 02 and 03

Overview

Recall questions on the B-field and the tesla, magnetic flux Φ = BA and the weber, flux linkage NΦ, a coil turned in a field, the continuity of flux lines and why they never cross, line spacing, and the fields of a bar magnet, a solenoid, a long straight wire and a uniform field.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why does the flux through a coil fall when the coil is turned so that its plane lies along the field lines?

Key term

State the unit of magnetic flux density and express it in SI base units.

Key term

Define magnetic flux and give the equation used for a uniform field.

Questions from this subtopic

Each one with the model answer underneath.

1
What is meant by the B-field at a point?
Model answer
The B-field, or magnetic flux density, is a vector quantity whose magnitude is the force per unit current per unit length on a straight conductor placed at right angles to the field at that point.
2
State the unit of magnetic flux density and express it in SI base units.
Model answer
The unit is the tesla (T), and 1 T is equal to 1 kg s⁻² A⁻¹.
3
Define magnetic flux and give the equation used for a uniform field.
Model answer
Magnetic flux is the product of magnetic flux density and the area it passes through at right angles, Φ = BA.
4
State the unit of magnetic flux and its equivalent in tesla and metres.
Model answer
The unit is the weber (Wb), and 1 Wb is equal to 1 T m².
5
A uniform field of flux density 0.25 T passes at right angles through a coil of cross-sectional area 4.0 × 10⁻³ m². Calculate the flux through the coil.
Model answer
Φ = BA = 0.25 × 4.0 × 10⁻³ = 1.0 × 10⁻³ Wb.
6
A coil of 500 turns encloses a flux of 1.0 × 10⁻³ Wb. Calculate the flux linkage.
Model answer
Flux linkage = NΦ = 500 × 1.0 × 10⁻³ = 0.50 Wb-turns.

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