Magnetic flux and flux linkage Edexcel International A Level Physics revision
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In plain words
Think of a magnetic field as a stream of lines passing through a loop of wire. Magnetic flux measures how much field is passing through. It is the idea you need before you can understand a generator: a voltage appears whenever that amount changes.
4 things to know
- Magnetic flux Φ = BA, where B is the flux density at right angles to the area A. Unit: the weber (Wb), which is one tesla metre squared.
- If the field is not at right angles to the area, only the part of the field at right angles counts.
- Magnetic flux linkage = NΦ for a coil of N turns, in Wb.
- The flux through a coil changes if the flux density changes, if the area in the field changes, or if the coil is turned.
Worked example
A coil of 200 turns and area 4.0 × 10⁻³ m² is at right angles to a field of flux density 0.050 T. Find the flux through it and the flux linkage.
- Φ = BA = 0.050 × 4.0 × 10⁻³ = 2.0 × 10⁻⁴ Wb.
- Flux linkage = NΦ = 200 × 2.0 × 10⁻⁴.
- = 0.040 Wb.
Tips and tricks
- "Flux density" is flux per unit area: 1 T is 1 Wb/m².
- A coil whose plane lies along the field has no flux through it.
It lands in your notebook with its questions as flashcards.
Magnetic flux and flux linkage: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What is the unit of magnetic flux?
One weber is one tesla metre squared.
What is the magnetic flux through an area A at right angles to a field of flux density B?
Flux density multiplied by area.
What is the flux linkage of a coil of N turns with a flux Φ through each?
Each turn is linked by the same flux.
The plane of a coil lies parallel to a magnetic field. What is the flux through the coil?
No field lines pass through it.
A field of flux density 0.20 T passes at right angles through an area of 0.050 m². What is the flux?
0.20 × 0.050.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 6 marks. Write your answers on paper, then check them.
Magnetic flux and flux linkage
Edexcel International A Level Physics WPH · 6 marks · papermunch.org
Name ______________________________ Date ______________
Find the flux through an area of 0.020 m² at right angles to a field of flux density 0.30 T.[2]
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6.0 × 10⁻³ Wb.
A coil of 500 turns has a flux of 2.0 × 10⁻⁵ Wb through each turn. Find the flux linkage.[2]
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0.010 Wb.
A coil in a magnetic field is turned from facing the field squarely to lying edge-on to it. Describe how the flux through it changes.[2]
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It falls from its greatest value, BA, to zero.
Answers: Magnetic flux and flux linkage
- 1. 6.0 × 10⁻³ Wb.
- 2. 0.010 Wb.
- 3. It falls from its greatest value, BA, to zero.