Cambridge A Levels A2 Physics Chapter 20 Magnetic Fields Part 1
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Module
Cambridge A Levels A2 Physics
Institution
Chapter 20 Magnetic Fields Part 3: 20 pages
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20.4 Electromagnetic Induction
Magnetic Flux and Magnetic Flux Linkage
Magnetic Flux,
The product of the magnetic flux density and the area normal to the lines of flux.
Magnetic Flux
Unit of : weber (Wb) / Tm-2
𝜙 = 𝐵𝐴
B: magnetic flux density (perpendicular to the area)
A: cross-sectional area
One weber (1 Wb) is the magnetic flux that passes perpendicular through a cross-section of area 1 m2
when the magnetic flux density is 1 T.
Magnetic Flux Density, B Magnetic Flux,
The no. of magnetic field lines passing The total no. of magnetic field lines
through a region per unit area. passing through a cross sectional area, A
The angle between the magnetic field and the normal to the area affects .
When the field lines is parallel to the plane When the field lines is perpendicular to the
of area, plane of area,
through A = 0 through A = maximum
, B cos
The component of magnetic flux
density, B perpendicular to the plane
of the cross-sectional area
= (B cos)A
= BAcos
𝜙 = 𝐵𝐴 𝑐𝑜𝑠 𝜃
: the angle between the normal to the area and the magnetic field
When = 90o, = 0. When = 0o, = BA.
Magnetic Flux Linkage
For a coil with N turns, the magnetic flux linkage is defined as the product of the magnetic flux and the
number of turns.
, An e.m.f is induced in a circuit whenever magnetic flux linking the circuit changes with respect to time.
Ways an e.m.f can be induced:
𝜙 = 𝐵𝐴 𝑐𝑜𝑠 𝜃
1) Changing the magnetic flux density, B
2) Changing the cross-sectional area of the circuit, A
3) Changing the angle,
Electromagnetic Induction
Electromagnetic Induction
The process in which an e.m.f is induced in a closed circuit due to changes in magnetic flux.
Electromagnetic induction occurs when:
▪ A conductor cuts through a magnetic field.
▪ The direction of a magnetic field through a coil changes.
When the conductor cuts through the magnetic field lines:
1) This causes a change in magnetic flux.
2) Which causes work to be done.
3) The work is then transformed into electrical energy.
4) An e.m.f is induced in the closed circuit of the conductor.
Electromagnetic Induction is used in:
▪ Electrical geenrators
▪ Transformers
Current Direction in Electromagnetic Induction
The direction of the induced e.m.f / current in a wire moving through a magnetic field at right angles to the
field can be determined using Fleming’s Right-Hand Rule.
Fleming’s Right Hand Rule:
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