Edexcel A Level (IAL) Physics-4.28 Induced E.M.F in a Moving Coil- Study Notes- New Syllabus

Factors Affecting the e.m.f. Induced in a Coil

When there is relative motion between a coil and a permanent magnet, an e.m.f. is induced in the coil. This phenomenon is explained by Faraday’s law of electromagnetic induction.

Faraday’s Law of Electromagnetic Induction

The magnitude of the induced e.m.f. is proportional to the rate of change of magnetic flux linkage:

\( \varepsilon = \dfrac{\Delta (N\phi)}{\Delta t} \)

• \( \varepsilon \) = induced e.m.f. (V)
• \( N \) = number of turns in the coil
• \( \phi \) = magnetic flux through one turn (Wb)

Key idea: An induced e.m.f. is produced only when the magnetic flux linkage changes.

Relative Motion Between Coil and Magnet

• Moving the magnet towards or away from the coil changes the magnetic flux through the coil.
• Moving the coil instead of the magnet has the same effect.
• It is the relative motion that matters.

Factors Affecting the Magnitude of the Induced e.m.f.

(a) Speed of Motion

• Faster motion produces a greater rate of change of flux.
• Greater rate of change of flux linkage gives a larger induced e.m.f.
• Doubling the speed approximately doubles the induced e.m.f.

(b) Strength of the Magnetic Field

• A stronger magnet produces a larger magnetic flux.
• For the same motion, the change in flux is greater.
• This increases the induced e.m.f.

(c) Number of Turns in the Coil

• Flux linkage is given by \( N\phi \).
• Increasing the number of turns increases the total flux linkage.
• This increases the induced e.m.f.

(d) Area of the Coil

• Magnetic flux depends on the area of the coil.
• Larger area intercepts more magnetic field lines.
• This increases the change in flux and hence the induced e.m.f.

(e) Orientation of the Coil

• Flux depends on the angle between the magnetic field and the coil.
• Maximum flux occurs when the field is perpendicular to the plane of the coil.
• Changing orientation during motion changes the flux linkage.

Direction of the Induced e.m.f.

• The direction depends on whether flux is increasing or decreasing.
• Lenz’s law determines the direction (opposes the change in flux).