What is Electromagnetic Induction?
Electromagnetic induction is the process by which a changing magnetic field creates an electric current in a nearby conductor. It's the principle behind generators, transformers and induction charging.
Electromagnetic induction produces an EMF whenever magnetic flux through a coil changes: ε = N·(ΔΦ/Δt), known as Faraday's law of induction.
- 1↓Magnet at restNo relative motion, no flux change, no EMF induced.
- 2↓Magnet moves toward coilMagnetic flux through the coil increases with time.
- 3↓Faraday's law appliesChanging flux induces an EMF: ε = N·(ΔΦ/Δt).
- 4Lenz's law sets directionInduced current flows to oppose the flux change, creating a repelling field.
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Step-by-step worked examples
A 100-turn coil experiences a flux change from 0.02 Wb to 0.05 Wb in 0.5 s. Find the induced EMF.
ΔΦ = 0.05 − 0.02 = 0.03 Wb ε = N × ΔΦ/Δt ε = 100 × 0.03/0.5 = 6 V
A single loop (N = 1) has a flux change of 0.01 Wb in 0.1 s. Find the induced EMF.
ε = N × ΔΦ/Δt ε = 1 × 0.01/0.1 = 0.1 V
A 200-turn coil produces an EMF of 12 V over 0.2 s. Find the flux change.
ε = N × ΔΦ/Δt → ΔΦ = ε×Δt/N ΔΦ = 12 × 0.2/200 ΔΦ = 0.012 Wb
Flashcards
Quick quiz
Q1.What does Faraday's law state?
Q2.What does Lenz's law describe?
Q3.A coil with more turns, all else equal, produces…
Q4.Which device works directly on electromagnetic induction?
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Common mistakes
Thinking any magnetic field near a coil induces a current. — Correct: Only a changing flux induces an EMF — a static field does nothing.
Ignoring the number of turns N in calculations. — Correct: EMF scales directly with N; forgetting it underestimates the result.
Confusing Faraday's law (magnitude) with Lenz's law (direction). — Correct: Faraday's law gives how much EMF; Lenz's law gives which way current flows.
Assuming flux and field strength are the same thing. — Correct: Flux Φ = B×A×cosθ depends on field, area and angle — not just field strength.
FAQ
What is electromagnetic induction?
It's the generation of an EMF in a conductor caused by a changing magnetic flux, described by Faraday's law.
What is the formula for electromagnetic induction?
ε = N × (ΔΦ/Δt), where N is the number of turns and ΔΦ/Δt is the rate of flux change.
What are examples of electromagnetic induction?
Electric generators, transformers, induction cooktops and wireless charging pads.
How do you calculate the EMF from electromagnetic induction?
Multiply the number of coil turns by the rate of change of magnetic flux: ε = N·ΔΦ/Δt.