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Faraday’s Law is one of the most important concepts in electricity and magnetism, especially for Class 10–12 students. It explains how electricity can be generated using magnetism.
But here’s the real challenge: most students memorize the formula but struggle to visualize what is actually happening.
Whenever there is a change in magnetic field linked with a conductor, an emf (voltage) is induced in it.
The Core Formula: E = - dΦ/dt
Important: It’s not the magnetic field itself, but how fast it changes that matters.
Magnetic flux is the amount of magnetic field passing through a surface.
Visualization Table: Magnetic Flux
| Situation | Magnetic Flux |
|---|---|
| Strong magnetic field | High flux |
| Weak magnetic field | Low flux |
| Larger area | More flux |
| Tilted surface | Less flux |
1. Moving Magnet and Coil
Magnet moves -> Magnetic field changes -> Current flows
Magnet stops -> No current
| Action | Result |
|---|---|
| Magnet moving toward coil | Current induced |
| Magnet moving away | Current induced (opposite direction) |
| Magnet stationary | No current |
2. Changing Area of Loop
If loop size changes, flux changes -> current is produced.
3. Rotating Coil
Used in generators. Rotation changes angle -> flux changes -> electricity generated.
Magnetic Flux Formula: Φ = B A cosθ
| Factor | How It Changes Flux |
|---|---|
| Magnetic field (B) | Increase/decrease field strength |
| Area (A) | Expand or shrink loop |
| Angle (θ) | Rotate the loop |
| Device | What Changes? | Result |
|---|---|---|
| Generator | Rotation | Electricity |
| Transformer | Current variation | Voltage change |
| Dynamo | Motion | Light |
The induced current always opposes the change causing it.
| Wrong Thinking | Correct Thinking |
|---|---|
| Magnetic field creates current | Change in flux creates current |
| Strong magnet always gives current | Only if flux changes |
| Memorize formula | Understand concept |
Change in flux = 0.6 − 0.2 = 0.4 Wb
Time = 0.2 s
Emf = 0.4 / 0.2 = 2V
| Concept | Key Idea |
|---|---|
| Faraday’s Law | Change in flux → emf |
| Magnetic Flux | Field through area |
| Lenz’s Law | Opposes change |
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