⚡ ELECTROMAGNETIC INDUCTION · EMI
Faraday's law • Lenz's law • Motional EMF • Self & Mutual inductance • AC generator • Eddy currents • NEET problems
🧲 MAGNETIC FLUX & FARADAY'S LAW
Magnetic flux: ΦB = ∫ B·dA = B A cosθ (for uniform B). Unit: Weber (Wb).
Faraday's law: Induced EMF = – dΦ/dt
For N turns: ε = – N dΦ/dt
If Φ = NBA cosθ and θ varies (rotation): ε = NBA ω sin(ωt) (AC generator).
📐 Magnetic flux through a loop
🔄 LENZ'S LAW (Direction of Induced EMF)
The induced current opposes the change in magnetic flux that produced it.
Lenz's law = conservation of energy.
🖍️ Lenz's law demonstration (magnet falling through coil)
🏃 MOTIONAL EMF
When a conductor moves in a magnetic field, an EMF is induced.
For a rod moving perpendicular to B: ε = Bℓv
Direction: Fleming's right‑hand rule (thumb = motion, index = field, middle = current).
Rotating rod in B: ε = ½ B ω ℓ²
Sliding bar on rails: ε = Bℓv, current = Bℓv/R, power = (Bℓv)²/R.
📏 Motional EMF in a moving rod
🔋 SELF INDUCTION & INDUCTANCE (L)
EMF induced in a coil due to change in its own current: ε = – L (dI/dt).
Self inductance: L = NΦ/I = μ₀ n² A ℓ (solenoid). Unit: Henry (H).
Energy stored in inductor: U = ½ L I²
Inductors oppose sudden changes in current (back EMF).
🔧 Symbol for inductor & growth/decay of current in LR circuit
🔄 MUTUAL INDUCTION
EMF induced in a coil due to changing current in a nearby coil: ε₂ = – M dI₁/dt.
Mutual inductance M depends on geometry, number of turns, and medium.
For two coaxial solenoids: M = μ₀ n₁ n₂ A ℓ.
⚡ AC GENERATOR
Converts mechanical energy to electrical energy. Rotating coil in uniform B induces sinusoidal EMF.
Instantaneous EMF: ε = NBA ω sin(ωt).
Peak EMF: ε₀ = NBA ω. Frequency: f = ω/(2π).
🔄 AC generator principle
🌀 EDDY CURRENTS
Induced circulating currents in bulk conductors when subjected to changing magnetic flux.
Applications: Induction furnaces (heating), electromagnetic braking, damping in galvanometers.
Reduction: Laminating cores (thin insulated sheets) increases resistance, reduces eddy currents.
💡 NEET TIPS & SHORTCUTS
- Induced EMF depends on rate of change of flux, not flux itself.
- For a coil rotating in B, ε = NBAω sin(ωt); average EMF over half cycle = 2NBAω/π.
- In LR circuit, current grows as I = (V/R)(1 – e–Rt/L) and decays as I = I₀ e–Rt/L.
- Mutual inductance M = √(L₁L₂) for perfect coupling.
⚠️ COMMON MISTAKES
- Forgetting negative sign in Faraday's law (Lenz's law).
- Using wrong sign for induced EMF in loops.
- Confusing self‑inductance with mutual inductance.
- Assuming eddy currents are always undesirable – they have practical uses.
📌 QUICK REVISION CARD
Magnetic flux: Φ = B·A = BA cosθ
Faraday's law: ε = – dΦ/dt
Motional EMF: ε = Bℓv
Self inductance (solenoid): L = μ₀ n² A ℓ
Energy in inductor: U = ½ L I²
AC generator: ε = NBA ω sin(ωt)
LR time constant: τ = L/R
Mutual inductance: M = k √(L₁L₂)
⚡ ELECTROMAGNETIC INDUCTION • NEET REVISION NOTES
📸 NOTES PREVIEW
Preview of Electromagnetic Induction Notes
📥 DOWNLOAD ELECTROMAGNETIC INDUCTION NOTES PDF
Download Electromagnetic Induction Revision Notes for NEET Physics PDF for quick revision and strong conceptual clarity. This chapter is one of the most important topics in Electrodynamics and is frequently asked in NEET.
These Electromagnetic Induction handwritten notes PDF free download include Faraday’s laws, Lenz’s law, magnetic flux, induced EMF, self inductance, mutual inductance, and all important formulas, tricks, and PYQ-based concepts.
- Concept-based + numerical questions in NEET
- Faraday’s Law and Lenz’s Law are frequently asked
- Foundation for Alternating Current chapter
- Flux and inductance concepts are very important
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📊 WEIGHTAGE ANALYSIS
1–2 Questions
Faraday + Lenz + flux
High Weightage
Theory + numericals
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