⚡ Electromagnetic Induction — Class 12 Physics Notes

Chapter Introduction

Electromagnetic Induction — Class 12 Physics Notes| Masternotes.in

Electromagnetic Induction Class 12 Notes PDF — Faraday’s Law,Lenz’s Law, Lenz’s Law, Eddy Currents, Motional EMF aur AC Generator — NCERT aur HBSE board ke liye free handwritten notes. Easy language mein samjho aur PDF download karo —MasterNotes.in

Socho ek simple sawaal — bijli kaise banti hai?
Ghar mein jo bijli aati hai, factory mein jo machines chalti hain, train jo chalti hai — sab ke peeche ek hi concept hai: Electromagnetic Induction.
Yeh concept Michael Faraday ne 1831 mein discover kiya tha. Unhone dekha ki jab ek magnet ko coil ke paas laate hain ya door le jaate hain, toh coil mein current flow karne lagta hai — bina kisi battery ke!
Yahi hai Electromagnetic Induction — magnetic field ke change se electric current produce karna.on.

🔑 Key Terms — Pehle Samjho

1. Magnetic Flux (Φ)

Magnetic flux matlab — kitni magnetic field lines ek surface se guzar rahi hain.

Formula:

Φ = B × A × cos θ

Jahan:

• B = Magnetic field (Tesla mein)
• A = Surface ka area (m² mein)
• θ = B aur surface ke normal ke beech ka angle

Easy example: Socho ek jali (net) hai. Jitni zyada hawa us jali se guzregi, utna zyada “flux” hoga. Agar hawa seedhi aaye — flux maximum. Agar hawa parallel aaye — flux zero.

Unit: Weber (Wb) ya Tesla·m²

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📜 Faraday’s Laws of Electromagnetic Induction

First Law:

“Jab bhi kisi coil se guzarne wala magnetic flux change hota hai, tab us coil mein ek EMF (electromotive force) induce hoti hai.”

Matlab — flux change hoga tabhi current produce hogi. Flux stable raha toh kuch nahi hoga.

Second Law:

“Induce hone wali EMF ki value, flux ke change hone ki rate ke barabar hoti hai.”

Formula:

EMF (ε) = −ΔΦ/Δt

Yahan minus sign hai — kyun? Yeh humein Lenz’s Law ki taraf le jaata hai.

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🔄 Lenz’s Law — Ek Simple Samajh

Lenz’s Law kehta hai: Induce hone wali current ki direction hamesha aisi hogi jo us flux change ka virodh (oppose) kare jis se woh paida hui hai. Electromagnetic Induction — Class 12 Physics Notes

Easy example:

• Magnet ka North pole coil ki taraf aane do
• Flux badh raha hai
• Coil mein current aise direction mein flow karegi ki woh ek North pole bana le apni taraf — taaki magnet ko rok sake
• Yeh energy conservation ka natural niyam hai

Yaad rakhne ka trick: Lenz’s Law = Nature hamesha change ka virodh karti hai.

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🔧 Motional EMF

Jab ek conductor (wire) magnetic field mein move karta hai, toh us mein EMF induce hoti hai. Ise Motional EMF kehte hain.

Formula:

ε = Blv

Jahan:

• B = Magnetic field
• l = Conductor ki length
• v = Conductor ki velocity

Example: Ek rod hai jo rails pe slide kar rahi hai, magnetic field mein. Rod move karegi toh current flow karegi — yahi principle generators mein use hoti hai!

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⚙️ Eddy Currents (Bhrawar Dhaara)

Jab ek solid metal ko changing magnetic field mein rakha jaaye, toh us metal ke andar bhi currents flow karne lagti hain — yeh circular paths mein hoti hain jaise paani mein bhrawar (whirlpool). Electromagnetic Induction — Class 12 Physics Notes

Inhe Eddy Currents kehte hain.

Eddy Currents ke Nuksan:

• Energy heat ke roop mein waste hoti hai
• Motors, transformers mein loss hota hai

Eddy Currents Ko Kam Kaise Karte Hain:

Lamination — metal ko ek solid piece ki jagah patli-patli sheets mein banate hain. Inke beech insulation hoti hai jo eddy currents ko rok deti hai.

Eddy Currents Ke Fayde (Uses):

• Induction Cooker — Eddy currents se hi bartan garam hota hai
• Magnetic Braking — Train aur roller coasters mein smooth braking ke liye
• Metal Detector — Airport pe jo machine hoti hai — eddy currents se hi kaam karti hai
• Electric Meter — Bijli meter mein eddy currents se disc ghoomti hai

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🌀 Self Induction — Khud Se EMF Banana

Jab kisi coil mein current flow karta hai, toh woh apne aas-paas ek magnetic field banata hai. Jab yeh current change hota hai, toh magnetic field bhi change hoti hai — aur is change se usi coil mein ek EMF induce hoti hai. Electromagnetic Induction — Class 12 Physics Notes

Ise Self Induction kehte hain.

Formula:

ε = −L × dI/dt

Jahan L = Self Inductance (unit: Henry — H)

Self Inductance Kab Zyada Hogi:

• Coil mein zyada turns (N) ho
• Coil ka area zyada ho
• Andar iron core ho

Example: Jab bulb wali circuit mein coil lagao aur switch off karo — bulb ek baar aur chamkta hai. Kyun? Kyunki coil stored energy release karti hai self induction se! (faraday’s law of electromagnetic induction class 12)

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🔁 Mutual Induction — Dono Coils Ka Khel

Jab do coils ek doosre ke paas hoon aur ek mein current change ho, toh doosri coil mein EMF induce hoti hai — yeh Mutual Induction hai.

Formula:

ε₂ = −M × dI₁/dt

Jahan M = Mutual Inductance (unit: Henry)

Yahi principle hai Transformer ka!

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🔃 AC Generator — Bijli Kaise Banti Hai

AC Generator electromagnetic induction ka sabse important practical use hai.

Parts:

• Armature — Wire ki rectangular coil
• Magnet — Strong permanent ya electromagnet
• Slip Rings — Current bahar nikalne ke liye
• Brushes — Slip rings se contact karte hain

Kaam Kaise Karta Hai:

1. Coil ko magnetic field mein rotate karte hain
2. Rotate hone se flux continuously change hota hai
3. Flux change se EMF induce hoti hai Electromagnetic Induction — Class 12 Physics Notes
4. Yeh EMF continuously direction badlti hai — isliye Alternating Current (AC) milta hai

Formula:

ε = NBA ω sin(ωt) ε = ε₀ sin(ωt)

Jahan ε₀ = Peak EMF = NBAω

Important Points:

• Jab coil plane magnetic field ke parallel ho → EMF maximum hoti hai
• Jab coil plane magnetic field ke perpendicular ho → EMF zero hoti hai

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📊 Important Formulas — Ek Jagah

Formula	Kya Hai
Φ = BAcosθ	Magnetic Flux
ε = −ΔΦ/Δt	Faraday’s Law
ε = Blv	Motional EMF
ε = −L dI/dt	Self Induction EMF
ε = −M dI₁/dt	Mutual Induction EMF
ε₀ = NBAω	Peak EMF in Generator

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💡 Daily Life Mein Electromagnetic Induction:- Electromagnetic Induction — Class 12 Physics Notes

Jagah	Kaise Use Hota Hai
Power Station	Generator se AC current
Transformer	Mutual Induction se voltage change
Induction Cooker	Eddy currents se heating
Metal Detector	Eddy currents se detection
Credit Card	Magnetic strip mein induction
Wireless Charging	Mutual induction se phone charge
Electric Guitar	String ki vibration se induction

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❓ Exam Mein Pooche Jaane Wale Important Questions

1 Mark:

• Lenz’s Law kya hai?
• Eddy currents ke 2 uses likhо
• Self inductance ki unit kya hai?

2 Mark:

• Faraday ke dono laws explain karo
• Motional EMF ka formula derive karo
• Mutual inductance aur self inductance mein antar

3-5 Mark:

• AC Generator ka diagram aur working explain karo
• Eddy currents kya hain — fayde aur nuksan dono likhо
• Lenz’s Law ko energy conservation se kaise relate karein — explain karo

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🧠 Quick Revision — 2 Minute Mein

• Flux change → EMF induce hoti hai ✅
• Lenz’s Law → Change ka virodh ✅
• Motional EMF → ε = Blv ✅
• Self Induction → Apni coil mein EMF ✅
• Mutual Induction → Doosri coil mein EMF ✅
• Eddy Currents → Solid metal mein circular currents ✅
• AC Generator → Rotation se AC current ✅

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About Author

Name – Ankita

Teacher Name – Dinesh Kumar

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1.	Electric Charges and Fields	Click
2.	Electrostatic Potential and Capacitance	Click
3.	Current Electricity	Click
4.	Moving Charges and Magnetism	Click
5.	Magnetism and Matter	Click
6.	Electromagnetic Induction	Click
7.	Alternating Current	Click
8.	Electromagnetic Waves	Click
9.	Ray Optics and Optical Instruments	Click
10.	Wave Optics	Click
11.	Dual Nature of Radiation and Matter	Click
12.	Atoms	Click
13.	Nuclei	Click
14.	Semiconductor Electronics	Click
15.	Communication Systems	Click
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