Class 12 Physics Chapter 6: Electromagnetic Induction (EMI)

the genius April 08, 2026

 

Electromagnetic Induction: Class 12 Physics Chapter 6 Notes in Hindi

Pichle chapters mein humne dekha ki current se magnetism banta hai. Lekin 1831 mein Michael Faraday ne discovers kiya ki iska ulta bhi possible hai. Jab kisi coil se juda magnetic field badalta hai, toh usme current paida hota hai. Isi ko Electromagnetic Induction kehte hain.

1. Magnetic Flux ($\phi_B$)

Kisi surface se perpendicular guzarne waali total magnetic field lines ki sankhya ko Magnetic Flux kehte hain.

  • Formula:

    $$\phi_B = B \cdot A \cos \theta$$

  • Unit: Iski SI unit Weber (Wb) hoti hai.

  • Nature: Ye ek scalar quantity hai.

2. Faraday’s Laws of Induction

Faraday ne do main laws diye:

  1. First Law: Jab bhi kisi circuit se juda magnetic flux change hota hai, toh usme ek Induced EMF paida hota hai.

  2. Second Law: Induced EMF ka magnitude, magnetic flux ke change hone ki rate ke directly proportional hota hai.

    $$\varepsilon = - \frac{d\phi_B}{dt}$$

3. Lenz’s Law

Lenz’s law induced current ki direction batata hai. Iske mutabik, induced current ki direction aisi hoti hai ki wo usi kaaran (cause) ka virodh (oppose) karta hai jisne use paida kiya hai.

  • Significance: Ye Energy Conservation ke law par based hai.

  • Formula mein negative sign ($-$) isi oppose ko dikhata hai.

4. Motional EMF

Jab koi conductor (rod) kisi magnetic field mein move karta hai, toh uske ends par EMF generate hota hai.

$$\varepsilon = Blv$$

(Yahan $B$ = Magnetic field, $l$ = Length of rod, $v$ = Velocity)

5. Eddy Currents (Bhanwar Dharayein)

Jab kisi bulk metal block ko badalte hue magnetic field mein rakha jata hai, toh usme gol-gol chakkar daar current paida hota hai, jise Eddy Currents kehte hain.

  • Uses: Magnetic braking in trains, Induction furnace.

  • Loss: Ye heat ke roop mein energy waste karte hain.

6. Self Induction aur Mutual Induction

FeatureSelf InductionMutual Induction
CoilsSirf ek coil hoti hai.Do coils hoti hain (Primary & Secondary).
ConceptApne hi current change hone se EMF paida karna.Paas wali coil mein current change hone se dusri coil mein EMF paida hona.
Formula$\phi = LI$$\phi_2 = MI_1$
UnitHenry (H)Henry (H)

7. AC Generator

Ye EMI ke principle par kaam karne waali device hai jo Mechanical Energy ko Electrical Energy mein badalti hai.

  • Principle: Jab ek coil magnetic field mein ghumti hai, toh flux change hone se AC current banta hai.

  • EMF Formula:

    $$\varepsilon = NBA \omega \sin(\omega t)$$

8. Top Important Questions (Chapter 6)

Aapke blog readers ke liye ye questions exams mein topper banne mein madad karenge:

Short Questions (1-2 Marks):

  1. Define 1 Henry: Agar current 1 A/s ki rate se change ho aur 1V EMF paida ho, toh inductance 1 Henry hoga.

  2. Lenz’s law energy conservation ko kaise follow karta hai? (Detailed explanation zaroori hai).

  3. Eddy currents ko kam kaise kiya ja sakta hai? Laminated core ka use karke.

Long Questions (3-5 Marks):

  1. State Faraday’s laws of electromagnetic induction.

  2. Derive the expression for Motional EMF ($Blv$).

  3. Explain the working of AC Generator with a neat diagram.

  4. What is Mutual Induction? Derive the expression for two long co-axial solenoids.

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  • Description: Is post mein AC Generator, Faraday's Law aur Self Induction ko asaan Hindi mein samjhaya gaya hai. Diagrams ke saath boards ki taiyari karein.

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