Class 12 Physics Chapter 3: Current Electricity

the genius April 08, 2026

 

Current Electricity: Class 12 Physics Chapter 3 Notes in Hindi

Pichle do chapters mein humne ruka hua charge (Static Electricity) padha tha, lekin is chapter mein hum Behte hue charge (Flowing Charges) yaani Current ke baare mein vistar se jaanenge.

1. Electric Current (Vidyut Dhara)

Kisi conductor ke cross-section se per unit time mein flow hone waale net charge ko Electric Current kehte hain.

  • Formula:

    $$I = \frac{q}{t}$$

  • Unit: Iski SI unit Ampere (A) hai.

  • Direction: Current ki direction hamesha positive charge ke flow ki taraf aur electrons ke flow ke opposite hoti hai.

2. Drift Velocity ($v_d$)

Jab kisi conductor par electric field apply kiya jata hai, toh electrons ek average velocity ke saath positive terminal ki taraf badhte hain. Is average velocity ko Drift Velocity kehte hain.

  • Relation between I and $v_d$:

    $$I = nAev_d$$

    (Yahan $n$ = electron density, $A$ = area, $e$ = charge of electron)

3. Ohm’s Law

Physical conditions (jaise temperature) constant rehne par, conductor ke across potential difference ($V$), usme behne waale current ($I$) ke directly proportional hota hai.

$$V = IR$$

Yahan $R$ (Resistance) hai, jiski unit Ohm ($\Omega$) hoti hai.

4. Resistance aur Resistivity

  • Resistance ($R$): Ye current ke raaste mein aane waali rukawat hai. Ye length ($l$) ke proportional aur area ($A$) ke inversely proportional hota hai.

    $$R = \rho \frac{l}{A}$$

  • Resistivity ($\rho$): Ye material ki property hai. Ye temperature badhne par badhti hai (conductors ke liye).

5. Kirchhoff’s Laws (Most Important for Numericals)

Complex circuits ko solve karne ke liye Kirchhoff ne do laws diye:

  1. Junction Law (KCL): Kisi junction par aane waale currents ka sum, wahan se jaane waale currents ke sum ke barabar hota hai. (Charge conservation par based hai).

  2. Loop Law (KVL): Ek closed loop mein total potential difference ka sum zero hota hai. (Energy conservation par based hai).

    3. Shutterstock

6. Wheatstone Bridge

Ye char resistors ka ek aisa arrangement hai jisse hum kisi unknown resistance ki value nikal sakte hain.

  • Balanced Condition:

    $$\frac{P}{Q} = \frac{R}{S}$$

7. Top Important Questions (Chapter 3)

Aapne blog post mein ye questions zaroor shamil karein kyunki students inhe dhoondhte hain:

Short Questions:

  1. Mobility kya hai? Unit drift velocity per unit electric field ko mobility ($\mu$) kehte hain.

  2. Temperature ka resistance par kya asar padta hai? Conductors ka resistance badhta hai, jabki semiconductors ka kam hota hai.

  3. Internal Resistance kya hai? Cell ke andar ke electrolyte jo rukawat paida karte hain use internal resistance ($r$) kehte hain.

Long Derivations:

  1. Derive the relation between Drift Velocity and Current.

  2. Explain Wheatstone Bridge with a neat diagram.

  3. Comparison of EMF of two cells using Potentiometer.

  4. Cells in Series and Parallel: Iska equivalent EMF aur internal resistance nikalna.

Conclusion

Current Electricity chapter na sirf exams ke liye balki daily life ki physics samajhne ke liye bhi zaroori hai. Ohm's law aur Kirchhoff's law par pakad banayein, aapke marks pakke hain!

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