Current Electricity
Learn Current Electricity with notes, examples, and practice questions.
Chapter Overview
Current electricity deals with flow of charge in conductors — drift velocity, Ohm's law, resistance networks, and electrical power.
Core Relations
Current
I = Q/t = nAve_d
Ohm's law
V = IR
Resistance
R = ρL/A
Resistivity
ρ depends on material and temperature
Power
P = VI = I²R = V²/R
Circuits
Series
R_eq = R₁+R₂; same I
Parallel
1/R_eq = 1/R₁+1/R₂; same V
Kirchhoff
ΣI at junction = 0; ΣV in loop = 0
Wheatstone bridge
Balanced when P/Q = R/S
Cells
- EMF ε: terminal voltage with no current
- Internal resistance r: V = ε − Ir
- Cells in series: ε add; parallel: same ε
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Ohm's law
R=10Ω, V=5V. Find I.
- 1I=V/R=0.5A
Answer
0.5 A
Power
100W bulb at 220V.
- 1I=P/V≈0.45A
- 2R=V²/P≈484Ω
Answer
≈0.45 A, R≈484Ω
Key Points to Remember
- ✓ Conventional current: + to −
- ✓ Potentiometer measures EMF accurately
- ✓ Colour code for resistors
Exam Tips
- • Draw circuit diagram
- • Apply Kirchhoff for complex circuits
- • Check series vs parallel
Formula Cheat Sheet
Quick reference — NCERT board exam formulas
Current & Resistance
- Current:I = Q/t = nAve_d
- Ohm's law:V = IR
- Resistance:R = ρL/A
- Power:P = VI = I²R = V²/R
Circuits & Cells
- Series:R_eq = R₁+R₂ ; same I
- Parallel:1/R_eq = 1/R₁+1/R₂ ; same V
- Kirchhoff:ΣI at junction = 0 ; ΣV in loop = 0
- Wheatstone bridge:Balanced when P/Q = R/S
- Cell:V = ε − Ir
Practice MCQs — Current Electricity
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Ohm's law: V =