Science · Class 12
Magnetic Effects of Current
Learn Magnetic Effects of Current with notes, examples, and practice questions.
3 sections15–25 min read6 MCQs · 2 examples
Chapter Overview
Moving charges and currents create magnetic fields. Biot-Savart and Ampere's laws give B fields; forces on charges and currents follow Lorentz force.
Field & Force
Lorentz force
F⃗ = q(v⃗×B⃗) ; F = BIL sin θ (wire)
Long straight wire
B = μ₀I/(2πr)
Solenoid
B = μ₀nI (interior)
Circular loop centre
B = μ₀I/(2R)
Moving Coil Galvanometer
- Torque τ = NIAB sin θ
- Converted to ammeter (shunt) or voltmeter (series R)
- Current sensitivity vs voltage sensitivity
Solved Examples
Step-by-step solutions — read each step before checking the final answer.
Force on wire
I=2A, L=0.5m, B=0.4T, perpendicular.
- 1F=BIL=0.4N
Answer
0.4 N
Field at distance
Wire I=10A, r=0.05m.
- 1B=μ₀I/(2πr)≈4×10⁻⁵ T
Answer
≈ 4×10⁻⁵ T
Key Points to Remember
- ✓ Right-hand rule for direction
- ✓ Parallel currents attract if same direction
- ✓ Earth's field ~10⁻⁵ T
Exam Tips
- • Use Fleming's left-hand rule for force
- • Draw field patterns for loops and solenoids
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Formula Cheat Sheet
Quick reference — NCERT board exam formulas
Magnetic Field & Force
- Lorentz force:F⃗ = q(v⃗×B⃗)
- Force on wire:F = BIL sin θ
- Long straight wire:B = μ₀I/(2πr)
- Solenoid:B = μ₀nI (interior)
- Circular loop (centre):B = μ₀I/(2R)
- Galvanometer torque:τ = NIAB sin θ
Practice MCQs — Magnetic Effects of Current
Test your understanding with topic-wise multiple choice questions. Explanations appear after each answer.
Question 1 of 6Score: 0/0
Unit of magnetic field B: