Moving Charges and Magnetism — Class 12 Physics NCERT Solutions (Free)

Free step-by-step NCERT solutions for Class 12 Physics chapter "Moving Charges and Magnetism" — 7 important questions with detailed answers for CBSE board exam preparation.

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TL;DR: Free step-by-step NCERT solutions for Class 12 Physics chapter "Moving Charges and Magnetism" — 7 important questions with detailed answers for CBSE b…

Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated Jul 23, 2026

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Key Questions Covered:

What is magnetic field? State its SI unit and symbol. Write expression for ma…
Define magnetic force on moving charge. An electron moves with velocity 10⁶ m…
What is Hall effect? Explain its significance and write Hall coefficient expr…
Derive expression for magnetic field at center of circular current loop of ra…
What is magnetic dipole? Define magnetic dipole moment and give expression.
A rectangular coil ABCD with sides 10 cm and 5 cm carries current 2 A. It is …
+ 1 more questions in the full chapter

Solutions Summary:

Question	Status
What is magnetic field? State its SI unit and symbol. Wri…	✓ Solved
Define magnetic force on moving charge. An electron moves…	✓ Solved
What is Hall effect? Explain its significance and write H…	✓ Solved
Derive expression for magnetic field at center of circula…	✓ Solved
What is magnetic dipole? Define magnetic dipole moment an…	✓ Solved
A rectangular coil ABCD with sides 10 cm and 5 cm carries…	✓ Solved

Showing 6 of 7 questions

Q1: What is magnetic field? State its SI unit and symbol. Write expression for magnetic field due to long straight current-carrying wire.

Magnetic Field (B): Region around magnet or current-carrying conductor where magnetic force is experienced. SI Unit: Tesla (T) or Weber/m² (Wb/m²) Symbol: B (vector quantity) Smaller unit: Gauss (G) where 1 T = 10⁴ G Magnetic Field due to Long Straight Wire: B = μ₀I/(2πr) where μ₀ = 4π × 10⁻⁷ T⋅m/A (permeability of free space) I = current in wire r = perpendicular distance from wire Direction: Given by right-hand rule - Thumb points in direction of current - Fingers curl in direction of mag...

Q2: Define magnetic force on moving charge. An electron moves with velocity 10⁶ m/s perpendicular to magnetic field of 0.5 T. Calculate force on electron.

Magnetic Force on Moving Charge: Force on charged particle moving in magnetic field. F = qvB sin θ = qv × B (vector form) where q = charge v = velocity B = magnetic field θ = angle between v and B SI Unit: Newton (N) Direction: Given by right-hand rule (for positive charge) - Point fingers in direction of velocity - Curl fingers toward B - Thumb points in direction of force For negative charge, reverse the direction Given: v = 10⁶ m/s B = 0.5 T θ = 90° (perpendicular), sin 90° = 1 q = -e = ...

Q3: What is Hall effect? Explain its significance and write Hall coefficient expression.

Hall Effect: Development of transverse electric field across a conductor carrying current in presence of perpendicular magnetic field. Mechanism: 1. Current flows through conductor due to drift of charge carriers 2. Perpendicular magnetic field exerts force on moving charges 3. Charges accumulate on one side, creating electric field 4. This field creates Hall voltage (V_H) perpendicular to both current and field Hall Voltage: V_H = BR×I/d where R_H = Hall coefficient B = magnetic field I = cu...

Q4: Derive expression for magnetic field at center of circular current loop of radius R.

Consider circular loop of radius R carrying current I. Find field at center O. Take small element dl at distance R from center. Magnetic field due to element dl: dB = (μ₀I dl)/(4π R²) (using Biot-Savart law) Direction of dB: Perpendicular to plane containing dl and position vector (using right-hand rule), pointing outward from loop For circular symmetry, components perpendicular to axis cancel. Only axial component survives. For loop in horizontal plane, vertical component of dB: dB_vertica...

Q5: What is magnetic dipole? Define magnetic dipole moment and give expression.

Magnetic Dipole: Current-carrying loop behaving like a magnet with north and south poles. Magnetic Dipole Moment (m): Measure of strength of magnetic dipole. m = IA where I = current A = area of loop SI Unit: A⋅m² (Ampere-meter squared) Alternatively: J/T (Joule per Tesla) Direction: Perpendicular to plane of loop, given by right-hand rule - Curl fingers in direction of current - Thumb points in direction of m Vector form: m = IA (vector; magnitude IA, direction perpendicular to loop) Pro...

Q6: A rectangular coil ABCD with sides 10 cm and 5 cm carries current 2 A. It is placed in magnetic field 0.5 T perpendicular to plane of coil. Calculate: (a) Magnetic dipole moment (b) Torque if field makes angle 30° with normal to coil

Given: Length L = 10 cm = 0.1 m Breadth B = 5 cm = 0.05 m Current I = 2 A Magnetic field H = 0.5 T (a) Magnetic Dipole Moment: Area A = L × B = 0.1 × 0.05 = 0.005 m² m = IA = 2 × 0.005 = 0.01 A⋅m² Final Answer (a): m = 0.01 A⋅m² or 10 mA⋅m² (b) Torque when field makes 30° with normal: When normal makes 30° with field, the angle between m and B is 30° Torque: τ = mB sin θ = mB sin 30° τ = 0.01 × 0.5 × sin 30° τ = 0.01 × 0.5 × 0.5 τ = 0.0025 N⋅m τ = 2.5 × 10⁻³ N⋅m Final Answer (b): Torque = 2....

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