Physics
Mechanics Thermodynamics Optics Electrostatics & Current Magnetism & EMI Modern Physics
Module 1 · JEE Physics

Magnetism & EMI

Magnetic effects, Biot-Savart, Ampere's law, EMI, AC circuits, electromagnetic waves.
Magnetic Effects · EMI · AC Circuits · EM Waves
🎯 Take Mock Test

Learning Objectives

  • Understand the fundamental concepts of Magnetism & EMI
  • Apply key formulas and techniques to solve problems
  • Practice with exam-level questions to build speed and accuracy

Key Concepts

What is Magnetism?

Magnetism deals with magnetic fields, their sources, and their effects on moving charges and magnetic materials. For NEET, key topics include Biot-Savart law, Ampere's circuital law, force on a current-carrying conductor, magnetic moment, Earth's magnetism, and electromagnetic induction. This topic bridges electricity and magnetism, forming the basis of electromagnetism.

Key Concepts

Biot-Savart Law: dB = (μ0/4π)(Idl × r)/r3. Magnetic field due to straight conductor: B = (μ0I)/(2πr). Force on a moving charge: F = q(v × B). Force on a current-carrying conductor: F = I(L × B). Ampere's Law: &oblique8;B·dl = μ0Ienc. Magnetic moment: M = IA for a current loop. Faraday's Law: Induced emf ε = -dΦB/dt. Lenz's Law: Induced current opposes the change causing it.

Solved Examples

Example 1
A long straight wire carries a current of 5 A. Find the magnetic field at a distance of 2 cm from the wire. (μ0 = 4π × 10-7 Tm/A)

a) 5 × 10-5 T b) 2.5 × 10-5 T c) 1 × 10-4 T d) 4 × 10-5 T
Solution: B = (μ0I)/(2πr) = (4π × 10-7 × 5)/(2π × 0.02) = (20π × 10-7)/(0.04π) = (20 × 10-7)/(0.04) = 5 × 10-5 T. Hence option (a) is correct.
Example 2
A proton enters a magnetic field of 0.2 T with a velocity of 106 m/s perpendicular to the field. Find the radius of its circular path. (mp = 1.67 × 10-27 kg, q = 1.6 × 10-19 C)

a) 2.6 cm b) 5.2 cm c) 1.3 cm d) 10.4 cm
Solution: For circular motion in magnetic field, qvB = mv2/r. r = mv/(qB) = (1.67 × 10-27 × 106)/(1.6 × 10-19 × 0.2) = (1.67 × 10-21)/(3.2 × 10-20) = 0.052 m = 5.2 cm. Hence option (b) is correct.
Example 3
A circular coil of radius 5 cm has 100 turns and carries a current of 2 A. Find the magnetic field at its center.

a) 8π × 10-4 T b) 4π × 10-4 T c) 2π × 10-3 T d) 8π × 10-3 T
Solution: B at center of circular coil = (μ0NI)/(2r) = (4π × 10-7 × 100 × 2)/(2 × 0.05) = (8π × 10-5)/(0.1) = 8π × 10-4 T. Hence option (a) is correct.

Shortcut Techniques

  • For magnetic field direction, use the right-hand thumb rule: thumb points in direction of current, fingers curl in direction of magnetic field.
  • For force between two parallel current-carrying wires, currents in same direction attract, opposite directions repel.
  • In electromagnetic induction, the induced emf is maximum when the coil rotates perpendicular to the magnetic field.
  • For a solenoid, B = μ0nI, where n is number of turns per unit length.
Pro Tip
For NEET, learn Fleming's left-hand rule (for force on current-carrying conductor) and right-hand rule (for induced current in generators). These mnemonics save time in the exam and reduce sign errors.

Application-Based Learning

Connect concepts to real-world applications: Why sky is blue (Rayleigh scattering), how pressure cookers work, why apples turn brown (oxidation).

Problem-Solving Methodology

1) Identify given data. 2) Recall formulas. 3) Check unit consistency. 4) Solve step-by-step. 5) Verify through estimation.

Pro Tip
Check if your answer is reasonable through order-of-magnitude estimation to catch gross errors.

Application-Based Learning

Connect concepts to real-world applications: Why sky is blue (Rayleigh scattering), how pressure cookers work, why apples turn brown (oxidation).

Problem-Solving Methodology

1) Identify given data. 2) Recall formulas. 3) Check unit consistency. 4) Solve step-by-step. 5) Verify through estimation.

Pro Tip
Check if your answer is reasonable through order-of-magnitude estimation to catch gross errors.

Application-Based Learning

Connect concepts to real-world applications: Why sky is blue (Rayleigh scattering), how pressure cookers work, why apples turn brown (oxidation).

Problem-Solving Methodology

1) Identify given data. 2) Recall formulas. 3) Check unit consistency. 4) Solve step-by-step. 5) Verify through estimation.

Pro Tip
Check if your answer is reasonable through order-of-magnitude estimation to catch gross errors.

Application-Based Learning

Connect concepts to real-world applications: Why sky is blue (Rayleigh scattering), how pressure cookers work, why apples turn brown (oxidation).

Problem-Solving Methodology

1) Identify given data. 2) Recall formulas. 3) Check unit consistency. 4) Solve step-by-step. 5) Verify through estimation.

Pro Tip
Check if your answer is reasonable through order-of-magnitude estimation to catch gross errors.

Practice Questions

← Electrostatics & Current Modern Physics →