Magnetism

Handle fields due to currents, force on charges, and magnetic-motion geometry with the structured logic JEE uses again and again.

Original Notes2 Core SectionsJEE Revision Style

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JEE Intro

How to Think About Magnetism

Handle fields due to currents, force on charges, and magnetic-motion geometry with the structured logic JEE uses again and again.

This chapter is written as original Learn at My Place teaching copy. The aim is to give you the JEE decision-making layer: what equation to trust, what approximation is valid, and where exam traps usually appear.

Read the full note once, then revisit the quick revision block before solving your own practice questions.

Section A

Notes: Magnetism

Original teaching copy for Learn at My Place

1. Magnetic Field Due to Current and Lorentz Force 2. Conductors and Charged Particle Motion

1. Magnetic Field Due to Current and Lorentz Force

Current produces magnetic field. Around a long straight wire, field lines are concentric circles whose direction is found by the right-hand rule.

A moving charge in magnetic field experiences:

\vec F = q\,\vec v \times \vec B

Magnetic force is perpendicular to velocity, so it changes direction of motion but does no work.

2. Conductors and Charged Particle Motion

A wire of length $L$ carrying current $I$ in magnetic field $B$ feels force:

\vec F = I\,\vec L \times \vec B

If a charged particle enters a uniform magnetic field perpendicularly, it moves in a circle:

r = \frac{mv}{qB}, \qquad T = \frac{2\pi m}{qB}

If velocity has a component along the field as well, the path becomes helical.

Quick Revision

Last 5-Minute Recall

JEE exam rule: First identify the governing principle. Most errors happen because students choose the wrong framework before they start the algebra.

Magnetic field and right-hand-rule orientation

Force on a moving charge

Force on a current-carrying conductor

Motion of charged particles in uniform magnetic field

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