Magnetic Effect of Electric Current Class 12 - IIT JEE | NEET

When electric current flows through a wire, it generates a magnetic field around the wire. This is called the magnetic effect of electric current. The strength of the field depends on the magnitude of the current and the distance from the wire. This was first discovered by Oersted in 1820 and forms the foundation of Chapter 4 in Class 12 Physics.

This chapter (Moving Charges and Magnetism) typically carries 8–12 marks in JEE Main across the paper and 4–8 marks in NEET, based on previous year trends. In CBSE board exams, the combined unit of Magnetic Effects of Current and Magnetism carries 16 marks. Regular practice of PYQs from this chapter gives a strong return on study time.

Biot-Savart Law calculates the magnetic field due to a small current element and works for any geometry, including finite wires and circular arcs. Ampere's Circuital Law uses a closed loop integral and works best when there is high symmetry — like infinite wires, solenoids, and toroids. For irregular or finite-length conductors, Biot-Savart is the correct approach.

NCERT is sufficient to answer approximately 65–70% of NEET questions from this chapter. Focus on all in-text examples, NCERT exercises, and the diagrams for galvanometer and solenoid. For full marks, supplement NCERT with previous year NEET questions and eSaral's topic-wise tests to cover the remaining conceptual variations.

The radius of circular motion of a charged particle in a uniform magnetic field is r = mv / qB, where m is mass, v is velocity, q is charge, and B is magnetic field strength. The time period T = 2πm/qB is independent of velocity, which is a frequently tested MCQ fact in both JEE Main and NEET.