Magnetic Effects & Magnetism

JEE Main level, single correct, medium

42 of 276

Question 42 of 276

A long straight wire of circular cross-section (radius aa) is carrying steady current I.I. The current II is uniformly distributed across this cross-section. The magnetic field is

Show answer and solution

Answer: (B) directly proportional to rr in the region r<ar\lt a and inversely proportional to rr in the region r>ar\gt a

The formula to calculate the magnetic field inside the conducting wire is given by
Bin=μ0Jr2...(1){B}_{\text{in}}=\dfrac{{\mu }_{0}Jr}{2}...(1)
The formula to calculate the magnetic field outside the conducting wire is given by
Bout=μ0Ja22r...(2){B}_{\text{out}}=\dfrac{{\mu }_{0}J{a}^{2}}{2r}...(2)
From equation (1), it can be concluded that the magnetic field is directly proportional to the radial distance inside the wire, whereas from equation (2), it can be concluded that the magnetic field is inversely proportional to the radial distance outside the wire.

JEE Main question paper PDF

Open a shift to read the full paper on this page, or download it.

JEE Main 2025 Apr 2 Shift 1 question paper

Open Download PDF

Opening paper…

Explain it as a whiteboard videoStep-by-step, in Hinglish or English. Your first video needs no login.Solved it on paper but got it wrong?Upload a photo of your working. Mistake Doctor marks the exact line that broke.

More Physics practice

JEE Main Physics practice question on Magnetic Effects & Magnetism (Magnetic Field), with the answer and a step-by-step solution. Scan a question from your own book or paper to get a whiteboard video.