JEE Main 2022 · 28 Jun · Shift 1 · Physics Q40

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PhysicsSingle correct+4 / -1Question 40 of 90

An infinitely long hollow conducting cylinder with radius R carries a uniform current along its surface.

Choose the correct representation of magnetic field (B) as a function of radial distance (r) from the axis of cylinder.

B rises linearly to R then stays constant

B against r: linear rise from the origin to r = R, then constant.

B rises linearly to R then falls as 1/r

B against r: linear rise from the origin to a peak at r = R, then a falling curve.

B constant up to R then falls as 1/r

B against r: constant from r = 0 to R, then a falling curve.

B zero up to R, then jumps and falls as 1/r

B against r: zero for r < R, a jump at r = R, then a falling curve.

Answer and worked solution

Official answer: D

Ampere's law. A loop inside the hollow cylinder encloses no current, so $B=0$ for $r<R$ . Outside, $B=\dfrac{\mu_0I}{2\pi r}$ , starting from a jump at $r=R$ .

(D)

Topics:Ampere's circuital law

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JEE Main 2022 · 28 Jun · Shift 1, Physics question 40