JEE Main · 2020 · 07 Jan 2020 · Shift 1 · Magnetic Effects of Current

Consider a circular coil of wire carrying constant current

I

, forming a magnetic dipole. The magnetic flux through an infinite plane that contains the circular coil and excluding the circular coil area is given by

ϕ_{i}

. The magnetic flux through the area is given by

ϕ_{0}

. Which of the following is correct?

(A) $ϕ_{i} = - ϕ_{0}$ ✓ Correct
(B) $ϕ_{i} > ϕ_{0}$
(C) $ϕ_{i} = ϕ_{0}$
(D) $ϕ_{i} < ϕ_{0}$

Answer: (A)

Solution

Magnetic field lines always close on themselves, so every line that threads through the area of the coil must return through the rest of the infinite plane surrounding it. Whatever flux

ϕ_{0}

passes through the coil in one sense therefore reappears in the surrounding region in the opposite sense, and because the net flux through a complete plane for a closed field is zero, the two contributions must exactly cancel, giving

ϕ_{i} = - ϕ_{0}

JEE Main · 2020 · 07 Jan 2020 · Shift 1 · Single correct option

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JEE Main · 2020 · 07 Jan 2020 · Shift 1 · Magnetic Effects of Current

Solution

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