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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 ϕi. The magnetic flux through the area of the circular coil is given by ϕo. Which of the following option is correct?

1. (1) ϕi < ϕo
2. (2) ϕi > ϕo
3. (3) ϕi = ϕo
4. (4) ϕi = -ϕo

Correct answer: (4) ϕi = -ϕo

Solution

All field lines passing up through the coil return down through the rest of the infinite plane, so the total flux through the plane is zero. Hence phi_i = -phi_o.

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