A square loop of side as and a straight long wire are placed in the same plane as shown in figure. The loop has a resistance `R` and inductance `L`. The frame is turned through `180^@` about the axis `OO^'`. What is the electric charge that flows through the loop?

Answer

4

Explanation

After moving the loop about side `PQ` through `120^(@)` the normal on the side `PS` from the wire will be passing through midpoint `C` and net magnetic, flux through the loop in the new position will be zero.
`:.` Changes is flux `/_\f=` Flux through the loop in the initial position

`dphi=vecB.dvecA(mu_(0)I)/(2pix)a.dx`
`phi=int_(a)^(2a)(mu_(0)Iadx)/(2pix)=(mu_(0)Ia)/(2pi)ln(2)`
`:.` charge flown through the square loop `=(/_\phi)/R=(mu_(0)Ia)/(2piR)In (2)`