`ABCD` is a square loop made of a uniform conducting wire. A current enters the loop at `A` and leaves at `D`. The magnetic field is

Options

A. zero only at the centre of the loop
B. maximum at the centre of the loop
C. zero at all point outside the centre loop
D. zero at all points inside the loop

Answer

C

Explanation

Resistance of `(AB+BC+CD)=3` Resistance of `(AD)`
`i_(1)=i/4, i_(2)=(3i)/4`
At `O`. Magnetic field due to `(AB+BC+CD)` is equal and opposite to magnetic field due to `(AD)`
`B_(O)=0`