Question

Current flows through uniform, square frames as shown. In which case is the magnetic field at the centre of the frame not zero ?

• A.
• B.
• C.
• D.

Answer 1

The correct option is C


The magnetic field due to square shape in all options will be zero, because distribution of current will be less in the longer path. But its cumulative effect of magnetic field at centre will be same.

From image $\left(1\right)$
In option (A) and (B) current line is passing through centre, So its perpendicular distance will be zero, so magnetic field in Both (A) and (B) will be zero due to incoming and outgoing current.


From image $\left(2\right)$
Whereas in case of (D) Magnetic field due to incoming current and outgoing current will be equal and opposite. So Net effect is zero.

But in case of (C) Magnetic field will be in same direction with equal magnitude because of the incoming and outgoing current, So net effect will not be zero.
Option C.