Question

Sometimes we show an idealised magnetic field which is uniform in a given region and falls to zero abruptly. One such field is represented in figure. Using Ampere's law over the path PQRS, show that such a field is not possible.
Figure

Answer 1

Explanation:

• Half of the PQRS loop is in magnetic field area and half of it is zero magnetic field.

• Let's take a current carrying circular cable, because of which the area has uniform magnetic field.

• Take a point A inside the PQRS loop in the area B = 0

• According to circular rule of Ampere,

               $\int B . d l=\mu_{0} i$  

• If the loop PQRS contains current, then magnetic field B can not be 0.  

• While, at point A we took the magnetic field as zero.

• Such an area is therefore not feasible.

The figure is given in the attachment below.