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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.
Solution
Half of the loop PQRS is in the region of magnetic field and half in the area of zero magnetic field.
Let us consider a current carrying circular wire, due to which there is uniform magnetic field in the region.
Take a point A inside the loop PQRS in the region where B = 0
According to Ampere's circuital law,
`int B .dl = mu _oi`
If there is current enclosed by the loop PQRS, then magnetic field B cannot be 0.
Whereas, we have taken the magnetic field at point A to be zero.
Thus, such a field is not possible.
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