question_answer

The correct plot of the magnitude of magnetic field \[\overrightarrow{B}\] vs distance r from centre of the wire is, if the radius of wire is R:

A)        

B)

C)       

D)

Correct Answer: B

Solution :

(b)             The magnetic field from the centre of wire of radius R is given by \[B\left( \frac{{{\mu }_{0}}l}{2{{R}^{2}}} \right)r(for\,r<R)\Rightarrow B\propto r\] and \[B=\frac{{{\mu }_{0}}l}{2\pi r}(r>R)\Rightarrow B\propto \frac{1}{r}\] From this description, we can say that the graph (b) is a correct representation.