question_answer

The magnetic flux density B at a distance - from a long straight wire carrying a steac current varies with r as shown in figure

A)                                    

B)

C)

D)

Correct Answer: B

Solution :

                 The magnetic field due to a long wire carrying current Z, at a distance r is given by                                                 \[B=\frac{{{\mu }_{0}}}{2\pi }\frac{I}{r}\] \[\Rightarrow \]               \[B\propto \frac{1}{r}\] Since B is inversely proportional to r, hence correct variation is shown by graph .