question_answer

Two long straight wires are set parallel to each other at separation r and each carries a current \[I\] in the same direction. The strength of the magnetic field at any point midway between the two wires is

A)  \[\frac{{{\mu }_{o}}I}{\pi r}\]                                     

B)  \[\frac{2{{\mu }_{o}}I}{\pi r}\]

C)  \[\frac{{{\mu }_{o}}I}{2\pi r}\]                                 

D)  zero

Correct Answer: D

Solution :

                 \[{{B}_{1}}=\frac{{{\mu }_{0}}I}{2\pi \left( \frac{r}{2} \right)}\otimes \] ie, upwards                 \[{{B}_{2}}=\frac{{{\mu }_{0}}I}{2\pi \left( \frac{r}{2} \right)}\odot \]      ie, downwards Hence, net magnetic field B is zero.