question_answer

A wire carrying current I and other carrying\[2I\] in the same direction produce a magnetic field B at the mid-point. What will be the field when \[2I\] wire is switched off?

A) \[B/2\]                                 

B) \[2B\]

C) \[B\]                                     

D) \[4B\]

Correct Answer: C

Solution :

When two parallel conductors carrying current \[I\]and \[2I\] in the same direction, then magnetic field at the mid-point is                 \[B=\frac{{{\mu }_{0}}2I}{2\pi r}-\frac{{{\mu }_{0}}I}{2\pi r}=\frac{{{\mu }_{0}}I}{2\pi r}\] When current \[2I\] is switched off then magnetic field due to conductor carrying current \[I\] is\[B=\frac{{{\mu }_{0}}I}{2\pi r}\]. Hence, option  is correct.