question_answer

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

A) B/2                                        

B) 2 B         

C) B                                            

D) 4 B

Correct Answer: B

Solution :

When two parallel conductors carry currents \[\text{I}\] 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 (c) is correct.