A) B/2
B) 2B
C) B
D) 4B
Correct Answer: C
Solution :
When currents in both the wries are in same direction, then magnetic field at the centre \[B={{B}_{2}}-{{B}_{1}}\] \[=\frac{{{\mu }_{0}}(2I)}{2\pi (r/2)}-\frac{{{\mu }_{0}}I}{2\pi (r/2)}\] \[=\frac{{{\mu }_{0}}I}{\pi r}\] When\[2I\]wire is switched off, then magnetic field at the centre \[B=\frac{{{\mu }_{0}}I}{2\pi (r/2)}\] \[=\frac{{{\mu }_{0}}I}{\pi r}=B\]
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