question_answer

A coil of one loop is made from a wire of length L and there after a coil of two loops is made from same wire, then the ratio of magnetic field at the centre of coils will be

A)  \[1:4\]          

B)  \[1:1\]

C)  \[1:8\]                         

D)  \[4:1\]

Correct Answer: A

Solution :

          \[{{B}_{1}}=\frac{{{\mu }_{0}}I}{2R}\times N=\frac{{{\mu }_{0}}I\pi }{L};\]  \[{{B}_{2}}=\frac{{{\mu }_{0}}I}{2{{R}_{1}}}\times 2=\frac{4{{\mu }_{0}}I\pi }{L}\] \[\Rightarrow \]\[\]