A current carrying circular coil is bent so as to convert it into a double loop, both the loops being concentric and are carrying current in the same direction. If B is the initial magnetic field at the centre, the final magnetic field at the centre will be

Options

A. zero
B. B
C. 2B
D. 4B

Answer

d

Explanation

`B_("Initial")=(mu_(0)i)/(2r)`
`B_("final")=(mu_(0)i)/(2(r/2))+(mu_(0)i)/(2(r/2))=B_("final")=(2mu_(0)i)/r=4B_("initial")`