A wires of length I is bent into a circular loop of radius R and loop is B. The same wire is now bent into a double loop of equal radii. If both loops carry the same current I and it is in the same direction, the magnetic field at the centre of the double loop will be

Options

A. Zero
B. 2 B
C. 4 B
D. 8 B

Answer

C

Explanation

Magnetic field at the centre of the loop
`B=(mu_(0)ni)/(2pi)`
`(B_(1))/(B_(2))=n_(1)/n_(2)xx.r_(1)/r_(2)`
`implies(B_(1))/(B_(2))=1/2xx(r/2)/r=1/4`
`B_(2)=4B_(1)=4B`