A long solenoid carrying a current produces a magnetic field `B` along its axis. If the current is doubled and the number of turns per cm is halved, the new value of the magnetic field is

Options

A. B
B. 2 B
C. 4 B
D. B/2

Answer

A

Explanation

`B = mu_(0) nI`
`(B_(1))/(B_(2)) = (n_(1))/(n_(2)) xx (I_(1))/(I_(2)) = (1)/((1//2)) xx (1)/(2) implies B_(1) = B_(2) = B`