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 implies B/(B')=n/(n')xxi/(I')=1/((1//2))xx1/2 =1 implies B'=B`