Q 12-04-145JEE MainJEE Main 2022 (25 Jun, Shift 2)Easy
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 magnetic field will be equal to
Answer: (D) $B$
$B = \mu_0nI$. With $n\to\dfrac n2$ and $I\to2I$, the product $nI$ is unchanged, so the field stays $B$.
Solution by Sreeraj P, M.Sc Physics