Q. 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
A) $B$
B) $2\ B$
C) $4\ B$
D) $B/2$
Explanation
(a) $B = \mu_{0}ni \Rightarrow \frac{B}{B^{'}} = \frac{n}{n^{'}} \times \frac{i}{i^{'}} = \frac{1}{(1/2)} \times \frac{1}{2} = 1 \Rightarrow B^{'} = B$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.