A long solenoid carrying a current produces a magnetic field B along its axis. If the value of current is halved and the number of turns per unit length is doubled then the new value of magnetic field is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → B
The field inside a long solenoid is \( B = \mu_0 n I \): it is proportional to the product of the turns per unit length and the current.
\( n' = 2n \)
\( I' = I/2 \)
\( B' = \mu_0 (2n)(I/2) = \mu_0 n I = B \)