Question

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/2 

(b) B 

(c) 2 B

(d) 4 B

Answer 1

Correct option  (b) B 

Explanation:

Magnetic field induction at point inside the solenoid of length l, having n tums per unit length carrying current I is given by

B = μ₀ni

If I → doubled n → halved then B → remains same.