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 magnetic field will be equal to

• A. B
• B. 2B
• C. 4B
• D. $\frac{B}{2}$

Answer 1

Answer: (A)

B

Answer 2

The correct option is(A): B

B = μ0 ni

Now i → 2 i

And

$n→\frac{n}{2}$

$B'=μ_0\frac{n}{2}×2i=μ_0ni=B$