Consider an Ideal Solenoid of Length L, N Windings, and Radius

Multiple Choice

Consider an ideal solenoid of length L, N windings, and radius b (L is much longer than b) . A current I is flowing through the wire windings. If the length of the solenoid becomes twice as long
(to 2L) , but all other quantities remained the same, the magnetic field inside the solenoid will

A) become one-half as strong as initially.
B) become twice as strong as initially.
C) become one-fourth as strong as initially.
D) remain the same.
E) become four times as strong as initially.