An Ideal Solenoid of Length 10 Cm Consists of a Wire

Multiple Choice

An ideal solenoid of length 10 cm consists of a wire wrapped tightly around a wooden core. The magnetic field strength is $4.0 \mathrm {~T}$ inside the solenoid. If the solenoid is stretched to 25 cm by applying a force to it, what does the magnetic field become?

A) 1.6 T
B) 10.0 T
C) 20 T
D) 4.0 T