A Solenoid of Length 18 Cm Consists of Closely Spaced

Multiple Choice

A solenoid of length 18 cm consists of closely spaced coils of wire wrapped tightly around a wooden core. The magnetic field strength is 2.0 mT inside the solenoid near its center when a certain current flows through the coils. If the coils of the solenoid are now pulled apart slightly, stretching it to 21 cm without appreciably changing the size of the coils, what does the magnetic field become near the center of the solenoid when the same current flows through the coils? (μ₀ = 4π × 10^-7 T ∙ m/A)

A) 1.7 mT
B) 3.4 mT
C) 0.85 mT
D) 2.0 mT