Two Solenoids Are Each Made of 2 000 Turns of Copper

Multiple Choice

Two solenoids are each made of 2 000 turns of copper wire per meter. Solenoid I is 2 m long, while solenoid II is 1 m long. When equal currents are present in the two solenoids, the ratio of the magnetic field B_I along the axis of solenoid I to the magnetic field B_II along the axis of solenoid II, B_I/B_II, is

A) 1/4.
B) 1/2.
C) 1.
D) 2
E) 4.