Solenoid 2 Has Twice the Radius and Six Times the Number

Multiple Choice

Solenoid 2 has twice the radius and six times the number of turns per unit length as solenoid 1.The ratio of the magnetic field in the interior of 2 to that in the interior of 1 is:

A) 1/3
B) 1
C) 2
D) 4
E) 6