ALTERNATING-CURRENT CIRCUITS — Edward Purcell & David Morin
Physics — E&M · self-inductance-solenoid-doubling
Problem
Doubling a solenoid *
((a)) Two identical solenoids are connected end-to-end to make a solenoid of twice the length. By what factor is the self-inductance increased? The answer quickly follows from the formula for a solenoid's L, but you should also explain in words why the factor is what it is.
((b)) Same question, but now with the two solenoids placed right on top of one another. (Imagine that one solenoid is slightly wider and surrounds the other.) They are connected so that the current flows in the same direction in each.