How can we determine the self-inductance of a solenoid?

[bdh2991]

Homework Statement

For one of the problems in my homework it asks to prove that L=μAN^2/length ...i didnt have a problem with that osrt but the second part states a spring is 5cm long and has a diameter of .15 cm with 50 coils...how much self-inductance must you include for it to model as an ideal solenoid?

Homework Equations

L=AN^2μ/length

The Attempt at a Solution

I think I am just confused on what they mean by ideal solenoid...i ended up getting the answer right by just pklugging the numbers in but could someone explain what an ideal solenoid is?

 

[EmittingLight]

Sorry I can't help you with this self-inductance business, but I do know that an ideal solenoid is one in which the magnetic field lines are completely straight parallel lines inside and outside of the solenoid.

Real solenoids actually have bent magnetic field lines, which curve outwards when leaving the solenoid, and curve inwards when entering.