Question 1:
difficultTwo coaxial solenoids are made by winding thin insulated wire over a pipe of cross-sectional area A = 10 cm² and length = 20 cm. If one of the solenoids has 300 turns and the other 400 turns, their mutual inductance is
\[\left( \mu=4\pi\times 10^{-7} T m A^{-1}\right)\] :
