題組內容

7. Consider a uniformly wound solenoid having \( N \) turns and length \( \ell \). Assume \( \ell \) is much longer than the radius of the windings and the core of the solenoid is air. (10%)

(B) What's the self-induced emf (εL) in the solenoid if the current it carries deceased at the rate of \( dI / dt \)?