An air cored solenoid is of length 0.3m, area of cross section is `1.2xx10^(-3) m^(2)` and has 2500 turns. Around its central section, a coil of 350 turns is wound. The solenoid and the coil are electrically insulated from each other. Calculate the emf induced in the coil if the initial current of 3A in the solenoid is reversed in 0.25s.

Explanation

`M=(mu_(0)N_(1)N_(2)A_(2))/(l)`
`=(4pi xx 10^(-7) xx 2500 xx 350 xx 1.2 xx 10^(-3))/(0.3)H=4.4 xx 10^(-3) H`
`e=M(dI)/(dt)" "e=4.4 xx 10^(-3) xx (3-(-3))/(0.25)V=0.1056V`
`***` If two solenoids are of unequal length, then length of bigger solenoid is to be considered.