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An air-cored solenoid with length 30 cm, area of cross-section 25 "cm"^2 and number of turns 500, carries a current of 2.5 A. The current is suddenly switched off in a brief time of 10^(-3) s. How much is the average back emf induced across the ends of the open switch in the circuit ? Ignore the variation in magnetic field near the ends of the solenoid. |
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Answer» Solution :`B= (mu_0 NI)/(l)` (Inside the solenoid away from the ENDS) `PHI = (mu_0 NI)/(l) A` Total FLUX linkage `= N Phi` `=(mu_0 N^2 A)/(l) I` (Ignoring end VARIATIONS in B) `|epsi| = (d)/(dt) (N Phi)` `|epsi|_(av) = ("total change in flux")/("total time")` `|epsi|_(av) = (4pi xx 10^(-7) xx 25 xx 10^(-4))/(0.3xx10^(-3)) xx (500)^2 xx 2.5` =6.5 V |
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