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An air-cored solenoid with length 30 cm, area of cross-section 25cm^(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 :`varepsilon=|(dphi_B)/(dt)|` `B=(mu_(0)NI)/(l)=4PIXX10^(-7)xx(500)/(30xx10^(-2))xx2.5` `phi_(B)=BAN=(4pixx10^(-7)xx500xx2.5)/(30xx10^(-2))xx25xx10^(-4)xx500=65.45xx10^(-4)Wb` i.e., Initial flux linkage, `phi_(1)=65.45xx10^(-4)Wb`, Final flux linkage, `phi_(2)=0` `THEREFORE dphi_(B)=-65.45xx10^(-4)Wb` `therefore varepsilon=|(dphi_(B))/(dt)|=(65.45xx10^(-4))/(10^(-3))=6.545V` |
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