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A rectangular copper coil is placed in a uniform magnetic field of induction 40 mT with its plane perpendicular to the field. The area of the coil is shrinking at a constant rate of `0.5m^(2)s^(-1)`. The emf induced in the coil isA. 10 mVB. 20 mVC. 80 mVD. 40 mV |
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Answer» Correct Answer - B Given, B = 40 mT = `40xx10^(-3)T` Rate of shrinking of area = `0.5m^(2)s^(-1)` `rArr" "(dA)/(dt)=0.5m^(2)s^(-1)` As, `phi=BA cos theta=BA" "[because cos theta=cos 0^(@)=1]` On differentiating with w.r.t. to t, `(dphi)/(dt)=B.(dA)/(dt)=e` `rArr" "e= "induced emf" = 40xx10^(-3)xx0.5=20xx10^(-3)V` = 20 mV |
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