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  4. To increase the current sensitivity of a moving coil galvanometer by 50% ,its resistance is increased so that the new resistance becomes twice its initial resistance. By what factor does the voltage sensitivity change ?

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Q. To increase the current sensitivity of a moving coil galvanometer by 50% ,its resistance is increased so that the new resistance becomes twice its initial resistance. By what factor does the voltage sensitivity change ?

Moving Charges and Magnetism

Solution:

Let CS and VS be the original current sensitivity and voltage sensitivity of MCG Changed current sensitivity
$Cs'=Cs +\frac{50}{100}Cs =\frac{3}{2}CS$
since $\,Vs =\frac{Cs}{R}$
changed voltage sensitivity, i.e.,
$VS'=\frac{Cs'}{2R}=\frac{(3/2)CS}{2R}$
$=\frac{3}{4}\left(\frac{CS}{R}\right)=0.75 VS =75% =75%VS$
Thus, voltage sensitivity decreases by 25%