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  4. A moving coil galvanometer has 48 turns and area of coil is 4× 10-2m2 . If the magnetic field is 0.2 T, then to increase the current sensitivity by 25% without changing area (A) and field (B) the number of turns should become

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Q. A moving coil galvanometer has 48 turns and area of coil is $ 4\times {{10}^{-2}}{{m}^{2}} $ . If the magnetic field is 0.2 T, then to increase the current sensitivity by 25% without changing area (A) and field (B) the number of turns should become

Rajasthan PMTRajasthan PMT 2010

Solution:

As we know Current sensitivity $ {{S}_{i}}=\frac{NBA}{C} $ $ \Rightarrow $ $ {{S}_{i}}\propto N\Rightarrow \frac{{{({{S}_{i}})}_{1}}}{{{({{S}_{i}})}_{2}}}=\frac{{{N}_{1}}}{{{N}_{2}}} $ $ \Rightarrow $ $ \frac{100}{125}=\frac{48}{{{N}_{2}}}\Rightarrow {{N}_{2}}=60 $