Current Electricity

JEE Main level, single correct, medium

313 of 380

Question 313 of 380

A moving coil galvanometer of resistance 100Ω100 \Omega shows a full scale deflection for a current of 1 mA. The value of resistance required to convert this galvanometer into an ammeter, showing full scale deflection for a current of 5 mA, is ____\_\_\_\_ Ω\Omega

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Answer: (D) 25

To convert a galvanometer to an ammeter, a shunt resistance SS is connected in parallel. For full-scale deflection:
Current through galvanometer: Ig=1I_g = 1 mA
Total current: I=5I = 5 mA
Current through shunt: Is=5−1=4I_s = 5 - 1 = 4 mA
Since voltage across both is equal: Ig⋅G=Is⋅SI_g \cdot G = I_s \cdot S
0.001×100=0.004×S0.001 \times 100 = 0.004 \times S
S=0.10.004=25S = \frac{0.1}{0.004} = 25 Ω

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