A teacher in his physics laboratory allotted an experiment to determine the resistance (G) of a galvanometer. Students took the observations for 1/3 deflection in the galvanometer. Which of the below is true for measuring value of G? (a) 1/3 deflection method cannot be used for determining the resistance of the galvanometer. (b) 1/3 deflection method can be used and in this case the G equals to twice the value of shunt resistances. (c) 1/3 deflection method can be used and in this case, the G equals to three times the value of shunt resistances. (d) 1/3 deflection method can be used and in this case the G value equals to the shunt resistances.

Answer: (b). With the main current kept the same, 1/3 deflection means Ig = I/3 and the shunt carries 2I/3. Parallel: Ig G = Is S ⇒ I/3G = 2I/3S G = 2S, so the method works. So the answer is (b).

A teacher in his physics laboratory allotted an experiment to… | JEE Main 2022 (25 Jun, Shift 1)

Q113JEE Main 2022 · 25 JUN · SHIFT 1Medium

Kirchhoff's Laws & Measuring Instruments

A teacher in his physics laboratory allotted an experiment to determine the resistance (G) of a galvanometer. Students took the observations for $\frac{1}{3}$ deflection in the galvanometer. Which of the below is true for measuring value of G?

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Answer: (b)

With the main current kept the same, $\frac{1}{3}$ deflection means $I_g = \frac{I}{3}$ and the shunt carries $\frac{2I}{3}$ .
Parallel: $I_g G = I_s S \Rightarrow \frac{I}{3}G = \frac{2I}{3}S$
$G = 2S$ , so the method works.
So the answer is (b).

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