Rankers Physics

Measuring Devices ( Galvanometer, Voltmeter and Ammeter & Meter Bridge ): Practice Problem & Solution

A galvanometer of resistance, $G$, is shunted by a resistance $S \text{ ohm}$. To keep the main current in the circuit unchanged, the resistance to be put in series with the galvanometer is : (2011 Mains)
$\frac{S^2}{(S+G)}$
$\frac{SG}{(S+G)}$
$\frac{G^2}{(S+G)}$
$\frac{G}{(S+G)}$

Solution Explained:

To solve this problem, we apply the core principles of Measuring Devices ( Galvanometer, Voltmeter and Ammeter & Meter Bridge ). Understanding the underlying formula is key to arriving at the correct answer below:

To keep the total resistance equal to $G$, the series resistance $R'$ must satisfy $R' + \frac{GS}{G+S} = G$, which simplifies to $R' = \frac{G^2}{S+G}$.

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