Solved: PHYSICS Question for NEET

NEET PHYSICSMedium

A voltmeter has a resistance of $G$ ohms and range $V$ volts. The value of resistance used in series to convert it into a voltmeter of range $nV$ volts is:

$nG$

$(n-1)G$

$\frac{G}{n}$

$\frac{G}{n-1}$

Step-by-Step Solution

Principle: To increase the range of a voltmeter, a high resistance ( $R$ ) is connected in series with the galvanometer (or existing voltmeter coil) .
Initial Condition: Let $I_g$ be the current required for full-scale deflection. With resistance $G$ and range $V$ , Ohm's law gives $V = I_g G$ .
New Condition: We want the new range to be $V' = nV$ . We connect a resistance $R$ in series. The total resistance becomes $(G + R)$ .
Equation: The new voltage range corresponds to the same full-scale current $I_g$ flowing through the series combination: $V' = I_g (G + R)$ Substituting $V' = nV$ and $I_g = V/G$ : $nV = \frac{V}{G} (G + R)$ $n = \frac{G + R}{G}$ $n = 1 + \frac{R}{G}$ $\frac{R}{G} = n - 1$ $R = (n - 1)G$ .

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