Q.A voltmeter of resistance $1000\ \Omega$ can measure up to 25 V. How will you convert it so that it can read up to 250 V?

This ratio (deflection / voltage) is called the voltage sensitivity of the instrument.

A voltmeter is a galvanometer connected in series with a high resistance. Its voltage sensitivity is defined as the deflection theta produced per unit voltage V applied across it, i.e. voltage sensitivity = th …

A galvanometer becomes a voltmeter by adding a high resistance in series; the same full-scale deflection current must flow in both configurations, so we first find $I_g$ from the $2\,\text{V}$ setup, then calculate the series resistance needed for $10\,\text{V}$. The answer is (C) $5.2\,\text{k}\Omega$.

Adding a large series resistance limits the current through the galvanometer coil and extends the range so it can measure large potential differences directly.

A galvanometer is a sensitive instrument that gives full-scale deflection for only a very small current, and it has some small internal (coil) resistance $G$. To use it as a voltmeter capable of reading a potential difference V, a high resistance R is connected in series with it, chosen so that:

$V = I_g (G + R)$

…

Connecting a high resistance in series with a galvanometer converts it into a voltmeter of the desired range.

A galvanometer alone can only detect small currents and has a small, fixed full-scale voltage rating (since its coil has resistance $G$). To use it as a voltmeter capable of measuring a chosen larger range of potential difference $V$, a high resistance $R$ is connected in series with the galvanometer coil, so that at full-scale deflection current $I_g$, $V = I_g(G+R)$, giving $R = \dfrac{V}{I_g} - G$. This series resistance both extends the voltage range and ensures the …

A galvanometer is converted into a voltmeter by putting a large resistance in series with it, so that most of the applied voltage drops across this resistance rather than across the (delicate, low-current) galvanometer coil.

A galvanometer of coil resistance $G$ gives full-scale deflection for a small current $I_g$. To use it to measure a larger potential difference $V$ across some element, we connect a high resistance $R$ in series with the galvanometer. The combination (galvanometer + R) is then connected across the points whose voltage is to be measured. The value of $R$ needed for the voltmeter to read up to $V$ at full-scale deflection is found from: …

A voltmeter needs high internal resistance so it draws minimal current, and is inserted in parallel with the element being measured — this is achieved by adding a large series resistance to the galvanometer.

Reasoning

A voltmeter is connected in parallel across the component whose voltage is to be measured. For it to disturb the circuit as little as possible, it must draw very little current — i.e. it must have a very high resistance overall. This is achieved by connecting a high resistance $R$ in series with the galvanometer coil; the combination then has resistance $G+R \approx R$ (large), and a known fraction of the potential dif …

A galvanometer is converted into a voltmeter by connecting a high resistance in series with it.

A galvanometer is a sensitive instrument that gives full-scale deflection for a very small current, and it has a small resistance $G$. A voltmeter must:

1. Draw only a small current from the circuit across which it measures the potential difference (so it doesn't disturb the circuit).
2. Have as HIGH a resistance as possible so that it draws negligible current.

To achieve this, a high resistance $R$ is connected in SERIES with the galvanometer. If $I_g$ is the full-scale deflection current of the galvanometer and $V$ is the voltmeter range to be measured, then …