Explain how you will convert a galvanometer into voltmeter.

Hint: To convert a galvanometer into a voltmeter, a large resistance needs to be connected in series with the galvanometer. This addition increases the device’s total resistance, allowing it to measure potential difference across two points without significantly affecting the circuit current.

 Detailed Explanation:

Let:

• [latex]G[/latex] be the internal resistance of the galvanometer,
• [latex]R[/latex] be the added series resistance, and
•  [latex]V[/latex] the potential difference that the new voltmeter is meant to measure.

If the maximum current the galvanometer can measure is [latex]I_g[/latex], the potential difference [latex]V[/latex] across points [latex]A[/latex] and [latex]B[/latex] is given by:

[latex]V = I_g (R + G)[/latex]

Solving for  [latex]R[/latex], we get:

[latex]R = \frac{V}{I_g} – G[/latex]

This equation provides the required resistance to add in series, so the modified device can accurately measure voltages up to [latex]V[/latex].

Additional Information:

Voltmeters are designed with high resistance to prevent drawing extra current from the circuit, thus ensuring accurate voltage readings. An ideal voltmeter has infinite resistance and is connected in parallel across the component whose potential difference is being measured.

Important Note:

If a simple galvanometer were directly connected in parallel to measure voltage, it would draw current, altering the potential difference in the circuit, resulting in inaccurate measurements. Therefore, high resistance in the voltmeter is crucial to maintain the circuit’s current and ensure precise voltage measurement.