Converting Galvanometer to Voltmeter – Rankers Physics
Topic: Current Electricity
Subtopic: Measuring Devices ( Galvanometer, Voltmeter and Ammeter & Meter Bridge )

Converting Galvanometer to Voltmeter

A galvanometer has a coil of resistance \( 100\ \Omega \) and gives full scale deflection for 20 mA current. If it is to work as a voltmeter of 10 volt range, the resistance required to be added will be:
\( 1000\ \Omega \)
\( 900\ \Omega \)
\( 400\ \Omega \)
\( 500\ \Omega \)

Solution:

To convert a galvanometer to a voltmeter, a high series resistance \( R \) is added: \( R = \frac{V}{I_g} - G \). Substituting values, \( R = \frac{10}{20 \times 10^{-3}} - 100 = 500 - 100 = 400\ \Omega \).

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