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Question
A voltmeter consists of a 25 Ω coil connected in series with a 575 Ω resistor. The coil takes 10 mA for full-scale deflection. What maximum potential difference can be measured by this voltmeter?
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Solution
It is given that for maximum current, i = 10 mA, the potential drop across the voltmeter will be maximum.
The effective resistance of the circuit,
\[R_{eff} = \left( 575 + 25 \right) \Omega = 600 \Omega\]
The maximum value of potential difference measured,
V = Reff × i
= 600 × 10 × 10−3
= 6 V
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