A galvanometer has a resistance of 50 \(\Omega\) and a current of 2 mA is needed for its full scale deflection. Calculate resistance required to convert it, (i) into an ammeter of 0.5 A range. (ii) into a voltmeter of 10 V range.

Q.24 A galvanometer has a resistance of 50 \(\Omega\) and a current of 2 mA is needed for its full scale deflection. Calculate resistance required to convert it, (i) into an ammeter of 0.5 A range. (ii) into a voltmeter of 10 V range.

Doubtly Asked 28 Oct 2026 Board exam · March 2025 hsc 12th Save WhatsApp Report

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Answer: (i) shunt \(S \approx 0.2008\ \Omega\) in parallel; (ii) series resistance \(R = 4950\ \Omega\).

Given: \(G = 50\ \Omega\), \(I_g = 2\) mA \(= 2 \times 10^{-3}\) A.

(i) Ammeter of range \(I = 0.5\) A: a low resistance (shunt) \(S\) is connected in parallel. Since \(I_gG = (I - I_g)S\),

\[S = \frac{I_gG}{I - I_g} = \frac{2 \times 10^{-3} \times 50}{0.5 - 0.002} = \frac{0.1}{0.498} \approx 0.2008\ \Omega\]

(ii) Voltmeter of range \(V = 10\) V: a high resistance \(R\) is connected in series. Since \(V = I_g(G + R)\),

\[R = \frac{V}{I_g} - G = \frac{10}{2 \times 10^{-3}} - 50 = 5000 - 50 = 4950\ \Omega\]

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A galvanometer has a resistance of 50 \(\Omega\) and a current of 2 mA is needed for its full scale deflection. Calculate resistance required to convert it, (i) into an ammeter of 0.5 A range. (ii) into a voltmeter of 10 V range.

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