A galvanometer of resistance 50 Ω allows a maximum current of 0.5 mA to flow through it. When a resistance ‘R’ is connected in series with this galvanometer, it converts into a voltmeter of range 0 − 5 V. The value of \( R \) is
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 9950 Ω
A galvanometer is converted into a voltmeter by connecting a high resistance in series with it, chosen so that the full-scale current \( I_g \) flows when the full range voltage V is applied across the combination.
\( \displaystyle V = I_g(G + R) \)
\( \displaystyle R = \frac{V}{I_g} - G = \frac{5\,\mathrm{V}}{0.5\times10^{-3}\,\mathrm{A}} - 50\,\Omega \)
\( R = 10000\,\Omega - 50\,\Omega = 9950\,\Omega \)