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A galvanometer of resistance G can be converted into a voltmeter of range V by connecting in series a high resistance R given by:
AR = G + V
BR = V / I_g − G
CR = G I_g / V
DR = V · G
Answer & Solution
Correct answer: B. R = V / I_g − G
1. Galvanometer gives full deflection at current I_g, so V_g = I_g G.
2. To make it read up to V, drop the excess (V − V_g) across an added series R.
3. At full deflection I_g flows through both, so I_g R = V − I_g G ⇒ R = V/I_g − G.
4. R is large because V/I_g ≫ G typically.
_Source: NCERT Class 12 Physics Ch 3 §3.10 Galvanometer → Voltmeter_
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