A moving coil galvanometer has resistance $50 \Omega$ and it indicates full deflection at 4 mA current. A voltmeter is made using this galvanometer and a $5 \mathrm{k} \Omega$ resistance. The maximum voltage, that can be measured using this voltamenter, will be close to:

JEE Main · 2019 · 09 Apr 2019 · Shift 1 · Current Electricity

A moving coil galvanometer has resistance

50Ω

and it indicates full deflection at 4 mA current. A voltmeter is made using this galvanometer and a

5 k Ω

resistance. The maximum voltage, that can be measured using this voltamenter, will be close to:

(A)15 V
(B)20 V✓ Correct
(C)10 V
(D)40 V

Answer: (B)

Solution

Turning the galvanometer into a voltmeter puts a large resistance in series, and the largest voltage it can read corresponds to full-scale current flowing through both:

V_{ma x} = I_{g} (G + S) = 4 \times 1 0^{- 3} (50 + 5000) = 4 \times 1 0^{- 3} \times 5050 \approx 20.2

V, which is close to

20

JEE Main · 2019 · 09 Apr 2019 · Shift 1 · Single correct option

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