A galvanometer has a coil of resistance 200 Ω with a full scale deflection at 20. The value of resistance to be added to use it as an ammeter of range (0 - 20) mA is: (a) 0.40 Ω (b) 0.10 Ω (c) 0.20 Ω (d) 0.50 Ω

Answer: (c). A shunt is needed: S = (Ig G)/(I - Ig). S = 20 × 10⁻⁶ × 20020 × 10⁻³ - 20 × 10⁻⁶ = 4 × 10⁻³19.98 × 10⁻³ ≈ 0.20 Ω So the answer is (c) 0.20 Ω.

A galvanometer has a coil of resistance 200 Ω with a full scale… | JEE Main 2024 (9 Apr, Shift 1)

Q45JEE Main 2024 · 9 APR · SHIFT 1Easy

Kirchhoff's Laws & Measuring Instruments

A galvanometer has a coil of resistance $200\ \Omega$ with a full scale deflection at $20\ \mu\text{A}$ . The value of resistance to be added to use it as an ammeter of range $(0 - 20)\text{ mA}$ is:

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Answer: (c)

A shunt is needed: $S = \frac{I_g G}{I - I_g}$ .
$S = \frac{20 \times 10^{-6} \times 200}{20 \times 10^{-3} - 20 \times 10^{-6}} = \frac{4 \times 10^{-3}}{19.98 \times 10^{-3}} \approx 0.20\ \Omega$
So the answer is (c) $0.20\ \Omega$ .

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