alleryAn ammeter has 0.1 Ω resistance and 1 mA full-scale current. The shunt needed to extend range to 1 A:
A1 × 10⁻⁵ Ω
B1 × 10⁻⁴ Ω
C1 Ω
D1 × 10⁻³ Ω
Answer & Solution
Correct answer: B. 1 × 10⁻⁴ Ω
We have S = I_g G / (I − I_g).
So S = (0.001 × 0.1)/(1 − 0.001) ≈ (1 × 10⁻⁴)/(0.999) ≈ 1 × 10⁻⁴ Ω.
The shunt is very small — diverts most of the 1 A current around the galvanometer.
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