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Question:

A galvanometer having a coil resistance of 100Ω gives a full scale deflection when a current of 1 mA is passed through it. The value of the resistance which can convert this galvanometer into an ammeter giving a full scale deflection for a current of 10 A, is?

0.01Ω

2Ω

0.1Ω

3Ω

Solution:

When full-scale current is flowing, potential difference, V = 1 mA × 100Ω = 0.1 V
Let shunt resistance be R. Current flowing through R in full scale reading is Ish = 10 A - 0.001 A = 9.999 A
V = IshR
0.1 V = 9.999 A × R
R ≈ 0.01 Ω