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The resistance of an ammeter is 13 Ω and its scale is graduated for a current upto 100 amps. After an additional shunt has been connected to this ammeter it becomes possible to measure currents upto 750 amps by this meter. The value of shunt-resistance is

1. 2 Ω
2. 0.2 Ω
3. 2 kΩ
4. 20 Ω

Correct answer: 0.2 Ω

Solution

The shunt resistance is connected in parallel with the ammeter. Using the formula for parallel resistance, Rs = (Ra * I1) / (I2 - I1), where Ra = 13 Ω, I1 = 100 A, and I2 = 750 A, we calculate Rs = (13 * 100) / (750 - 100) = 0.2 Ω.

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