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A millivoltmeter of 25 mV range is to be converted into an ammeter of 25 A range. The value of the necessary shunt resistance, in ohms, is

1. 0.001
2. 0.01
3. 1
4. 0.05

Correct answer: 0.001

Solution

At full scale, the voltmeter drop is 25 mV across the meter. To measure 25 A, the shunt must carry nearly all the current at the same voltage. Using R_sh = V/I = 0.025/25 = 0.001 .

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