Radio Amateur Quiz Canadian License

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Question A-003-006-001

A meter has a full-scale deflection of 40 microamperes and an internal resistance of 96 ohms. You want it to read 0 to 1 mA. The value of the shunt to be used is:

Correct Answer

4 ohms

Explanation

Let Im=40µA, Rm=96Ω, I_total=1mA=1000µA. Shunt current Ish = I_total - Im = 1000 - 40 = 960µA. Voltage across meter Vm = Im × Rm = 40µA × 96Ω = 3840µV. Shunt resistance Rsh = Vm / Ish = 3840µV / 960µA = 4Ω.

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