Advanced Qualification · A-003 Measurements · A-003-006-002
A moving-coil milliammeter having a full-scale deflection of 1 mA and an internal resistance of 0.5 ohms is to be converted to a voltmeter of 20 volts full-scale deflection. It would be necessary to insert a:
- Ashunt resistance of 19.5 ohms
- Bseries resistance of 19 999.5 ohms
- Cseries resistance of 1 999.5 ohms
- Dshunt resistance of 19 999.5 ohms
Correct answer: B — series resistance of 19 999.5 ohms. From the official ISED question bank, verified word for word.
Why
To turn a tiny current meter into a voltmeter that reads up to 20 volts, you must add a large resistor in series to limit the current so only 1 mA flows at full scale. The full explanation — and one for every question — is in Pro.
Practise this section
Measurements is section A-003 of the Advanced exam: Measurements: meters, oscilloscopes, counters, signal generators, and what a reading actually tells you.
Drill A-003 — free, no account