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:
- A shunt resistance of 19.5 ohms
- B series resistance of 19 999.5 ohms
- C series resistance of 1 999.5 ohms
- D shunt 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: meters, oscilloscopes, counters, signal generators, and what a reading actually tells you.