A student finds two ancient meters with numbered scales but no unit markings. He thinks that one is an ammeter and one is a voltmeter but doesn't know which is which. He measures the resistance of each, finding that meter A has a resistance of 5000 ohms and meter B has a resistance of 0.10 ohm. He can conclude that
A) B is the voltmeter and A is the ammeter.
B) A is the voltmeter and B is the ammeter.
C) A is the voltmeter but B cannot be a useful meter.
D) B is the voltmeter but A cannot be a useful meter.
E) neither can be a useful meter.

Question

Quizplus · Accepted Answer

Ammeters are designed to have very low resistance so they can be placed in series with a circuit without significantly affecting the current flow, hence meter B with 0.10 ohm is the ammeter. Voltmeters, on the other hand, need to have high resistance so they can be placed in parallel across a portion of a circuit without drawing significant current, making meter A with 5000 ohms the voltmeter.

A Student Finds Two Ancient Meters with Numbered Scales but No