In the Ohm's law apparatus shown, which labelled component is connected across the conductor segment XY to measure potential difference? 
AThe ammeter $A$
BThe voltmeter $V$
CThe key
DThe rheostat $Rh$
Answer & Solution
Correct answer: B. The voltmeter $V$
In the figure, the voltmeter is drawn across the ends of the conductor segment XY, which indicates a parallel connection used to measure potential difference across that conductor. The ammeter is in series, so it measures current, not voltage.
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