Q5 on the 2005 NSW HSC chemistry paper: electrochemical cell
This question shows two beakers of salt solution connected by a salt bridge. Each beaker also contains one metal electrode, and these electrodes are connected via a voltmeter. No comment is made about whether the voltmeter is ideal.
Four sets of observations are listed, and students are asked to state which is true.
For any of the sets of observations to be true, a current must flow in the circuit, which means that a finite current must flow through the voltmeter. Of course the voltmeter does have a finite resistance so a very small current will flow.
However, one could argue that the nicest answer to the question might have been "very little will happen, because a voltmeter has a very high internal resistance, so the current will be very small".
This is one of the problems with multiple choice questions: what does the bright student do if the best answer is not there?
A forum designed mainly for high school physics students in New South Wales, Australia.
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