Difference between Power pack voltage and voltmeter reading?

Question

When a power pack is set onto a particular voltage (example: 6 volts), why does the voltmeter sometimes give a reading slightly different (example: 5.6 volts)?

This is not an error in reading the voltmeter, as it was pointed out by our teacher and we were asked to research it.

Thank you in advance.

Answer 1

cheap power supplies can be way off, although with no load, they usually read high, not low.

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Answer 2

There are various ways of measuring voltage, and only for measuring smooth DC (such as you would get from a battery) will all such measurements be the same (except for instrument errors, of course).  If there is ripple because the DC has been made from AC, the instrument might measure the average voltage, the peak voltage, or possibly the RMS voltage.  Galvanometer type voltmeters measure average; electronic instruments vary.

Answer 3

Duff voltmeter.

If a voltmeter has its correct internal impedance of infinity, then it will read an accurate voltage. So either the rating on the pack is incorrect or the voltmeter is duff.