The Student Room Group

A level physics electricity

Can someone explain to me why a voltmeter applied across the terminals of a cell when there is an open circuit shows the emf but when a component is connected making it a closed circuit the voltmeter shows the terminal voltage

Edit: what I'm thinking right now is that when we have an opening in a circuit, the opening has infinite resistance and so it takes up such a large share of the emf that it basically takes up all of it and so from the positive to negative terminal the potential difference is the emf. But when we close the circuit the internal resistance has a share of the voltage (lost volts) and so what is available to the load resistance is lower than the emf therefore the difference in potential is now the terminal voltage. Can someone tell me if what im saying make sense or if im just waffling? Also the mark scheme says its because the current is zero so no internal resistance, can someone explain to what the link is between the internal resistance and the current?
(edited 1 month ago)
Well you're basically right, the internal resistance is still there but with no current going through it there is no voltage drop across it.

Cant really speak for the markscheme without seeing it but a ms is not meant as a model answer, just a bunch of things the examiner can give marks for,, often apparently in no particular order.

Quick Reply

Latest