A cell shows 1.60 V on a high-resistance voltmeter but its terminal voltage falls to…
PHYSICS · Single correct · A Level · Physics · Electricity · Electricity
Problem
A cell shows 1.60 V on a high-resistance voltmeter but its terminal voltage falls to 1.45 V when it drives a current through a lamp. Which statement correctly explains the fall in voltage?
(a) The emf of the cell itself immediately falls from 1.60V to 1.45V as the chemicals are used up when current flows.
(b) Part of the energy per coulomb is expended in overcoming the cell’s internal resistance when current flows.
(c) The high–resistance voltmeter draws an appreciable current, so it shows a larger reading than the true emf; once the lamp is connected the reading falls.
(d) When the lamp filament heats up its resistance rises, increasing the total circuit resistance and thereby reducing the terminal voltage of the cell.