Video Transcript
The diagram shows three cells
connected in series. The total emf provided by the cells
is eight volts. What is the emf provided by the
third cell?
In this question, we are shown
three cells connected in series. The question states that the total
emf produced by these three cells is eight volts.
We know that when components are
connected in series, there is only one path that an electric current can take
through the components. The cells are connected in series,
so the single path that current can take must pass through all of the cells. This means that the potential
difference between the ends of the path must be increased by each cell on the
path.
Looking at our circuit diagram, we
have three cells and we can see that the two cells that are labeled produce emfs of
four volts and three volts. We know that these cells combined
with the unlabeled cell must produce a total emf of eight volts. The emf due to cells with known
emfs is four volts plus three volts. We can then subtract the emfs due
to these two cells from the total emf, recalling that the total emf is eight
volts. So subtracting both four volts and
three volts from eight volts gives a result of one volt. Therefore, the third cell produces
an emf of one volt.
