The following diagrams show
different circuits in which a resistor is connected to one or more cells. In which of the diagrams is the
total emf provided by the cells the greatest? (A), (B), or (C).
In this question, we’re given three
circuit diagrams showing different combinations of cells. We are asked to determine which of
the diagrams shows a combination with the highest total electromotive force. Looking at the diagrams, we can see
that in diagram (A), we are given two cells connected in parallel. In diagram (B), we are given three
cells that are also connected in parallel. But in diagram (C), we are only
given a single cell.
We might think that the more cells
there are in a circuit, the greater the total emf. But let’s remember when multiple
identical cells are connected in parallel within a circuit, the total emf supplied
to the circuit is equal to the emf of any of the cells. And so the number of cells in any
of the circuits shown doesn’t make a difference when it comes to emf.
When we look at circuit (A), we can
see that both cells have equal values of four volts. In circuit (B), the cells have
equal values of two volts. And finally, circuit (C) has just
one cell with an emf of five volts. We have seen that the total emf
supplied to the circuit is equal to the emf of any of the cells. So, we can see from this that the
total emf in circuit (A) is four volts, whereas in circuit (B) it is two volts. Comparing these with circuit (C),
which has an emf of five volts, we see that neither circuit (A) or circuit (B) are
greater than this. So, circuit (C) has the greatest
emf out of the three.
The diagram in which the total emf
provided by the cells is the greatest is circuit diagram (C).