Question Video: Identifying the Combination of Cells with the Greatest emf Science

The 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?

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Video Transcript

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).

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