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Electric circuits
1b. Basic circuits: cells and batteries
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Circuit - interactive graphic
Picture 1.4. A cell pushes current from positive to negative.
What is a cell?
A cell has two ends, labelled + (positive) and – (negative).

A cell pushes the electric current from the positive terminal round to the negative one. This is the way that conventional current flows.

What about electrons?
We always think of an electric current as a flow of positive charges moving from positive to negative.

This convention started before the discovery of the electron and the realisation that electrons carry current in a circuit.

Find out more.

Cells and batteries - interactive graphic
Picture 1.5. Illustration of a cell and a battery.
What is a battery?
Two or more cells can be connected end-to-end to make a battery. A typical cell has a voltage of 1.5 volts (we write this as 1.5 V). By connecting cells in series, we can makes batteries with 3 V, 6 V and so on.

Each battery is labelled with its voltage. This tells us about the ‘push’ it gives to make the current flow.

A 6 V battery gives a bigger push than a 1.5 V cell.

Sometimes we call a single cell a ‘battery’, although technically we ought to say 'cell'.

Circuit Challenge 2 - Try it now!
What do batteries do?
A cell or battery can push an electric current through a lamp. The bigger the voltage, the bigger the push. A bigger push gives a bigger current and the lamp shines more brightly.

Take care! Each lamp is labelled with the biggest voltage it can survive. With too many volts, the current is too big and the lamp will burn out.

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Question 2
Cells must be connected the right way round if their voltages are to add up. If a cell is the wrong way around, then it will push against the others and we have to subtract its voltage.

Look at the batteries below. They are all made from 1.5 volt cells. In each case, decide what its voltage will be. Choose the correct voltage from the drop down list.
[The gold end is the positive and the purple end the negative].

A. Two cells
B. Two cells facing each other
C. Four cells
D. THree cells and one backwards
E. Two cells one way and two the other
Electric current                                                                     Close

Electrons have a negative charge. Therefore they move from the negative terminal to the positive terminal (i.e. in the opposite direction to the conventional current).

It's useful to remember that this is what is happening in the wires. However, we still use the convention that:

electric current flows from positive to negative.