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Electric circuits
2a. Series and parallel: parallel circuits
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Lamps in parallel interactive graphic
Picture 2.4. The lamps in a parallel circuit come on with normal brightness - the same as a single lamp.
Keep them bright
These two lamps are connected in parallel with each other. When the switch is closed, they both light up with normal brightness (the same as a single lamp connected to the cell on its own).

Each lamp feels the full push of the battery.

What's the cost?
You may think that we're getting something for nothing - an extra light on full brightness. However, there is a cost: the battery will run down in half the time. This is because it has to supply twice the current that it did before.
Circuit Challenge 7 - Try it now!
Currents add up - interactive graphic
Picture 2.5. What happens to the current in a parallel circuit?
What happens to the current?
When we connect one lamp to the battery it takes a current of 0.4 amps from the battery. When we connect the second lamp in parallel, it comes on with the same brightness. So it is also taking a current of 0.4 amps. But now what is the current from the battery?

At points X and Y, the current adds up. So the current being taken from the battery is 0.8 amps i.e. twice as much as it was before.

You can see that the two currents flow parallel to one another.

Circuit Challenge 8 - Try it now!
Divide and control
With separate switches, we can control the lamps individually. Check it out: Which switch controls which lamp?

Circuit Challenge 9 and Circuit Challenge 10 - Try them now!

Picture for question 6
Picture 2.6. See question 6.
Question 6
Look at picture 2.6. It shows a circuit that has got a bit jumbled up. Different lamps will come on with different sets of switches.

For each of the switch combinations below, decide which lamps will come on. Then select those lamps using the check boxes.

switches that are closed (on) lamp 1 lamp 2 lamp 3 lamp 4
A only
C only
A and B
A and C
A, B and C
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