Electricity_6_Concept

In a series circuit, the electricity has to flow though all of the components in order to complete the circuit. Figure 7 shows an example: if either of the bulbs is broken or removed, the circuit will be broken and no electricity will flow.A switch placed at A, B or C will have exactly the same effect: the circuit will be broken and neither bulb will light. The bulbs will each be dimmer than if there was only one bulb in the circuit. In effect, the power coming from the battery has to be 'shared' between the bulbs,

Parallel circuits

In a parallel circuit, there are alternative routes for the electricity to take. Figure 8 shows an example: if either of the bulbs is broken or removed, a complete circuit will still be possible through the other one. A switch placed at A will be able to break the circuit and operate both bulbs at once, because it will be in series with both of the bulbs. A switch placed at B or C will only break the part of the circuit going to one particular bulb: it will be in series with only one of the bulbs. For the first bulb to work, switches A and B must be closed; for the second bulb to work switches A and C must be closed, Note that if the switch at D were closed, both bulbs would go out since there would be a 'short circuit'. Electricity always takes the path of least resistance, and a connecting wire offers much less resistance than a bulb.

If switches A and B are closed, it will be just the same as having one bulb in a simple circuit. However, when switch C is also closed, both bulbs will be just as bright as one bulb on its own.The catch is that there is only so much energy stored in the battery: to make both bulbs light up as if they were on their own uses up that energy more quickly.The flow of electricity will be greater, causing more power (watts) to be used. Since the battery's voltage cannot change, this means that the current (amps) is greater.

Series and parallel switching

The arrangement of switches can be used to control a circuit in different ways.Two switches can be arranged in series (as in Figure 9) so that both switches need to be closed for the circuit to work. Most domestic wiring is arranged like this, so that one switch acts as a safety check for the other. For example, you have to switch on at both the socket and the appliance for a food mixer to work.

Two switches can also be arranged in parallel (as in Figure 10 so that either switch can be closed to complete the circuit. For example, an intruder alarm may be triggered by the opening of either the front or the back door.

Why you need to know these facts

Components can be connected together to complete a circuit in different ways. these different arrangements affect how the components operate, so an awareness of this is important for constructing and using circuits.

Vocabulary

Parallel circuit: where there is more than one path that the flow electricity can take to complete a circuit.

Series Circuit: where there is only one path for the flow of electricity to take, through all components in the circuit.

Common Misconceptions

The first bulb in the circuit will be the brightest.

This misconception often arises where children have been introduced to the idea that 'electricity comes out of the battery'.

The assumption is that the electricity has to light the first bulb first — then, if there is any electricity left over, it will light the next bulb. Sadly, because the bulbs used in classroom circuits are of poor quality, there is often a marked difference in brightness between two supposedly identical bulbs placed in series. Swap the bulbs over in their bulb holders: the one that was brighter before should still be brighter; so it is the bulb itself, not the position of the bulb, that is the important factor.

Questions

Why won't this circuit work?

This is probably the most common question when children are constructing circuits! Use a methodical approach to help the child check that all the components are in place:

I. Hove you got a complete circuit? Follow the path from one terminal of the battery back to the other terminal, If you can't, reconnect the components to make a complete circuit 2. Is there a short circuit somewhere? Can you complete a circuit without going through any of the devices? (Check especially that wires behind devices aren't touching.) Make sure that the electricity must pass through at least one device in any branch of the circuit, 3.Are the connections secure? Check that the wire has been stripped back enough to make good contact, and that the screw connections are tight (especially bulbs in bulb holders) and show no signs of corrosion.

4. Do the batteries work? Check that each battery used is capable of lighting a bulb of the same voltage.

5.Are you using balanced components (eg a 1.51/ bulb with a 1.5V battery)? If not, swap for ones of a suitable rating.

6. Does each of the components work? Check each one, individually, with a battery that you know works.

7.Ask someone else to look at it — they might spot something that you've missed

8. Take it apart and build it again — carefully this time!

Teaching Ideas

Series and parallel (predicting and testing)

Encourage the children to connect additional bulbs or batteries into a simple circuit after predicting what will happen.

Does it matter which way round a second battery is connected into the circuit? (Yes.)

Does adding an extra bulb change the first bulb's brightness? (Yes if in series, no if in parallel.)

Does it matter where you put the switch? (No if in series, yes if in parallel.)

Mend it (problem solving)

Give the children circuits that don't work and ask them to mend them. Ask them to make incomplete circuits for another group to mend.

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