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Series and Parallels

Series and Parallels

As long ago as 1810, many larger cities had street lighting. An electric current was made to jump between two carbon rods - this was called electric arc lighting. First introduced by Sir Humphry Davy, these lamps were connected in series. This meant that all the lamps were connected as a part of one large circuit. It also meant that if one lamp went out, and the circuit was broken, they all went out. This often happens with Christmas tree lights, although they can be arranged in parallel circuits to avoid this problem. It was Thomas Edison who recognised the need to use parallel circuits for street lighting. Each bulb in a parallel circuit has a circuit of its own. If one bulb fails, the others will continue to glow - the current is divided equally between them.

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You will need two large boards, drawing pins, insulated wire, bulbs, bulb-holders and batteries. The drawing pins can act as contacts where your wires join.
 

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Set up your parallel circuit. If one bulb fails the other will remain alight because the circuits are separate. Observe how brightly the bulbs glow.
 

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Replace one of the bulbs in the parallel circuit with another battery. Does the light from the bulb change? Now wire up a series circuit like the red one shown here. Include one bulb and two batteries in this circuit.

 

 Why It Works

series circuit

A series circuit uses one path to connect the bulb and battery. If two batteries are used, the bulb glows twice as brightly as it would with one. Two bulbs in a series circuit would not glow brightly as one. A parallel circuit provides more than one path for the current. Each bulb receives the same voltage (amount of power) even if another battery or bulb is added or removed. If two batteries are used in a parallel circuit, their power does not combine as in the series circuit. The bulb receives the voltage of one battery, but glows for double the time

Bright Ideas
Add another bulb to the series circuit -what do you notice when the current is switched on? Now add another one. What difference does this make? Draw a series circuit diagram.
Wire another bulb into the parallel circuit. What do you notice about the glow from the bulbs? Draw a parallel circuit diagram.
For how long do the bulbs in each kind of circuit stay alight? Which type of circuit is most wasteful of energy?

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05. Observe this bulb. Does it shine as brightly as the bulb in the yellow parallel circuit? Try removing one battery. Which bulb is shining the brightest now?