Circuits in series and in parallel

Philip is putting together a string of lights. But how is he to connect the lights? These particular light bulbs shine properly when they get 1.5 Volts -- precisely the voltage they get from this battery. When Philip connects two bulbs after each other, in series, he notices that each bulb shines weaker than before. These lights are connected in series.

Then the bulbs in the circuit share the voltage supplied by the battery. The voltage is shared equally between the lights. Each bulb gets... 0.75 volts. The more lights that are connected, the weaker they will shine.

This is another effect from connecting in series; if you unscrew a bulb -- or if one breaks -- the circuit is broken, and all the other lights will also go out. Philip wants to be able to replace a lamp, without the others going out. And he wants all the lights to shine more brightly. So he starts over. For a lamp to stay alight, even if you disconnect some of the other lamps, it must have its own wire - like this!

Now, the current can choose more than one way through the circuit. Test it! The lights in this circuit are no longer connected in series, but in parallel. And all the lights shine at full strength! When the circuit is connected in parallel, each bulb receives the full voltage of the battery, even if you connect more light bulbs.

This parallel connection thing seems to be superior. Are there any drawbacks though? Oh yes. In addition to requiring many more wires, there's another important downside: When the current is split into five different paths, it's easier for the electrons to rush through the circuit. So many more electrons can get through, compared to when they had to pass through each and every light bulb.

This draws five times as much current from the battery. Therefore, the battery will discharge faster, than when connected in series. There it is: When connected in series, the bulbs share the voltage from the battery. Every light shines weaker, compared to when there's only one light. If one light is missing, or breaks, in a series connection, the circuit is broken, and all lights go out.

With parallel connection, each light gets the full voltage from the battery, and shines just as brightly -- but the battery discharges faster. And you can disconnect any of the bulbs, without breaking the circuit. It's not just bulbs - and other things that use current - that can be connected in series, or in parallel. Batteries, can also be connected both ways. Like this: These lights shine too weakly, so we want to give them more voltage.

Add some batteries, and connect them, too, in series. When the power sources are connected in series, they feed the circuit with their combined voltage. Three times 1.5 volts is 4.5 volts. Benefits from connecting power sources in series: Higher voltage, brighter light. Drawback: All three batteries run out just as quickly as when you used a single battery.

If you want the batteries to last as long as possible, then connect them in parallel. Like this. Three batteries in parallel give the same voltage as a single battery, but last three times as long. A battery operated light-string still uses up a lot of batteries. That gets expensive.

Maybe better to buy one of those that you connect to the wall outlet instead? Hmm. How does one know if the light-string is connected in series or in parallel? Aha, this one is apparently connected in series. The wall socket voltage is 230 volts.

What's the voltage across each light? No cheating Philip! You can calculate it without looking: 230 volts, divided between ten lamps is... ... that's right. 23 volts!