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Series Circuits and Christmas Lights

A series circuit is a closed electrical circuit that is connected so that the current passes through each circuit element in turn without branching off.

This series circuit shows four resistances in sequence with a battery.


In a series circuit, the current going to each element (light bulb etc.) in the circuit goes through every element in order. If one element was to burn out, the entire circuit would burn out and no flow of electricity would result. If you add an extra element to this type of circuit, you will need to increase the voltage to have the same total voltage as before. If you remove an element out of this type of circuit, you will need to decrease the voltage to have the same total voltage as before. The following rules applying to Series Circuits.

V= voltage R= resistance I = current.

1. The sum of the potential drops equals the potential rise of the source.
V(total) = V (1) + V (2) + V (3) + . . .

2. The current is the same everywhere in the series circuit.
I (total) = I (1) = I (2) = I (3) = . . .

3. The total resistance of the circuit is equal to the sum of the
individual resistances.
R (total) = R (1) + R (2) + R (3) + . . .


You return from the shopping mall with your new Icicle Christmas Lights and are excited to put them up on the house. While unpacking them you accidentally drop a set on the floor and one bulb breaks, but there are thousands of bulbs, and you are too anxious to put them up to find which one is broken. You don’t think that it will affect the lights, and continue to spend the next couple of hours installing the lights on your house. When you’re finally done you flip the power on, but the lights don’t turn on. It turns out that your new icicle lights have been wired in series and since one bulb is broken, none of them will work. You now have to pull all the lights off and spend time finding and replacing the broken bulb.

Making sure you know if the circuit is run in series is important, and choosing a parallel circuit type appliance over a series circuit type appliance is always a good idea when given the choice.


What if the majority of electrical circuits were wired in series rather than in parallel?

Answer: If circuits were wired in series, it could get very time consuming to locate the source of the problem when a circuit goes out, and could be costly if you have to hire someone to fix the problem. It would also be a safety hazard if safety systems such as turn signals in vehicles and street lights in cities were wired in series because the system would fail completely if a bulb burnt out.

more series circuit problems

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Gregory Shepertycky

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