Are Christmas Lights in Series or Parallel? — wired.com

Why don’t your Christmas lights work? Sadly, in the event of a string of lights going out on your tree replacing the strand is usually the best option. It’s pretty difficult to find that one bulb that’s causing the problem. However, this is a great time to look at the difference between series and parallel circuits. Just about the simplest circuit you can create uses just one battery and one light bulb. In one fun activity, you can give a person one wire, one battery and one light bulb. Ask the person to make the bulb shine. It’s possible to get it to work, but it can still cause some trouble for people.

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