# Testing Series-wired Christmas Tree Lights

*Most recent answer: 11/26/2014*

Q:

24 christmas light bulb are connected in series. if the bulbs do not light up, atleast one of them s busted. What will be the fastest way of checking which one is busted?

- Jessabel Delos Reyes (age 16)

LaUnion

- Jessabel Delos Reyes (age 16)

LaUnion

A:

Hi Jessabel,

If you test the lamps one by one it will take you on average 12 trials to find the offending one. A more efficient way is to devise some sort of binary chop that will reduce the number of trials to 5 since 2^{5} = 32 and you have only 24 bulbs. One way would be to disconnect a central bulb and measure the resistance between the plug and the contact of the bulb you disconnected. Once you have determined which side is the offending one continue your chop on that side. And so forth.

LeeH

*(published on 11/26/2014)*