# How can you figure out which light switch goes to which light bulb by only making 1 trip upstairs?

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There are 3 switches downstairs, each corresponding to one of the light bulbs upstairs.
How can you figure out which light switch goes to which light bulb by only making 1 trip upstairs?

posted Jan 12, 2018

You turn on one light bulb. Leave it on for a while. Then, turn that one off and turn another one on. Go upstairs. One light bulb will be cold, one will be warm, and one will be on.

When a bulb is left on for some minutes, it will get heated up.
So turn 1st switch on and leave for considerable amount of time so that corresponding bulb will be heated up.
Now turn 1st one off and turn on 2nd one,
Then upstairs.

The bulb which is glowing is of second switch.
The bulb which is hot and not glowing now, is of first switch.
The bulb which is cool and also not glowing is of third switch.

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+1 vote

There are three switches downstairs. Each corresponds to one of the three light bulbs in the attic. You can turn the switches on and off and leave them in any position.
How would you identify which switch corresponds to which light bulb, if you are only allowed one trip upstairs?