h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I live in a four story building which also has a cellar and an attic.

I recently climbed up into the attic and discovered that there are three light bulbs hanging up there. (The ordinary incandescent type,
100 Watts, no shades). There is a note saying ‘The switches for these lights are in the cellar’.

Down in the cellar I found three switches labelled ‘Switches for lights in attic’. Each switch had it’s own number… 1, 2 and 3 but there is nothing to say which switch controls which lamp, and the lamps weren’t labelled.

Now, I’m getting on in years so I didn’t want to go climbing up and down all those flights of stairs too often (There is no lift) just to find out which switch controls which lamp, but I did want to know in order to be careful with the energy bill, by only switching on the lamp in the area that I need to be.

I thought about it for a few minutes, and half an hour later I left the cellar and went up into the attic and labelled each lamp with the number of the switch controlling it. (For the sake of this puzzle, assume all the lamps do work).

I know I was right, but how did I know which lamp was which ?

Popa, You send the wife up to the attic, then you try each switch, and she yells to you down the stairwell.

Actually, I think I've just worked it out.

Assume all lights were off when you started.

Switch #1 on for five minutes and then off again. Switch #2 on and leave it. Leave Switch #3 off.

When you go upstairs, Bulb #2 will be on, Bulb #1 will be off but warm, and Bulb #3 will be off but cold.

Icy, I thought of suggesting your first solution

Popa, I think it makes more sense if you labelled the switches ( e.g. left, center, right), that would save you from having to go to the attic to look which switch you need, then down to the cellar to switch it on, and then up to the attic again

Smiles... Guess who's not in my missus' good books !

Quite right, although at the speed I get up the stairs, five minutes woudn't be long enough to heat it up enough not to've cooled down again, that's why I didn't leave the cellar for half an hour.

Popa.