The Box

Saint_ · Post by **Saint_** » Thu Apr 25, 2013 10:28 am

A light bulb is placed in a solid metal box with a lid. The lid is switched so that if it is opened, the light goes off instantly.

There are two switches on the outside of the box. One lights the light, the other does nothing.

How can you tell which switch is the working one?

Post by **Oscar Namechange** » Thu Apr 25, 2013 10:31 am

Open the lid ?

YZGI · Post by **YZGI** » Thu Apr 25, 2013 10:33 am

Turn one on then open box and see if the light is warm. If not it's the other switch?

Saint_ · Post by **Saint_** » Thu Apr 25, 2013 10:42 am

YZGI;1425327 wrote: Turn one on then open box and see if the light is warm. If not it's the other switch?

We have a winner! That was fast.

Bruv · Post by **Bruv** » Thu Apr 25, 2013 12:16 pm

You could always drill a small hole and close the lid in a darkened room...................but why bother...... there is no need for a light in an empty box anyway:-2

tude dog · Post by **tude dog** » Thu Apr 25, 2013 1:30 pm

Saint_;1425328 wrote: We have a winner! That was fast.

Yea, that was clever, I liked it.

Only thing I came up with was checking the switches with a volt meter, though I knew that wasn't really in the spirit of the question.

tude dog · Post by **tude dog** » Thu Apr 25, 2013 1:31 pm

Bruv;1425330 wrote: You could always drill a small hole and close the lid in a darkened room...................but why bother...... there is no need for a light in an empty box anyway:-2

Yea, thanks for that. There is always one in the crowd.

Scrat · Post by **Scrat** » Thu Apr 25, 2013 5:16 pm

You probably could also use dust or metal filings. If the light is on in the box there is current flow which create lines of force. Put the material around the switch and see what it does. I don't have the means to test the theory but I'd bet it would work in some form. There would also be a temperature difference most likely but it may not be sensible with touch.

I'd just open the box and check the bulb.