## Aadarsh 3 years ago A light bulb is hanging in a room. Outside of the room there are three switches, of which only one is connected to the lamp. In the starting situation, all switches are 'off' and the bulb is not lit. If it is allowed to check in the room only once to see if the bulb is lit or not (this is not visible from the outside), how can you determine with which of the three switches the light bulb can be switched on?

1. apoorvk

NAHI!! i typed out a long solution for this one but lost it due to server restart. that alien feeling _/(o.O)\_ okay so a similar question was also posted by Prof Walter Lewin recently(albeit easier) (though I managed to cracked it there as well :p) SO, name the three switches as A, B and C. Now switch on A, say for about 15 mins. Then switch it off. Now, switch on B. and immediately enter the room. Now the following are results corresponding to what you find inside: A- if the bulb is unlit, but the glass cover outside is hot due to radiations from the filament. B- if the bulb is is lit. C- if the bulb is BOTH unlit, as well as feels cold, or room temperature-like. Am I right? :)

@sheena101 didi, can u try this?

4. sheena101

no idea :D

@sheena101 Please give me a medal also.

7. heena

better ask ur freind to stand in the room and den ask him when light i lit he will shout and tell u simple :P

8. ujjwal

is there a key hole in the door??

9. apoorvk

unfortunately, your friend is very busy according to question, and currently unavailable.

10. apoorvk

:D @heena

@heena didi, ur response is a bit witty. But, the thing is that only one person is allowed to do this. I think, @apoorvk bhaiya's answer is correct. Anyway, thanks my sister.

@sheena101 didi, thanks for the medal. Yippee!!!!!

@ujjwal bhai, there is no key hole in the door as given.

14. heena

ok guys i forgot to write dat i was joking dat time actually i had a cutt off anyways apporv an is right i think evn i also dunno :P