Lights And Switches

Q: There are two rooms. One has three lights and the other has three switches. Bob starts out in the room with the switches. He is alone. He can not see the room with the lights. Once he leaves the the switches room, the door closes and locks. How does Bob figure out which light goes to which switch?

A: Bob turns on a light, leaves a light off, and turns on the light for a few minutes and then turns it off. He leaves the room and sees a light on and two of them off. He touches the two lights to see which is warm and which is cool.