Switch and Bulb

In your room there are three light switches in the OFF position. The corresponding 3 bulbs are in the upstair room. You may 'switch on' or 'switch off' any of the switches but you may only go upstairs to inspect the bulbs only once. How can you determine the switch for each bulb with one inspection?

Answer:

Turn switch 1 and 2 on for a while .. about 5 mins or so. Then turn switch 2 off. After that go upstair and inspect the bulbs by touching them. The lit bulb is controlled by switch 1. Of the two unlit bulbs, the hot bulb is controlled by switch 2 and the unlit and cold bulb is controlled by switch 3.