OAK Holland Trading

and then this...
Schematic 2.2k

There are two rooms.
In one room there are three switches, in the other room there is one filament lamp.
The lamp is connected to one of the switches only but the wiring is not visible in either room.
You can play with the switches as much as you want.
You can enter the other room to inspect the lamp only once!
How can you find out to which switch the bulb is connected?

Solution