There's a room with a 1cupper coffee maker in it.
The door to the room is closed.
There are 3 switches on the wall outside the room next to the door.
One of them is connected to the coffee maker. All 3 switches are "off".
You can only have one switch "on" at a time
and you may open the door and go in only once.
How can you determine which switch is connected to the coffee maker?
A true friend steps in when the rest of the world steps out.