0•In electrical circuit, a switch is used to turn the electricity on and off just like a valve is used to turn the water on and off.
•There are times when you want some water but don’t need all the water that the pipe can deliver, so you control water flow by adjusting the faucet.
•Unfortunately, you can’t adjust the thickness of an already thin wire.
•Notice, however, that you can control the water flow by forcing the water through an adjustable length of rocks, as shown to the right.
