What makes the toaster pop up in a toaster ?

The Secret to the toaster is a special switch located inside. It is made of two metals .As the toaster gets hot the heat on the two metals makes the switch begin to blend . When the toast is ready the bending switch shuts off the electricity. At the same time the switch triggers a spring that pop up.

Metal expands when is it heated, but each kind of metal expands a different amount. A bimetal switch is made of two kinds of metal. One of them will expand more than other, so the switch bends when it heats up.

Refrigerators, irons and other home appliances use bimetal switches to keep their temprature constant .