This constant motion causes friction, which heats the food. All microwave ovens are electric, and most sit on a counter top. Some units have a shelf in the cavity, which allows more food to cook at one time. But, as cooking quantity doubles, cooking time also nearly doubles. A dial or touch-pad controls the time and power.
All microwave ovens have interlock switches that turn off the oven if the door is opened.
A standard size microwave oven is perfect for slow periods and for cooking individual or small portions. As the quantities get larger, a microwave oven saves little time or energy. Melting chocolate, warming bread, re- heating a pie, or baking a single potato are very appropriate cooking functions. Avoid cooking cheese, whole eggs, cream, pizza, condensed milk, breaded foods, mayonnaise, liver, dry beans and similar foods. In some cases, a microwave oven may not be the best equipment choice.