Bruce Andrews, age 9, of Lynn, Mass., for his question:

HOW DOES A MICROWAVE OVEN WORK?

A microwave oven cooks food by using short radio waves that penetrate the food and make its molecules vibrate. Friction among the moving molecules produces heat, which cooks the food.

Microwaves pass through glass, paper and most kinds of china without heating them. Therefore, containers made of those materials may be used to hold food in microwave ovens.

A microwave oven has an electronic vacuum tube called a magnetron that produces microwaves. In most such ovens, the microwaves travel

through a metal tube to the metal blades of a stirrer, a device similar to an electric fan. The moving blades scatter the microwaves into the oven, which has metal walls. The waves bounce from wall to wall until they enter the food in the oven.

Microwave cooking takes much less time than cooking with gas or electric heating units. As an example, a regular oven takes from 45 minutes to an hour to bake one or several potatoes, while a microwave oven can cook a potatoe in about three minutes.