Microwave radiation has wavelengths between 1 meter and 1 millimeter and frequencies between 0.3 GHz and 300 GHz. Microwaves travel in a straight line and can pass through materials like plastic and glass but are reflected by metal. Microwaves are absorbed by materials with high water content and produce heat, which is how microwave ovens cook food. A microwave oven uses a high voltage transformer and magnetron to convert electricity into microwave radiation that is reflected inside the chamber. The microwaves cause water molecules in food to vibrate and produce heat for cooking. Microwave radiation does not make food radioactive and requires high levels to potentially cause injuries to body tissue.