Microwaves are part of the electromagnetic spectrum. Microwaves have lower frequencies and longer wavelengths than visible light. They pass through plastic and glass, and are reflected by metal.
Microwaves with certain wavelengths are absorbed by water molecules and can be used for cooking. Water molecules in the food absorb the microwave radiation which causes them to gain kinetic energy, hence heating the food. Conduction and convection passes this heat energy deeper into the food.
Water in living cells can also absorb microwave radiation. As a result, they can be killed or damaged by the heat released. To prevent this, microwave ovens have shielding that stops the microwaves from reaching people nearby.
Microwave radiation can also be used to transmit signals such as mobile phone calls. Microwave transmitters and receivers on buildings and masts communicate with the mobile telephones in their range.
Certain microwave radiation wavelengths pass through the Earth's atmosphere and can be used to transmit information to and from satellites in orbit.