41. Microwaves & Infrared Radiation

1. Microwaves

Microwaves have relatively long wavelengths and low frequencies. They are generally split into two categories based on their interaction with water.

Communication (Satellite TV & Phones)

• Property: These microwaves are not absorbed by water molecules.

• Process: They can pass through the Earth's atmosphere (which contains water vapor) to reach satellites in orbit.

• Result: The signal is received by the satellite and transmitted back to Earth to be picked up by satellite dishes.

Cooking (Microwave Ovens)

• Property: These microwaves are absorbed by water molecules.

• Process: When fired at food, the energy is absorbed by the water molecules, causing them to vibrate.

• Result: This energy is transferred to neighboring molecules via conduction or convection, heating the food from the inside out.

2. Infrared (IR) Radiation

Infrared radiation is emitted by all objects that have thermal energy. The hotter an object is, the more IR radiation it emits.

Infrared Cameras

• Use: Used to see in the dark or identify living organisms.

• Process: Special cameras detect the IR radiation emitted by objects rather than visible light.

• Result: Warm objects (like animals) appear bright, while cooler surroundings appear dark.

Cooking & Heating

• Ovens, Grills, and Toasters: These use hot metal filaments to emit IR radiation.

• Electric Heaters: Use electrical energy to heat metal, which then emits IR radiation to warm a room.

• Key Difference: Unlike microwaves, IR radiation does not penetrate deep into food; it mostly heats the surface (e.g., toasting bread).

3. Safety and Hazards

• Low Quantities: Background levels of microwave and IR radiation are generally harmless.

• High Quantities:

  • Microwaves: Can cause internal heating of body cells, effectively "boiling" and destroying them.

  • Infrared: Can cause skin burns as the radiation destroys surface cells.

4. Summary Table