Overview
This lecture covers the properties, uses, and hazards of microwave and infrared radiation, both of which have long wavelengths and low frequencies on the electromagnetic spectrum.
Microwave Radiation
- Microwaves have relatively long wavelengths and low frequencies.
- Microwaves that are not absorbed by water molecules are used for satellite communications, as they can pass through Earth's atmosphere.
- Satellite communication involves microwaves being transmitted from Earth, received by a satellite, then retransmitted back to Earth and received by satellite dishes.
- Microwaves absorbed by water molecules are used in microwave ovens to heat food.
- In microwave ovens, microwaves cause water molecules in food to vibrate, spreading energy and heating the food via conduction or convection.
- Foods with more water heat up faster in microwaves.
Infrared Radiation
- Infrared (IR) radiation is emitted by all objects with thermal energy (heat).
- The hotter an object, the more infrared radiation it emits.
- Infrared cameras detect IR radiation, allowing us to see warm objects in the dark.
- Warm-blooded animals appear bright in infrared images due to higher IR emission, while cooler surroundings appear darker.
- Infrared radiation is used in cooking by heating metals in ovens or grills, causing them to emit IR radiation that cooks food.
- Unlike microwaves, infrared radiation only heats the surface of food, which is why bread toasts rather than just warming up.
- Electric heaters use electrical energy to heat metal, which then emits IR radiation to warm the surrounding air.
Hazards of Microwave and Infrared Radiation
- Both microwaves and infrared radiation are only harmful in large amounts.
- Everyday background radiation from these sources is generally not harmful.
- High levels of microwaves can boil and destroy living cells.
- High levels of infrared radiation (e.g., putting a hand in a toaster) can cause burns and cell destruction.
Key Terms & Definitions
- Microwave Radiation — Electromagnetic waves with long wavelengths, used for communication and cooking.
- Infrared Radiation (IR) — Electromagnetic radiation emitted by objects due to heat; used in imaging and heating.
- Conduction — Heat transfer through direct contact between molecules.
- Convection — Heat transfer through movement of fluids (liquids or gases).
Action Items / Next Steps
- Review the main uses and hazards of microwave and infrared radiation.
- Be prepared to explain differences between microwave heating and infrared heating.