Overview
This lecture explains the main uses of each type of electromagnetic wave and the reasons why specific waves are suitable for those uses.
Radio Waves
- Used to transmit radio and terrestrial TV signals (received via aerials, not satellite/cable).
- Travel long distances before being absorbed by obstacles.
- Longer wavelengths can diffract (spread) between hills.
- Reflect off the ionosphere, allowing transmission around the Earth.
Microwaves
- Used to heat food because water molecules absorb microwave energy, increasing temperature.
- Used for satellite communication as microwaves pass through the atmosphere without being reflected or refracted.
Infrared
- Emitted by electrical heaters and used to cook food in ovens, as energy is absorbed easily by surfaces.
- Infrared cameras detect heat loss in buildings.
Visible Light
- Used for communication through fiber optics (thin glass fibers transmitting light pulses).
- Carries telephone and cable TV signals due to its short wavelength, allowing high information capacity.
Ultraviolet
- Used in energy-efficient light bulbs; ultraviolet is created and then converted to visible light inside the bulb, using less energy.
- Used in sun tanning (e.g., tanning beds), but increases the risk of skin cancer and causes premature aging.
X-rays and Gamma Rays
- Both used for medical imaging; x-rays visualize broken bones, gamma rays detect cancers.
- Both are very penetrative, passing through body tissue.
- X-rays are absorbed by bones, making them visible on images.
- Both can be used in cancer treatments.
Key Terms & Definitions
- Terrestrial TV — Television received via ground-based (not satellite/cable) antennas.
- Diffraction — The spreading of waves when they pass through gaps or around edges.
- Ionosphere — A layer of charged particles in Earth's atmosphere that reflects radio waves.
- Fiber Optics — Thin glass fibers transmitting light signals for communication.
- Penetrative — The ability of electromagnetic waves to pass through materials.
Action Items / Next Steps
- Learn and memorize the specific uses of each electromagnetic wave type as outlined.
- Review workbook questions on electromagnetic spectrum uses if available.