Overview
This lecture covers the electromagnetic (EM) spectrum, its main regions, properties, uses, harmful effects, and the role of EM waves in communication systems, including digital and analog signals.
Electromagnetic Spectrum Overview
- The EM spectrum is ordered by wavelength (long to short) or frequency (low to high).
- All EM waves are transverse, travel through a vacuum, and move at 3 × 10⁸ m/s.
- Main regions: radio waves, microwaves, infrared, visible light (red to violet), ultraviolet, x-rays, gamma rays.
- Higher frequency EM waves have more energy and are more harmful (ionizing).
Uses of Electromagnetic Waves
- Radio waves: radio/TV signals, cellular networks, GPS, Wi-Fi, RFID, Bluetooth, radio astronomy.
- Microwaves: satellite TV, mobile phones, radar, cooking (microwave ovens).
- Infrared: electric grills, remote controls, intruder alarms, thermal imaging, optical fibers.
- Visible light: vision, photography, optical fiber communication.
- Ultraviolet: fluorescent markings, tanning, sterilization.
- X-rays: medical imaging, airport security scanning.
- Gamma rays: sterilizing food/equipment, cancer treatment.
Harmful Effects of EM Waves
- Radio waves: no known danger.
- Microwaves: can heat internal organs.
- Infrared: heating effects and potential skin burns.
- Visible light: bright light can damage eyes.
- Ultraviolet: can cause eye damage, skin cancer, cell malfunction.
- X-rays and gamma rays: highly ionizing, can kill cells, cause mutations, and cancer.
- Harm increases with higher frequency and larger doses.
Communication Systems
- EM waves are vital for satellite, mobile phone, Wi-Fi, Bluetooth, and fiber optic communications.
- Geostationary satellites (36,000 km altitude) are used for global broadcasting; polar satellites (200 km altitude) are used for weather and imaging.
- Bluetooth uses radio waves for short-distance device communication.
- Mobile phones and wireless internet utilize microwaves for efficient penetration and short antennae.
- Optical fibers transmit data efficiently using visible and short infrared light.
Digital vs. Analog Signals
- Analog signals vary continuously and can have any value (e.g., traditional telephone).
- Digital signals have two discrete states: 1 and 0 (on/off).
- Digital signals are less affected by noise, can be regenerated, have greater range, allow higher data rates, and support error checking.
- Sound can be transmitted as either analog or digital signals, requiring conversions before and after transmission.
Key Terms & Definitions
- Transverse wave — a wave where oscillations are perpendicular to direction of travel.
- Ionizing radiation — EM waves with enough energy to remove electrons from atoms.
- Analog signal — a continuous signal that can take any value.
- Digital signal — a signal with only two discrete values, usually 1 or 0.
- Geostationary satellite — orbits above the equator with a 24-hour period at 36,000 km altitude.
- Polar satellite — orbits from pole to pole at ~200 km altitude.
Action Items / Next Steps
- Review the main regions and order of the EM spectrum.
- Learn typical uses and risks of each EM wave type.
- Understand differences between digital and analog signals.
- Study how EM waves are used in various communication systems.