Sources and Detection of Electromagnetic Waves

1. Radio Waves
   Sources: Radio transmitters, electric circuits
   Detectors: TV and radio aerials, radar receivers
2. Microwaves
   Sources: Microwave ovens
   Detectors: Microwave receivers
3. Infrared (IR)
   Sources: The sun, warm and hot objects, human bodies
   Detectors: Photodiodes, light-dependent resistors (LDR), skin, photographic films
4. Visible Light
   Sources: Sun, lamps, lasers
   Detectors: Human eyes, photo cells, photographic films
5. Ultraviolet (UV)
   Sources: Sun, electric arcs, mercury vapor lamps
   Detectors: Photocells, photographic films, fluorescent chemicals
6. X-rays
   Sources: X-ray tubes
   Detectors: Photographic films, fluorescent screens
7. Gamma Rays
   Sources: Radioactive nuclei, cosmic rays
   Detectors: Geiger-Müller tubes, spark counters

Frequency and Wavelength

• Frequency: It is the number of waves occurring per second, measured in Hertz (Hz). Radio waves have the lowest frequencies, while gamma rays have the highest.
• Wavelength: It is the distance covered by one complete wave cycle, measured in meters (m). Radio waves have the longest wavelengths, while gamma rays have the shortest.

Electromagnetic Wave Bands

Electromagnetic waves are arranged in increasing frequency:

• Radio waves: >10−3 to 104 m 
• Infrared: 10−6 to 10−3 m
• Visible light: 10−6 to 10−7 m
• Ultraviolet: 3.5×10−7 to 10−9 m
• X-rays: 10−11 to 10−9 m
• Gamma rays: 10−11 m

Subdivisions of Radio Waves

Radio waves are classified by their frequency into bands:

• ELF: Extremely Low Frequency
• VHF: Very High Frequency
• UHF: Ultra High Frequency

Wavelengths of Radio Waves

Radio waves can also be classified by their wavelengths as:

• Long waves
• Medium waves
• Short waves

Energy in Electromagnetic Waves

Electromagnetic waves carry energy that increases with frequency. Gamma rays are the most energetic, while radio waves carry the least energy.