Electromagnetic Spectrum and Radio Waves

Electromagnetic Spectrum

• Composed of various types of waves, each with different wavelengths and frequencies.
• Waves range from radio waves (longest wavelengths) to gamma rays (shortest wavelengths).
• The spectrum's visible light portion is what humans can see.

Radio Waves

• Have the longest wavelengths in the EM spectrum.
• Used for transmitting radio and television signals.
• Transmission and reception depend on oscillating charges.
• When encountering a radio receiver's antenna system, small electric oscillations are created, synchronizing with antenna vibrations.
• Radio development initially focused on wireless telegraphy.
• The first fixed semaphore system (visual telegraphy) was developed in the 1790s in Europe.
• Electrical communication systems appeared in the 1830s.
• Early experiments in electrical telegraphy, such as one by Samuel Thomas von Sommering (1809), employed electrochemical methods.
• Sir Charles Wheatstone and Sir William Fothergill Cook developed the first commercial electrical telegraph in England.
• James Clerk Maxwell mathematically demonstrated the propagation of electromagnetic waves through free space.
• Heinrich Rudolf Hertz and others demonstrated radio wave propagation on a laboratory scale.
• Nikola Tesla experimented with the transmission and radiation of radio frequency energy. He proposed telecommunication of information via radio waves.

Microwaves

• Extremely high-frequency radio waves.
• Have very short wavelengths, ranging from approximately one millimeter to 30 centimeters.
• Used in telecommunications (e.g., mobile phones).
• Used in fixed traffic speed cameras.
• Used in cooking food.
• Used in radar to determine range, altitude, direction, or speed of various objects (aircraft, ships, spacecraft, missiles, motor vehicles, weather formations).

Infrared

• EM radiation with a wavelength longer than visible light.
• Discovered by Sir William Herschel in 1800.
• Microscopically, infrared light is typically emitted or absorbed by molecules when their rotational-vibrational movements change.
• Used in various applications. Infrared thermal imagery can detect temperature differences.

Visible Light

• Portion of EM radiation visible to the human eye.
• Light waves are emitted by hot objects.
• Red has the longest wavelength, violet the shortest.
• Other colors have wavelengths and frequencies inbetween these two extremes.
• All colors combined create white light.

Ultraviolet

• EM radiation with wavelengths shorter than visible light but longer than X-rays.
• Named for frequencies higher than human-perceived violet.
• Used for preventing document counterfeiting (watermarks).
• Useful in crime scenes (identifying bodily fluids).
• Excessive exposure can cause skin cancer, melanoma, and eye issues (e.g., photokeratitis).

X-rays

• High-energy waves with significant penetrating power.
• Widely used in medical applications and weld inspection.
• Known as Röntgen radiation in many languages, named after Wilhelm Conrad Röntgen (1895).
• Overexposure can contribute to cancers such as leukemia.
• Can be used in radiotherapy (treating cancer using high-frequency X-rays).

Gamma Rays

• Generated by radioactive atoms and nuclear explosions.
• Used in various medical applications.
• More penetrating than X-rays.
• Used in certain cancer treatments (Gamma Knife Surgery).