Electromagnetic Radiation Overview

Electromagnetic Radiation

• Electromagnetic radiation (EMR) is a ubiquitous phenomenon.
• It takes the form of self-propagating waves in a vacuum or matter.
• EMR consists of electric and magnetic field components.
• These components oscillate in phase, perpendicular to each other and the direction of energy propagation.

Types of Electromagnetic Radiation

• Electromagnetic radiation is classified by frequency or wavelength.
• Types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.
• Radio waves are used for wireless communication (radio, TV, cell phones, WiFi).
• Microwaves are used in microwave ovens, radar, and satellite communication.
• Infrared radiation is used in night vision, remote controls, and industrial heating.
• Visible light is used for human vision, photography, and fiber optics.
• Ultraviolet radiation is used for sterilization, fluorescence, and curing processes (e.g., ink curing).
• X-rays are used in medical imaging (radiography, CT scans) and industrial inspection.
• Gamma rays are used in medical imaging (PET scans), cancer treatment, and industrial material inspection.

Electromagnetic Spectrum

• The electromagnetic spectrum visualizes the relationship between wavelength, frequency and types of radiation.
• Longer wavelengths correspond to lower frequencies.
• Shorter wavelengths correspond to higher frequencies.
• Wavelength is measured in meters, and frequency in Hertz (Hz).

Properties of Electromagnetic Radiation

• A small, variable range of frequencies is sensed by the eyes and is known as visible light.
• EMR carries energy and momentum.
• EMR interacts with matter.
• EMR travels at the speed of light (c = 2.998 x 10⁸ m/s).
• EMR is a transverse wave.

EMR Wave-Particle Duality

• EMR exhibits wave and particle properties (wave-particle duality).
• Confirmed through experiments.
• In the wave aspect, EMR exhibits interference and diffraction patterns.
• In the particle aspect, EMR particles (photons) have well-defined positions and momenta.

Parameters of a Wave

• Amplitude (a): Maximum vertical value of a single cycle.
• Wavelength (λ): Distance between two adjacent crests or troughs. Measured in Angstroms or millimicrons. (1Å = 10^-8 cm, 1 mµ = 10^-7 cm)
• Crests: Highest points of a wave.
• Troughs: Lowest points of a wave.

Electromagnetic Waves (diagram)

• Electromagnetic waves are transverse waves.
• The waves oscillate perpendicular to the direction of propagation.

Wave Number

• Wave number is the reciprocal of wavelength. It is defined as the total number of waves that can pass through a space of one cm.
• Wave number is expressed in cm^-1.

Frequency

• Frequency (v) is the number of waves that pass a point in one second, measured in Hz.
• Frequency is inversely proportional to wavelength.
• The equation relating frequency and wavelength is: c= λv , where c is the speed of light.

Example Frequency Calculation

• Visible light wavelength range is 3800-7600 Å.
• Using c = λv , one can calculate the corresponding frequency range.