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Electromagnetic Spectrum

What is Electromagnetic Spectrum?

Electromagnetic Spectrum is represented by Electromagnetic waves. It’s characterized by their Wavelength or Frequency, linked by the speed of light. The frequency is associated with energy. High frequency is high energy.

The Electromagnetic spectrum covers electromagnetic waves with frequencies ranging from below one hertz to above 10 hertz.

EMS Range of Behavior

The common unit is the electron-volt (eV).

Work done by 1 V potential on 1 electron.

Electromagnetic Spectrum Waves

  • Radio waves
  • Cell phone waves
  • Microwaves
  • Radar waves
  • Infrared waves
  • Visible light waves
  • Ultraviolet waves
  • X-ray waves
  • Gamma waves
RegionWavelength (μm)Remarks
Gamma rays< 3×10-5Incoming radiation is absorbed by the atmosphere.
X-ray3×10-5 – 3×10-3It is absorbed by atmosphere.
Ultraviolet (UV) rays0.03 – 0.4Wavelengths less than 0.3 are absorbed by the ozone layer in the upper atmosphere. Wavelengths between 0.3- 0.4 μm are transmitted and termed as Photographic UV band.
Visible0.4 – 0.7Able to be discovered or identified with film and photodetectors.
Infrared (IR)0.7 – 100Allows maximum Atmospheric transmission.
Portion between 0.7 and 0.9 μm is called photographic IR band, it is detectable
with film. Two principal atmospheric windows exist in the thermal IR region between 3 – 5 μm and 8 – 14 μm.
Microwave103 – 106Mark as rain, fog and clouds. Both active and passive remote sensing is possible. Use Radar wavelength in this range.
Radio>106Have the longest wavelength. Used for some Radars.
[µm represented as microns/micrometers(1000000µm is equal to 1meter.)]

Properties of Electromagnetic waves include: Speed, Frequency and Wavelength.

Speed (s), frequency (f) and wavelength (λ) are related in the formula: is = f x λ

All light waves travel at a speed of 3 x 108 m/s in a vacuum.

Relationship Between Wavelength & Frequency

Wavelength and Frequency have an indirect relationship. That means as wavelength increases, frequency decreases.

Electromagnetic Waves & Energy

High frequency waves have high energy, low frequency waves have low energy.

Radio Waves

Radio waves primarily come from the oscillation of currents in conductors. The long wavelengths travel easily and are not interfered by atoms (Except conductors).

Characteristics of Radio waves
  • Low energy waves with the longest wavelengths
  • Low frequency
  • Includes FM, AM, radar and TV waves
  • Wavelengths of 1 m (10 -1 m) and longer
  • Used in many devices, such as remote control items, cell phones, wireless devices, etc.

The Microwaves are very short wavelength compared to radio waves. Microwaves are associated with the vibrations of some atoms and molecules. Water molecules act as a dipole.

Characteristics of Microwaves
  • Only radio waves are longer
  • Wavelength 1 x 10-1 m to 1 x 10-4 m (1 m to 0.001 m)
  • Used for communication, medicine and consumer use (microwave ovens)
Infrared Waves

Wavelengths longer than visible light are called Infrared rays. Molecules are heated by infrared waves.

Characteristics of Infrared waves
  • Invisible electromagnetic waves that are detected as heat
  • Used in heat lamps
  • Can be detected with special devices such as night goggles
  • Higher energy than microwaves but lower than visible light

The Infra-Red Spectrum

Wave DivisionWavelength (μm)Frequency (THz)Characteristics
Near infra-red0.75-1.4214-400Atmospheric water absorption
Short wave infra-red1.4-3100-214Atmospheric water absorption increases significantly at 1.45 um. 1.53 to 1.56 um is used in long distance communication
Medium wave infra-red3-837-100Heat seeking missiles are designed to work in this spectrum
Long wave infra-red8-1520-37Thermal imaging region
[μm:represent as Microns, also known as micrometer. THz:- Terahertz, a unit of frequency, defined as one trillion (1012) cycles per second or 1012 hertz.]
Visible Light

Visible light is radiation in a narrow band of wavelength. Many atoms and molecules have specific behavior at unique frequencies of light. Corresponds to maximum output from the Sun.

Characteristics of Visible Light
  • Narrower ranges are colors (400 nm to 800 nm)
  • The portion of the Electromagnetic spectrum that human eyes can detect.
  • Visible Light- ROY G BIV (red, orange, yellow, green, blue, indigo, violet)
  • Red has the lowest frequency, violet is the highest
Ultraviolet Waves

Ultraviolet rays have shorter wavelengths than visible light. Some molecules absorb ultraviolet and remit visible light.

Characteristics of Ultraviolet
  • Higher energy than light waves
  • Can cause skin cancer and blindness in humans
  • Used in tanning beds and sterilizing equipment

X-rays are associated with energetic transitions in atoms. The short wavelength x-rays can penetrate materials.

Characteristics of X-rays
  • High energy waves
  • Continuous spectra result from electron bombardment
  • Used in medicine, industry and astronomy
  • Can cause cancer
Gamma Rays

Gamma rays are photons associated with nuclear or particle processes. Acceleration of a very energetic charged particle gives x-rays and gamma rays, it’s Called bremsstrahlung.

Characteristics of Gamma rays
  • The highest energy
  • Energy range overlaps, soft gamma equals hard x-ray
  • Blocked from Earth’s surface by Atmosphere

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