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Photoelectric EffectJEE MathsJEE Chemistry
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JEE Physics
Electromagnetic Spectrum

Electromagnetic Spectrum

The electromagnetic spectrum encompasses the full range of electromagnetic radiation, which includes waves of varying frequencies and wavelengths. It spans from the longest wavelength (radio waves) to the shortest (gamma rays). Key types within the spectrum include microwaves, radio waves, infrared, visible light, ultraviolet rays, X-rays, and gamma rays. Each type has unique properties and applications, such as communication, medical imaging, and remote sensing. Understanding the electromagnetic spectrum is crucial in fields like physics, medicine, and technology.

1.0Definition of Electromagnetic Spectrum

  • The orderly distribution of electromagnetic waves in accordance with their wavelength or frequency into distinct groups having widely differing properties is called the electromagnetic spectrum.
  • The various regions of the electromagnetic spectrum do not have sharply defined boundaries and they overlap. The classification is based roughly on how the waves are produced or detected.

2.0Electromagnetic Waves in EM Spectrum

  • The electromagnetic spectrum spans from radio waves to cosmic rays, listed in increasing frequency and decreasing wavelength: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays, and cosmic rays.
  • The different types of radiation within the electromagnetic spectrum, along with their respective frequency and wavelength ranges, are as follows:

pictorial representation of electromagnetic spectrum and their wavelengths and frequencies.

3.0Waves Generation  

  1. Radio: A radio receives waves from stations, while gases and stars in space also emit radio waves. These waves are mainly used for TV and mobile communication.
  2. Microwave: Microwave radiation aids in cooking and helps astronomers study galaxies and stars.
  3. Infrared: Infrared light, used in night vision goggles, detects heat from our skin and objects. In space, it aids in mapping interstellar dust.
  4. X-ray: X-rays are used in medicine for imaging, in airport security for scanning luggage, and are emitted by hot gases in the universe.
  5. Gamma-ray: Radiations with the highest frequency and the shortest wavelength, making them the most penetrating waves.
  6. Ultraviolet: Sun is the leading source of ultraviolet radiation, responsible for skin tanning and burns. Hot objects in space also emit UV radiation.
  7. Visible: Our eyes can detect visible light, which is emitted by sources like light bulbs and stars.

Example-1. What physical quantity is same for X-rays of wavelength 10−10m red light of wavelength 6800 Å and radio waves of wavelength 500 m?

Solution: The wave speed in vacuum is the same for all radiations: c=3×108m/s


Example-2. A radio can tune to any station in the 7.5 MHz to 12 MHz band.What is the corresponding wavelength band?

Solution:

v1​=7.5MHz=7.5×106Hz

λ1​=v1​c​=7.5×1063×108m/s​=40m

v2​=12MHz=12×106Hz

λ2​=v2​c​=12 ×1063×108m/s​=25m

Thus the wavelength band is 40m-25m

4.0Wireless Communication Bands

Frequency band

Service

540-1600 kHz

Medium wave AM band

3-30 MHz

Shortwave AM band

88-108 MHz

FM broadcast

54-890 MHz

TV Waves

840-935 MHz

Cellular Mobile radio

5.0Electromagnetic Waves In Daily Life

Type

Wavelength Range

Production

Application

Gamma Rays

[<10−3nm]

Radioactive decay of the nucleus

Gamma rays used in

medicine to destroy

cancer cells

X-rays

[<10−3nm to 1nm]

X-ray tubes or inner shell electrons

Treatment of certain

types of cancer

Ultraviolet Rays

[1nm to 400nm]

Inner shell electrons in atoms moving

from one energy level to a lower level

energy level to a lower level

LASIK eye surgery,

Water purifiers

Visible Rays

[400nm to 700nm]

Electrons in atoms emit light when they

move from one energy level to a lower

energy level

Part of the

electromagnetic

spectrum detected by

the human eye.

Infrared Rays

[700nm to 1mm]

Vibration of atoms and molecules

Remote of TV, video

recorders

Microwave

[1mm to 0.1m]

Klystron valve or magnetron valve

Radar systems,

microwave ovens

Radiowave

[>0.1m]

Rapid acceleration and deaccelerations of electrons in aerials

Radio communication

like TV, radio, mobile

communication etc.

Table of Contents


  • 1.0Definition of Electromagnetic Spectrum
  • 2.0Electromagnetic Waves in EM Spectrum
  • 3.0Waves Generation  
  • 4.0Wireless Communication Bands
  • 5.0Electromagnetic Waves In Daily Life

Frequently Asked Questions

The key difference lies in frequency (or wavelength). While all electromagnetic waves travel at light speed in a vacuum, higher frequency means shorter wavelength, and vice versa. This affects how they interact with matter and their various applications.

Our eyes have evolved to detect electromagnetic radiation within a specific range of frequencies, which we call visible light. The molecules in the photoreceptor cells of our eyes are specifically tuned to interact with photons in this frequency range. Radiation outside this range does not trigger the same chemical reactions necessary for sight.

Electromagnetic radiation becomes more dangerous as its energy increases with frequency. Higher-frequency waves can ionize atoms, which can harm DNA and cause health issues. In contrast, lower-frequency waves, such as radio waves, are typically safer.

Cell phones and Wi-Fi use specific portions of the radio wave and microwave parts of the electromagnetic spectrum to transmit information. These frequencies are chosen because they can travel through the air relatively easily and can be modulated to carry data.

Different celestial objects emit different types of electromagnetic radiation. Hot stars emit a lot of visible light and ultraviolet radiation, while cooler objects may emit mostly infrared or radio waves. By observing the universe across the entire electromagnetic spectrum, astronomers get a much more complete picture of the cosmos.

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