The Electromagnetic Spectrum | Geology Optional Notes for UPSC PDF Download

Electromagnetic Spectrum

• Definition: Electromagnetic radiations are waves that travel at the speed of light in a vacuum (3×10^8m/s). These waves consist of electric (E) and magnetic (M) fields that vary sinusoidally and are perpendicular to each other and to the direction of wave progression.
• Key Concepts:
  • Wavelength (λ): The distance between two wave peaks.
  • Frequency (v): The number of wave peaks passing a fixed point per unit time.
  • General Equation: vλ = c (where c is the speed of light).
  • Inverse Relationship: Frequency and wavelength have an inverse relationship.
• Characteristics:
  • Wavelength Measurement: Typically measured in micrometers (µm) or 10^-6 meters.
  • Types of Radiations: Include visible light, gamma rays, X-rays, ultraviolet, infrared, microwaves, TV, and radio waves.
• Explanation: When we mention electromagnetic radiations, we are usually referring to light, which is visible radiation detectable by our eyes. However, the electromagnetic spectrum encompasses a broader range of radiations beyond visible light.
• Examples:
  • Gamma Rays: High-energy electromagnetic radiation often used in medical imaging.
  • Ultraviolet: Responsible for sunburn and tanning of the skin.
  • Infrared: Used in night vision technology and heat detection.
  • Microwaves: Utilized in microwave ovens for cooking food.

Electromagnetic Spectrum Overview

• Gamma Rays: Gamma rays are high-energy waves with a wavelength shorter than 0.1 Angstrom. They find applications in radiotherapy for cancer treatment and sterilization of medical instruments and industrial products.
• X-rays: X-rays have a wavelength range of 0.01 to 10 nanometers and are commonly used in medical diagnosis and industrial applications for inspecting welded joints.
• Ultra-Violet Radiations: Ultraviolet (UV) energy, discovered by Johann Wilhelm Ritter, spans a range of 10 nm to 400 nm. UV light is utilized in sterilization, dental procedures, and various industries.
• Visible Radiations: Visible light, ranging from 0.4 to 0.7 µm, corresponds to the colors perceived by the human eye. Different colors are associated with specific wavelength ranges and find applications in photography.
• Infrared (IR) Radiations: Infrared waves are categorized into near IR, mid IR, and thermal IR, with applications in remote controls, sports injury therapy, and weather forecasting.

Microwaves

• Microwaves have wavelengths ranging from 1mm to 1m.
• They are utilized in various applications such as cooking, mobile phones, radar, aircraft communication, and weather forecasting.
• One of the key advantages of microwaves is their ability to penetrate clouds, smoke, and light rain, making them valuable in communication.

Radiowaves

• Radiowaves have the longest wavelengths and lowest frequencies in the electromagnetic spectrum.
• They are categorized as:
  • Long Wave: Wavelengths around 1-2 km.
  • Medium Wave: Wavelengths approximately 100m.
  • Very High Frequency (VHF) Waves: Wavelengths about 2m, used in communication.
  • Ultra High Frequency (UHF) Waves: Wavelengths less than a meter, employed in Police radio, military aircraft, and television transmissions.
• Remote sensing systems operate within the visible, Infrared, or microwave portions of the spectrum.
• Gamma rays, X-rays, and ultraviolet rays are not suitable for remote sensing due to their high energy levels, while TV and radio waves, being low energy, pose difficulty in signal recording.