NCERT · Class 12 · Physics · Electromagnetic WavesExplain the electromagnetic spectrum in detail, mentioning the wavelength range, frequency range, production method, and uses of each type of electromagnetic wave.

Introduction to Electromagnetic Spectrum\nThe electromagnetic (EM) spectrum is the entire range of all types of electromagnetic radiation. Radiation is energy that travels and spreads out as it goes—the visible light that comes from a lamp in your house and the radio waves that come from a radio station are two types of electromagnetic radiation. Other examples of EM radiation include microwaves, infrared light, ultraviolet light, X-rays, and gamma-rays.

Classification of Electromagnetic Waves

1. Radio Waves

   • Wavelength Range: $> 0.1 \text{ m}$
   • Frequency Range: $< 3 \times 10^9 \text{ Hz}$
   • Production: Rapid acceleration and deceleration of electrons in aerials (antennas).
   • Uses: Radio and television communication systems, cellular phones.

2. Microwaves

   • Wavelength Range: $0.1 \text{ m}$ to $1 \text{ mm}$
   • Frequency Range: $3 \times 10^9 \text{ Hz}$ to $3 \times 10^{11} \text{ Hz}$
   • Production: Klystron valves, magnetron valves, and Gunn diodes.
   • Uses: Radar systems in navigation, microwave ovens for cooking, long-distance communication via satellites.

3. Infrared (IR) Waves

   • Wavelength Range: $1 \text{ mm}$ to $700 \text{ nm}$
   • Frequency Range: $3 \times 10^{11} \text{ Hz}$ to $4 \times 10^{14} \text{ Hz}$
   • Production: Vibration of atoms and molecules in hot bodies.
   • Uses: Night vision devices, physical therapy for muscle aches, remote controls for electronic devices, greenhouse effect monitoring.

4. Visible Light

   • Wavelength Range: $700 \text{ nm}$ to $400 \text{ nm}$
   • Frequency Range: $4 \times 10^{14} \text{ Hz}$ to $7 \times 10^{14} \text{ Hz}$
   • Production: Radiated by excited electrons in atoms as they drop to lower energy levels.
   • Uses: Provides the sensation of sight, photosynthesis in plants, optical photography.

5. Ultraviolet (UV) Rays

   • Wavelength Range: $400 \text{ nm}$ to $1 \text{ nm}$
   • Frequency Range: $7 \times 10^{14} \text{ Hz}$ to $3 \times 10^{17} \text{ Hz}$
   • Production: Inner shell electrons in atoms moving from higher to lower energy levels, and special lamps like the Sun.
   • Uses: Water purification (killing bacteria), detecting forged documents, LASIK eye surgery.

6. X-Rays

   • Wavelength Range: $1 \text{ nm}$ to $10^{-3} \text{ nm}$
   • Frequency Range: $3 \times 10^{17} \text{ Hz}$ to $3 \times 10^{19} \text{ Hz}$
   • Production: Sudden deceleration of high-speed electrons hitting a heavy metal target (Coolidge tube).
   • Uses: Medical diagnostics (detecting bone fractures), security scans at airports, crystallography.

7. Gamma Rays

   • Wavelength Range: $< 10^{-3} \text{ nm}$
   • Frequency Range: $> 3 \times 10^{19} \text{ Hz}$
   • Production: Radioactive decay of atomic nuclei and nuclear reactions.
   • Uses: Cancer treatment (radiotherapy) to destroy malignant cells, food sterilization.