MP Board · Class 12 · Physics · Electromagnetic WavesWhat are electromagnetic waves? Explain their characteristics and write the complete electromagnetic spectrum in order of increasing frequency, mentioning one use of each type.

Introduction to Electromagnetic Waves\nElectromagnetic (EM) waves are waves that are created as a result of vibrations between an electric field and a magnetic field. Unlike mechanical waves, they do not require any material medium for their propagation and can travel through a vacuum. They travel with the speed of light in vacuum, which is approximately $3 \times 10^8\text{ m/s}$. James Clerk Maxwell predicted their existence through his famous Maxwell's equations, and Heinrich Hertz later produced them experimentally.

Key Characteristics of Electromagnetic Waves

• Origin: Accelerated charges are the source of all electromagnetic waves. An oscillating charge produces an oscillating electric field, which in turn produces an oscillating magnetic field.
• Nature: They are transverse in nature, meaning the electric field vector and magnetic field vector oscillate perpendicular to each other as well as to the direction of wave propagation.
• Speed: In free space, the speed of EM waves is given by $c = \frac{1}{\sqrt{\mu_0 \varepsilon_0}}$, where $\mu_0$ is the permeability of free space and $\varepsilon_0$ is the permittivity of free space.
• Energy and Momentum: They carry both energy and linear momentum through space. The energy is shared equally between the electric field and the magnetic field vectors.

The Electromagnetic Spectrum\nThe electromagnetic spectrum encompasses all types of EM waves arranged according to their frequency and wavelength. In order of increasing frequency (decreasing wavelength), the spectrum is:

1. Radio Waves:

   • Frequency Range: $< 10^9\text{ Hz}$
   • Use: Used extensively in radio and television communication systems.

2. Microwaves:

   • Frequency Range: $10^9\text{ Hz} - 3 \times 10^{11}\text{ Hz}$
   • Use: Used in microwave ovens and radar systems for aircraft navigation.

3. Infrared Waves:

   • Frequency Range: $3 \times 10^{11}\text{ Hz} - 4 \times 10^{14}\text{ Hz}$
   • Use: Used in physical therapy to relieve muscle pain and in TV remote controls.

4. Visible Light:

   • Frequency Range: $4 \times 10^{14}\text{ Hz} - 7.5 \times 10^{14}\text{ Hz}$
   • Use: It provides the sensation of sight and helps us see the surrounding world.

5. Ultraviolet (UV) Rays:

   • Frequency Range: $7.5 \times 10^{14}\text{ Hz} - 3 \times 10^{16}\text{ Hz}$
   • Use: Used in water purifiers to kill harmful bacteria and germs.

6. X-Rays:

   • Frequency Range: $3 \times 10^{16}\text{ Hz} - 3 \times 10^{19}\text{ Hz}$
   • Use: Used in medical diagnostics to detect bone fractures.

7. Gamma Rays:

   • Frequency Range: $> 3 \times 10^{19}\text{ Hz}$
   • Use: Used in cancer treatment to destroy malignant tumor cells.