MP Board · Class 12 · Physics · Electromagnetic WavesExplain the electromagnetic spectrum in detail. Give the frequency range, wavelength range, sources, and uses of any four types of electromagnetic waves.

Introduction to Electromagnetic Spectrum\nThe classification of electromagnetic waves according to frequency or wavelength is known as the electromagnetic spectrum. It extends from very low frequencies (radio waves) to very high frequencies (gamma rays).

Characteristics

• Electromagnetic waves do not require any material medium for their propagation.
• All electromagnetic waves travel in a vacuum with the same speed, $c = 3 \times 10^8 \text{ m/s}$.
• They are transverse in nature.

1. Radio Waves

• Wavelength Range: $>, 0.1 \text{ m}$
• Frequency Range: $<, 3 \times 10^9 \text{ Hz}$
• Sources: Accelerated motion of charges in conducting wires (oscillating circuits).
• 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 $3 \times 10^{11} \text{ Hz}$
• Sources: Klystron valves, magnetron valves, and Gunn diodes.
• Uses: Radar systems, microwave ovens, long-distance communication via satellites.

3. Infrared Waves

• Wavelength Range: $1 \text{ mm}$ to $700 \text{ nm}$
• Frequency Range: $3 \times 10^{11} \text{ Hz}$ to $4 \times 10^{14} \text{ Hz}$
• Sources: Hot bodies and molecules (heat radiation).
• Uses: Physical therapy for muscular pain, remote controls of TVs, night vision devices, greenhouse effect.

4. Ultraviolet Rays

• Wavelength Range: $400 \text{ nm}$ to $0.6 \text{ nm}$
• Frequency Range: $7 \times 10^{14} \text{ Hz}$ to $5 \times 10^{16} \text{ Hz}$
• Sources: Sun, arc lamps, ionized gases.
• Uses: Sterilizing surgical instruments, purifying water, detecting forged documents, studying molecular structure.