8.1 Introduction
Electromagnetic waves are waves of electric and magnetic fields that propagate through space. They are produced by accelerating charges and can travel without any medium, unlike sound waves.
8.2 Displacement Current
- Displacement current was introduced by Maxwell to modify Ampere’s Law.
- Occurs in capacitors when electric field changes, even though no real current flows.
- Displacement current density:
Jd=ϵ0∂t∂E
- Ensures continuity of current and predicts electromagnetic waves.
8.3 Electromagnetic Waves
- Maxwell’s equations predict that a time-varying electric field produces a magnetic field, and a time-varying magnetic field produces an electric field.
- These self-sustaining fields propagate as electromagnetic waves at the speed of light:
c=μ0ϵ01
- Characteristics:
- Transverse waves
- Electric field (E), magnetic field (B), and direction of propagation are mutually perpendicular
- Do not require a medium
8.4 Electromagnetic Spectrum
Electromagnetic waves cover a wide range of frequencies:
| Type of Wave | Wavelength | Frequency | Example / Use |
|---|---|---|---|
| Radio waves | > 1 m | < 3×10⁸ Hz | Broadcasting |
| Microwaves | 1 m – 1 mm | 3×10⁸–3×10¹¹ Hz | Radar, cooking |
| Infrared | 1 mm – 700 nm | 3×10¹¹–4.3×10¹⁴ Hz | Remote control |
| Visible | 700–400 nm | 4.3×10¹⁴–7.5×10¹⁴ Hz | Light perception |
| Ultraviolet | 400–10 nm | 7.5×10¹⁴–3×10¹⁶ Hz | Sterilization |
| X-rays | 10–0.01 nm | 3×10¹⁶–3×10¹⁹ Hz | Medical imaging |
| Gamma rays | < 0.01 nm | > 3×10¹⁹ Hz | Cancer treatment |
- Applications: Communication, medicine, industry, and scientific research.