21.2 Electromagnetic Waves
Electromagnetic Waves
| MAXWELL’S EQUATIONS |
|---|
| 1. Electric field lines originate on positive charges and terminate on negative charges. (Gauss’s Law) |
| 2. Magnetic field lines form closed loops. (Gauss’s Law of Magnetism) |
| 3. A varying magnetic field induces an emf and an electric field. (Faraday’s/Lenz’s Laws) |
| 4. A varying electric field (like from moving charges/currents) generates magnetic fields. (Ampere’s Law) |
Maxwell predicted the existence of electromagnetic waves having perpendicular oscillating electric and magnetic fields that travel at the speed of light (3.0×108m/s).
| ELECTROMAGNETIC WAVES | ||
|---|---|---|
| • Transverse waves with oscillating electric and magnetic fields • E and B fields are perpendicular to the velocity. |  | |
| Energy Density ofthe Electric Field | uE = ½ ε0 E2 ε0 = 8.85×10-12 (10-12C2 / N•m2) | |
| Energy Density ofthe Magnetic Field | uB = 1 / 2µ0 B2 µ0 = 1.26×10-6 (C2 / N•m2) | |
| Speed of Light in aVacuum | c = E / B = 1 / √ ε0 µ0 = 3.0×108 m/s | |
| Wavelength andFrequency | λ f = c λ = wavelength f = frequency |  |
| Intensity ofSpherical Waves | I = P / A = P / 4 π r2 | |
| Doppler Effect | fo ≈ fs (1 + u/c) | u = relative speed of observer & source fo = frequency observed fs = frequency emitted (source) |