Electromagnetic Waves and Electromagnetic Spectrum

Electromagnetic waves do not require a material medium. In vacuum they travel with speed: c ≈ 3.00 × 10⁸ m/s Their wavelength and frequency are related by: c = fλ where: `c` = speed of light `f` = frequency `λ` = wavelength As frequency increases: wavelength decreases because their product remains equal to `c` in vacuum. In order of increasing frequency: **Radio → Microwave → Infrared → Visible → Ultraviolet → X-ray → Gamma ray** In the opposite direction, wavelength increases.

Electromagnetic radiation can show: reflection; refraction; diffraction; interference; * polarization.

Electromagnetic radiation also shows particle-like behaviour. Its energy may be exchanged in packets called **photons**. This becomes central in quantum physics.

**c=fλ Photon relation introduced later: E=hf**