Electromagnetic Waves and the Spectrum

Electromagnetic (EM) waves are transverse waves that transfer energy. Unlike sound, they don't need a medium to travel through—they can pass through the vacuum of space. This is why we can see light from distant stars.

All EM waves travel at the same speed in a vacuum: 3 × 10⁸ m/s (the speed of light). They obey the wave equation: v = fλ.

The EM spectrum is arranged by wavelength (and frequency). From longest wavelengthto shortest:

Visible light is only a tiny portion of the spectrum—the part our eyes can detect. It ranges from red (longest wavelength, ~700 nm) to violet (shortest, ~400 nm).

Higher frequency waves carry more energy. UV, X-rays, and gamma rays are called ionizing radiation because they have enough energy to remove electrons from atoms, which can damage living cells and DNA.

• Radio waves: Broadcasting TV and radio, WiFi, Bluetooth
• Microwaves: Cooking food, mobile phones, satellite communications
• Infrared: Remote controls, thermal imaging, heating
• Visible light: Vision, photography, fiber optic communication
• Ultraviolet: Sterilization, detecting counterfeit notes, tanning
• X-rays: Medical imaging (seeing bones), airport security
• Gamma rays: Cancer treatment (radiotherapy), sterilizing equipment

Non-ionizing radiation (radio, microwave, infrared, visible) is generally safer, though microwaves and infrared can cause burns by heating tissues.

Ionizing radiation (UV, X-rays, gamma) is more dangerous:

• UV: Causes sunburn, skin cancer, cataracts
• X-rays: Damage cells, increase cancer risk (limited exposure in hospitals)
• Gamma: Most penetrating, can kill cells, cause cancer, used carefully in medicine