Electromagnetic waves and visible light: Revision

1. Electromagnetic Waves

• Definition: Electromagnetic (EM) waves consist of electric and magnetic fields that are perpendicular to each other and to the direction of wave propagation.
• Speed: Travel at 3 × 10⁸ m·s⁻¹ in a vacuum.

Key Characteristics

• Higher frequency = More energy (e.g. X-rays, gamma rays).
• Lower frequency = Less energy (e.g. radio waves, microwaves).
• Shorter wavelength = Higher frequency & energy.
• Longer wavelength = Lower frequency & energy.
• Visible light is a small part of the electromagnetic spectrum.

2. The Electromagnetic Spectrum

Type of Wave	Frequency $(Hz)$	Wavelength $(m)$	Examples
Radio Waves	Lowest	Longest	Broadcasting, communication
Microwaves	Slightly higher	Slightly shorter	Cooking, radar
Infrared	Medium-low	Medium-long	Remote controls, thermal imaging
Visible Light	Medium	Medium	Human vision, photography
Ultraviolet (UV)	Medium-high	Medium-short	Sunlight, sterilisation
X-rays	High	Short	Medical imaging
Gamma Rays	Highest	Shortest	Nuclear radiation, cancer treatment

3. Visible Light

• Part of the EM spectrum that is detectable by the human eye.
• Colour variation:
  • Red = Longest wavelength, lowest energy.
  • Violet = Shortest wavelength, highest energy.

Dual Nature of Light

• Wave Nature:
  • Exhibits diffraction and interference.
• Particle Nature:
  • Interacts with matter through the photoelectric effect.

4. Key Takeaways

• EM waves differ in frequency, wavelength, and energy.
• Visible light follows a spectrum from red (low energy) to violet (high energy).
• Light behaves as both a wave and a particle.