Properties of Light and Electromagnetic Waves

Properties of Light

• Light is made up of photons
  • Photons are massless packets of energy that travel at the speed of light.
  • Speed of light in a vacuum: $300,000,000 ext{ m/s}$ (or $300,000 ext{ km/s}$)

Behavior of Light

• Light behaves both as a stream of particles (photons) and as a wave.
  • In a vacuum, light travels in straight lines.

Luminous vs. Non-Luminous Objects

• Luminous Objects: Emit their own light (e.g., the Sun, lightbulbs).
• Non-Luminous Objects: Do not emit light, instead reflect light (e.g., the Moon, books).

Interaction of Light with Materials

When light hits a material, it can:

1. Transmission: Light passes through (e.g., clear glass).
2. Specular Reflection: Light reflects in a single direction (e.g., mirrors).
3. Diffuse Scattering: Light reflects in multiple directions (e.g., rough surfaces).
4. Absorption: Material absorbs light (e.g., black surfaces).

Properties of Waves

• Wavelength ($\lambda$): The distance between successive crests of a wave.
• Frequency ($f$): The number of oscillations per second.
• Time Period ($T$): Time taken for one complete oscillation.
• Amplitude: Maximum displacement from equilibrium.

Measuring the Speed of Light

• Early measurement attempts by Galileo and his apprentice showed light as faster than sound.
• Fizeau & Foucault measured it in the 1800s to be approximately $300,000 ext{ km/s}$.

Wavelength and Frequency Relations

• Wave speed equation: $c = f \lambda$ where:
  • $c$ = speed of light (constant at $300,000 ext{ km/s}$)
  • $f$ = frequency
  • $\lambda$ = wavelength

The Electromagnetic Spectrum

• Visible light is a small part of the electromagnetic spectrum.
  • Ranges from gamma rays (shortest wavelength) to radio waves (longest wavelength).
• Atmospheric Windows: Only visible light, radio, and some infrared light reach the ground.

Scattering of Light

• Blue light is scattered more than red light, resulting in a blue sky.
• At sunset, the longer path through the atmosphere scatters blue light, making the sun appear red.

Reflection of Light

• Reflection occurs when light bounces off a surface.
• Key terms:
  • Incident Ray: Incoming light.
  • Reflected Ray: Light that bounces off.
  • Normal Line: Perpendicular to the surface at the point of incidence.
  • Angle of Incidence = Angle of Reflection.

Vision and Light

• The eye focuses light using the cornea and lens on the retina, which sends signals to the brain.
• White light can be separated into the seven colors of the rainbow using a prism.

Color and Light

• Colors perceived depend on wavelengths reflected by objects.
• Primary colors of light: Red, Green, Blue.
  • Combine to create secondary colors:
  • Red + Green = Yellow
  • Red + Blue = Magenta
  • Green + Blue = Cyan

Using Filters and Lighting

• Filters can block certain colors and allow others to pass.
• A white object reflects all colors, while colored objects reflect specific wavelengths.
• Observing colors under different colored lights changes appearance (e.g., red shorts appear black under blue light).

Conclusion

• Understanding light's properties, behavior, and interaction with matter is crucial for various applications in science and technology, ranging from optics to astronomy.