Reflection and Refraction of Light

Reflection and Refraction of Light

• Light is electromagnetic radiation with wave and particle properties.
• Light travels in straight lines called rays.
• A bundle of light rays is called a beam.
• Light sources can be natural (sun, stars, fire, bioluminescence, lightning) or man-made (light bulbs, lamps, flashlights, candles, lasers).

Reflection

• Reflection is when light waves strike a surface and bounce back.
• Reflection occurs because light cannot pass through certain materials.
• Everything we see reflects light. This is how we see objects.

Types of Reflection

• Specular Reflection: Light reflects off a smooth, shiny surface (like a mirror or calm water) in a well-organized, uniform direction. This produces a clear reflection or image.
• Diffuse Reflection: Light reflects off a rough or uneven surface (like paper or a wall) in many directions. The surface is bumpy at a microscopic level, so you don't see a clear reflection; instead, you see the object itself because light spreads evenly.

Absorption and Scattering of Light

• Absorption: Light waves transfer energy to matter particles.
• Scattering: Light bounces off tiny particles (dust, air molecules, water droplets) and changes direction.

Law of Reflection of Light

• Law 1: The incident ray, the normal to the mirror at the point of incidence, and the reflected ray are in the same plane.
• Law 2: The angle of incidence (angle between incident ray and normal) equals the angle of reflection (angle between reflected ray and normal). In simpler terms: the angle at which light hits a surface equals the angle at which it bounces off.

Refraction

• Refraction: Light bends as it passes from one medium to another. This happens because light changes speed when it moves between different materials (e.g., putting a pencil in water).
• When light slows down (e.g., air to water), it bends toward the normal (an imaginary line perpendicular to the surface).
• When light speeds up (e.g., water to air), it bends away from the normal.

Dispersion

• Dispersion: The separation of light into colors by a prism. Light components refract at different angles due to their different wavelengths.
• Red light bends the least, violet the most, with other colors in between.

Index of Refraction

• Index of refraction (n): A measure of how much light slows down when it passes from one medium to another.
• The refractive index (n) is calculated by dividing the speed of light in a vacuum (c) by the speed of light in the material (v).
  • n = c / v

Snell's Law of Refraction

• Snell's Law describes how light bends when passing between different mediums.
  • n₁ sin θ₁ = n₂ sin θ₂
  • θ₁ = angle of incidence
  • θ₂ = angle of refraction
  • n₁ = refractive index of first medium, n₂ = refractive index of second medium.
  • For example, if light goes from air (n≈1) to water (n≈1.33), the constant will be about 1.33.