Wave Theory of Light and Optics Summary

Fundamentals of Optics and Light Models

• Definition: Optics is the physics branch studying light properties and behaviors.

• History and Propagation: Around $300 \, BC$, mathematicians like Euclid claimed light travels in a straight line. Light travels straight until it encounters a different medium, where it can reflect, refract, or be absorbed.

• Dual Models of Light:

  • Wave model: Describes propagation via wavelength and frequency; explains color.

  • Particle model: Describes interactions with atoms; light consists of photons (energy particles), explaining lasers and matter interaction.

Properties of Light Waves

• Wave Nature: Light is a disturbance carrying energy through an electromagnetic field. Unlike sound (pressure), light does not require a physical medium and can travel through a vacuum.

• Speed of Light ($c$): In a vacuum, $c = 300 \, 000 \, 000 \, m/s$. Light slows in denser media like glass.

• Frequency ($f$): Measured in Hertz ($Hz$) or $1/s$. It is the number of crests passing a point per second.

• Relationship: As frequency increases, wavelength decreases.

The Electromagnetic Spectrum (EMS)

• Scope: Visible light represents only $0.0035\%$ of the total EMS. Other bands include Radio waves, microwaves, infrared radiation, ultraviolet, X-rays, and Gamma rays.

• The Visible Spectrum:

  • Violet: Shortest wavelength ($380-440 \, nm$).

  • Blue: $440-485 \, nm$.

  • Cyan: $485-510 \, nm$.

  • Green: $510-565 \, nm$.

  • Yellow: $565-590 \, nm$.

  • Orange: $590-625 \, nm$.

  • Red: Longest wavelength ($625-740 \, nm$).

Color Theory and Interaction with Matter

• White Light: The sum of all visible wavelengths; can be split using a prism or combined using primary colors.

• Primary Colors of Physics: Red, Blue, and Green.

• Secondary Colors:

  • $\text{Red} + \text{Blue} = \text{Magenta}$

  • $\text{Blue} + \text{Green} = \text{Cyan}$

  • $\text{Red} + \text{Green} = \text{Yellow}$

• Absorption and Reflection: Objects appear a specific color based on the frequencies they reflect. Black surfaces absorb all colors (converting energy to thermal energy), while white surfaces reflect all colors.

Mechanisms of Light Production

• Chemiluminescence: Light from chemical reactions (e.g., Glowsticks).

• Bioluminescence: Light from living organisms (e.g., Fireflies).

• Electroluminescence: Light from electron flow (e.g., LEDs).

• Fluorescence: Immediate emission of visible light after absorbing UV radiation.

• Phosphorescence: Slow release of absorbed energy as light (e.g., Glow-in-the-dark materials).

• Incandescence: Light produced by heating a solid until it radiates (e.g., Iron bar, incandescent bulb filament).

Reflection and Image Characteristics

• Law of Reflection: The angle of incidence equals the angle of reflection on flat surfaces/plane mirrors.

• Virtual Image: An image formed where the eye perceives light to originate (e.g., behind a mirror); it cannot be projected onto a screen.

• Image Properties (SALT):

  • Size: Larger, smaller, or same size as object.

  • Attitude: Upright or inverted.

  • Location: In front of or behind the mirror.

  • Type: Real (in front of mirror) or Virtual (behind mirror).