🟩 INTRODUCTION

Light is a form of electromagnetic radiation that allows us to see objects and understand the physical world. It travels in straight lines, moves at a speed of approximately 3.0 × 10⁸ m/s in vacuum, and interacts with matter through reflection, refraction, absorption, and transmission.

Light shows dual behavior. In some situations it behaves as a wave, and in other situations it behaves as a particle. This is known as the wave–particle duality of light.

Understanding light is essential in the development of modern technologies such as cameras, eyeglasses, microscopes, telescopes, fiber-optic communication, and solar panels.

🟦 BASIC PROPERTIES OF LIGHT

• Travels in straight lines in a uniform medium
  
  

• Does not require a material medium
  
  

• Has very high speed in vacuum
  
  

• Can be reflected and refracted
  
  

• Can transfer energy

🟪 WAVE MODEL OF LIGHT

The wave model describes light as an electromagnetic wave.

Key Ideas:

• Light consists of oscillating electric and magnetic fields
  
  

• It can travel through empty space
  
  

• It has wavelength and frequency
  
  

• Its speed changes when entering a different medium
  
  

Phenomena explained by the wave model:

• Reflection
  
  

• Refraction
  
  

• Diffraction
  
  

• Interference

🟨 REFLECTION OF LIGHT

Reflection is the bouncing of light from a surface.

Law of Reflection:

Angle of incidence = Angle of reflection

Types of Reflection:

Regular reflection – occurs on smooth surfaces; forms clear images
Diffuse reflection – occurs on rough surfaces; scattered light

Examples:

• Plane mirrors
  
  

• Calm water surfaces
  
  

• Periscopes

🟩 REFRACTION OF LIGHT

Refraction is the bending of light when it passes from one medium to another due to a change in speed.

Key Concepts:

• Light slows down in denser media
  
  

• Light speeds up in less dense media
  
  

• Bending occurs at the boundary
  
  

Snell’s Law:

n₁sinθ₁ = n₂sinθ₂

Examples:

• Bent appearance of a straw in water
  
  

• Lenses forming images
  
  

• Rainbows

🟦 PARTICLE MODEL OF LIGHT

The particle model describes light as a stream of photons.

A photon is a packet of energy with no mass and no electric charge.

Key Ideas:

• Energy of a photon depends on its frequency
  
  

• Light transfers energy in discrete amounts
  
  

• Light can eject electrons from metal surfaces
  
  

Phenomenon explained:

Photoelectric effect

This shows that light behaves as a particle because energy is delivered in fixed quantities.

🟨 APPLICATIONS OF LIGHT

Mirrors

• Periscopes
  
  

• Reflecting telescopes
  
  

• Security mirrors
  
  

Lenses

• Eyeglasses
  
  

• Microscopes
  
  

• Cameras
  
  

• Projectors
  
  

Fiber Optics

• Internet communication
  
  

• Medical endoscopy
  
  

Solar Cells

• Convert light energy into electrical energy
  
  

Natural Phenomena

• Rainbows
  
  

• Halos
  
  

• Mirage

🟥 SUMMARY

• Light is an electromagnetic wave and a particle.
  
  

• Wave model explains reflection, refraction, diffraction, and interference.
  
  

• Particle model explains the photoelectric effect and energy transfer.
  
  

• Modern technology depends on the behavior of light.