Introduction to Lenses

📚 Key Concepts

🔹 What is a Lens?

A lens is a piece of transparent material (usually glass or plastic) with at least one curved surface that can bend light rays.

image

Key Differences from Mirrors:

  • Transparent – light passes through them
  • We see objects through lenses, not in them
  • Can refract (bend) light rays

🔹 Types of Lenses

image

1. Convex Lens (Converging Lens)

  • Thicker at center than at edges
  • Converges light rays (brings them together)
  • Can form both real and virtual images
  • Also called converging lens

2. Concave Lens (Diverging Lens)

  • Thicker at edges than at center
  • Diverges light rays (spreads them apart)
  • Always forms virtual, erect, diminished images
  • Also called diverging lens

🔹 Simple Lens Identification

Shape Test:

  • Convex: Bulges outward in middle (like magnifying glass)
  • Concave: Curves inward at middle (thinner in center)

Water Drop Experiment:

  • Small water drop on glass acts like convex lens
  • Makes text underneath appear larger
  • Demonstrates basic lens principle

🔹 Common Applications

Convex Lenses:

  • Magnifying glasses
  • Camera lenses
  • Telescope lenses
  • Eyeglasses for farsightedness
  • Human eye lens

Concave Lenses:

  • Eyeglasses for nearsightedness
  • Peepholes in doors
  • Some camera lens systems
  • Laser beam expanders