CHAPTER 11: THIN LENSES

Lenses are transparent objects (usually glass or plastic) that refract light rays to form images. They are the foundation of vision correction, microscopes, telescopes, and cameras. Understanding lenses means understanding how light bends to create the images we see. This chapter will give you mastery over converging and diverging lenses, the mathematics of image formation, the human eye, and the instruments that extend our vision.

11.1 TYPES OF LENSES

Lenses are broadly classified by their shape and how they affect parallel light rays.

11.1.1 Converging Lenses (Convex Lenses)

• Shape: Thicker at the centre than at the edges.
• Action on parallel light: Bends (converges) light rays towards a common point.
• Types of convex lenses:
  • Biconvex: Both surfaces curved outward.
  • Plano-convex: One flat surface, one curved outward.
  • Convex meniscus: One surface convex, one concave, but centre is thicker than edges.
• Uses: Correcting hypermetropia (farsightedness), magnifying glasses, camera lenses, microscope objectives.

11.1.2 Diverging Lenses (Concave Lenses)

• Shape: Thinner at the centre than at the edges.
• Action on parallel light: Bends (diverges) light rays outward, making them appear to come from a common point in front of the lens.
• Types of concave lenses: