Types of Lenses §

Lenses are optical devices made of transparent material such as glass or plastic, used to converge or diverge light. They are essential in various applications, including cameras, microscopes, glasses, and telescopes. The behaviour and use of a lens are largely determined by its shape and material.

Classification of Lenses §

Lenses are broadly classified into two main categories based on their shape and the way they bend light:

1. Convex Lenses (Converging Lenses) §

• Shape: Convex lenses are thicker at the center than at the edges.
• Function: They converge (bring together) light rays. When parallel rays of light pass through a convex lens, they are brought to a point called the focal point.
• Types:
  • Biconvex: Both surfaces are outward-curved.
  • Plano-Convex: One flat surface and one convex surface.
  • Concavo-Convex: One concave and one convex surface, but the convex curvature is greater than the concave curvature.

2. Concave Lenses (Diverging Lenses) §

• Shape: Concave lenses are thinner at the center and thicker at the edges.
• Function: They diverge (spread out) light rays. Parallel rays of light after passing through a concave lens appear to come from a single point called the focal point.
• Types:
  • Biconcave: Both surfaces are inward-curved.
  • Plano-Concave: One flat surface and one concave surface.
  • Convexo-Concave: One convex and one concave surface, but the concave curvature is greater than the convex curvature.

Applications of Lenses §

• Convex Lenses: Used in magnifying glasses, eyeglasses for farsightedness, cameras, and telescopes.
• Concave Lenses: Used in eyeglasses for near-sightedness, peepholes, and certain types of cameras.

Physics Behind Lenses §

The behaviour of light as it passes through lenses is governed by the principles of refraction. The bending of light in different lenses can be explained using Snell’s Law and the concept of the refractive index.

Test Questions §

1. STARTI [Basic] Question: What is the difference in shape between convex and concave lenses? Back: Convex lenses are thicker at the center than at the edges, while concave lenses are thinner at the center and thicker at the edges. ENDI
2. STARTI [Basic] Question: How do convex lenses affect light rays? Back: Convex lenses converge (bring together) light rays to a focal point. ENDI
3. STARTI [Basic] Question: For what purpose are concave lenses typically used? Back: Concave lenses are used to diverge light rays and are typically used in eyeglasses for near-sightedness and in peepholes. ENDI