What is a Biconvex Lens?

• Shape: It is thicker at the center and thinner at the edges.
• Converging Action: When parallel rays of light pass through a biconvex lens, the glass refracts (bends) the light rays inward so that they all meet at a single point on the other side. This point is called the Principal Focus.
• Focal Length: A biconvex lens has a positive focal length.

In high school physics, when teachers say "convex lens", they are almost always referring to a biconvex lens. However, technically, a lens only needs one outward-curving side to be called 'convex'.

• Plano-convex: One side is flat, the other bulges out.
• Biconvex: Both sides bulge out. Both are converging lenses, but the biconvex lens bends light more strongly because refraction happens at both curved surfaces.

Depending on where the object is placed relative to the focal point (F), a biconvex lens can form different types of images:

• If the object is far away (beyond F): The image is Real and Inverted.
• If the object is very close (between the lens and F): The image is Virtual, Erect, and Magnified.

1. Magnifying Glasses: Used to read small text.
2. Microscopes and Telescopes: Used in combination with other lenses to magnify distant or microscopic objects.
3. Human Eye: The natural crystalline lens inside the human eye is a biconvex lens. It converges light onto the retina.
4. Correcting Hypermetropia: Used in spectacles to correct 'farsightedness', helping people see close objects clearly.