The distance between the optical centre of a convex lens and its principal focus is called its ?

A convex lens is a lens that is thicker at the center than at the edges and converges light rays that pass through it. One of the key properties of a convex lens is its focal length, which is defined as the distance between the optical centre of the lens and its principal focus. The principal focus is the point where parallel rays of light, after passing through the lens, converge.

The optical centre of a lens is a point within the lens where light passes without any deviation. The focal length determines how strongly the lens converges or diverges light. A shorter focal length means the lens bends light more sharply and brings it to focus at a closer distance, while a longer focal length bends light more gently.

The focal length is different from other properties of a lens:

• 
  

  Radius of curvature refers to the radius of the spherical surfaces of the lens.

  
  


• 
  

  Power of a lens is the reciprocal of the focal length (measured in meters) and indicates its ability to converge or diverge light.

  
  


• 
  

  Magnification is the ratio of the image height to object height formed by the lens.

  
  

Convex lenses are widely used in magnifying glasses, cameras, microscopes, and telescopes. Understanding the focal length is essential for designing these optical devices, as it directly affects image formation, clarity, and magnification.

In physics, focal length is a fundamental concept in geometrical optics and helps students calculate image distance, magnification, and lens power using lens formulas. Studying the focal length and its effects allows learners to connect theoretical optics principles with real-life applications, such as eyeglasses, projectors, and optical instruments.