Question

Define main focus of convex lens.

Answer 1

Hint: Focus means where the light focuses. Light gets converged when it gets refracted from the surface of the convex lens whereas it gets diverged when it is refracted from the surface of the concave lens. When parallel rays pass through a convex lens it converges and meets at a point called the focus. Intensity at that point will always be maximum. Focus mainly denoted as F.

Complete step by step answer:
Main focus:
When light rays parallel to the principal axis coming from infinity fall on the surface of the convex lens, it converges at a single point on the principal axis. This point is called the ‘Main Focus of the convex lens. The main focus is also referred to as simply focus or focal point or principle focus. A convex lens has two foci.

Additional Information:
There are two main types of lenses, the convex lens, and the concave lens. A convex lens is thicker at the center and thinner at the edges whereas the concave lens is thinner at the center and thicker at the edges. The distance between the main focus and the center of the lens is called the focal length of the lens. The focal length is half of the radius of the curvature of the lens. Since a convex lens converges light falling in it, it is also called a converging lens. When the object is at infinity i.e. very far from the lens then the image is formed at the focus which is real, inverted, and diminished. And when the object is at the focal point, a real, inverted, and magnified image is formed at infinity.
Note:
Do not get confused between these two types of lenses. Many times students get confused between convex and concave lens especially about their shapes. A simple way to remember their shapes is to remember their applications. It is easy to visualize their shapes once you understood their principle of working.