Define centre of curvature of a lens.

There are many specific terms related to a lens. One of them is centre of curvature. Two spherical surfaces make up a lens, and these two spherical surfaces make up a sphere. The centre of curvature of these spheres is called the centre of curvature. It is also defined as the centre of the sphere of which reflecting surface is formed.

Define optical centre of a lens.

There are many specific terms for a lens. One of them is optic centre. When light passes through a lens, it undergoes refraction. A point on the principal axis of the lens through which a ray of light passes without deviation is called the optical centre of the lens.

Write the reason for twinkling of stars in the sky.

The earth's atmosphere is made up of several layers. Winds, temperature changes, and differing densities all have an impact. When distant light from a star passes through our turbulent atmosphere, it goes through a lot of refraction. Because some light beams reach us directly and others bend away from and towards us, when we eventually observe this light from a star, it looks to be sparkling. It occurs so quickly that it creates a twinkling effect.