What is principal focus?

A beam of rays adjacent and parallel to the principal axis being incident on a spherical mirror converges at a point on the principal axis (in case of concave mirror) or appears to be diverging from a point on the principal axis (in case of convex mirror) after reflection, then this point is called the … Read more

What is refractive index?

If light rays of a specific color and of a pair of specific medium refract from one medium to another medium then the ratio of sin of the incidence angle and the sin of the refraction angle is called the refractive index of the second medium with respect to the first medium for that color.