Question

Write the difference between principal focus and focus of lens​

Answer 1

Answer:

Explanation:

• When rays of light are incident on a lens or a mirror, they refract/reflect to a certain point on the principal axis. This point is called the focus of the lens/mirror.

• This point can be anywhere on the principal axis, depending on how the rays are initially travelling.

 

• Principal focus is a special case of focus wherein the rays are travelling parallel to the lens/mirror and then refract/reflect to a particular point on the axis.

• Generally the rays are parallel if the object is at infinity.

Answer 2

Answer:

Principal focus is a point on the principal axis where the rays which are incident parallel to the principal axis meet after reflection. ... Focus is a point where rays parallel to each other meet. It is not necessary for the rays to be parallel to the principal axis.