Question

what do you understand by the terms focus and principal focus in the context of lenses​

Answer 1

Answer:

Principal focus is a point (on the principal axis) where parallel incident rays meet after reflecting (in mirrors) or refracting (in lenses). ... Principal Focus also determines the focal length of the lens/mirror. Focus is just a random point where some rays meet, it might be at the principal focus or otherwise.

Explanation:

Answer 2

Answer:

focus : the beam of light after refraction through the lens appear to diverge . This point is called as focus .

Principal Focus : This is the point on the principal axis where all the rays coming from object parallel to principle axis are diverged or converged by lens is called principle axis .