what is the difference between focus and principal focus?
 

Asked by s.bedi2005 | 27th Nov, 2015, 08:28: PM

Expert Answer:

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.

Answered by Romal Bhansali | 28th Nov, 2015, 07:57: PM

Queries asked on Sunday & after 7pm from Monday to Saturday will be answered after 12pm the next working day.