Answers

2015-01-06T21:02:31+05:30
Focal length of the lens:

1. Convex lens:When rays parallel to principal axis come
from infinity and converges at a point on principal axis,that point is known as focus. The distance from optical center to the focus is known as focal length.

2.Concave lens:When rays parallel to principal axis come from infinity and diverges but tend to meet at a point on principal axis,that point is known as focus. The distance from optical center to the focus is known as focal length. 

Magnification of lens-

The ratio of the image distance and the object distance
i.e.v/u
                                    OR

the ratio of the height of image and height of object
i.e. h''/h


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