Draw a ray diagram of an image formed when an object kept at a distance of 50 cm from a convex lens having focal length 20 cm. Write any two nature of image. Calculate the power of lens.

Solution:

Given
Focal length, f = 20 cm
Object distance, u = 50 cm
Let, image distance be v
From lens formula 

Hence from these above calculations we obtained that the image is formed on the opposite side of the lense in which the object is placed. Magnification, m = 0.667 reveals that image form is real and inverted and smaller in size than the object.

Ray diagram is drawn below:-

From the above ray diagram nature of image can be noticed:-
(i)    Real

(ii)   Inverted

(iii)  Diminished

Power of the lens, P = 1/f = 1/20 cm = 0.05 dioptre.