Question

(a) For which position of an object, a real, diminished image is formed by a convex lens?
(b) Two convex lenses A and B have focal lengths of 2.5 cm and 12.0 cm, respectively. Which lens has a greater power?
​(c) Describe with the help of a labelled ray-diagram, the formation of image when an object is placed in the front of a convex lens between focus and optical centre. State any two characteristics of the image formed.

Answer 1

(a) When an object is placed beyond '2f' of a convex lens, the image formed is diminished and real in nature.

(b) Power of a lens is indirectly proportional to its focal length. i.e. $P\propto \frac{1}{f(\mathrm{in}\mathrm{meter})}$

According to the above relation, the lens with a smaller focal length would have greater power. So, lens A has greater power.

(c)



Characteristics of the image formed above:

(i) Image is virtual
(ii) Image is erect
(iii) Image is enlarged