The power of a combination of two lenses X and Y is S D. If the focal length of lens X be 1S cm :
(a) calculate the focal length of lens Y.
(b) state the nature of lens Y.
Power of combination = 5 D
Focal length of X = 15 cm= 0.15 m
Power of X = 1/ 0.15 = 6.67 D
(a) Power of Y = 5 – 6.67 = -1.67 D
f = 1/P = - 60 cm
(b) Nature of lens is Concave lens