Question

Two lenses of power + 2.5 D and -3.75 D are combined to form a compound lens its focal length
will be
a) 40
b)-40.
c) 80
d) -80​

Answer 1

Answer:

-40..............................

Answer 2

Answer:

(d) -80

Explanation:

P = P1 + P2

P = +2.5 +( - ) 3.75

P = -1.25

f = 100/P ( in cms )

f = 100/-1.25

f = -80