Question

We combine two lenses, one is convex and other concave having focal lengths f1 and the other f2 and their combined focal length is F. Combination will behave as concave lens if
a) f1>f2
b) f1=f2
c) f1 d) 6.5 D
Please answer with reasoning.

Answer 1

at first u have to calculate power by formula 1/f

then you have to add both the powers

if total is negative then it will behave as a concave lens.

No if power is 6.5 dioptre then it will behave as a convex lens