a convex lens of power `+6` diopter is placed in contact with a concave lens of power`-4` diopter. What will be the nature and focal length of this combination?

Options

A. Concave, `25 cm`
B. Convex, `50cm`
C. Concave, `20cm`
D. Convex, `100cm`

Answer

B

Explanation

Power of combination `=(6-4)D=2D`
Power `=(100)/("f in cm")`
`2=(100)/(f) i n cm`
or `f` in `cm =50`
Since the net power is positive therefore the combination shall behave like a convex lens.