Question

the convergent lens of power 8d is combined with a divergent lens of power -10d calculate

1.power of combination
2.focal length of combination

Answer 1

1 power of combination

8 +(-10)

= -2D

2 focal length of the combination

p=1/f

-2=1/f

f=-0.5

Answer 2

>>>>now as they are placed in contact (combined) we can find the power of lens combination by the algebraic sum of powers of individual lens..

thus power of combination of lens will be -

8+(-10)

=-2 D

therefore focal length will be = 1/-2

= - 0.5m or - 500cm

Hope helped.