Question

An achromatic combination of a concave and convex lenses has power 5D. If the power of convex lens is 4D, then the magnitude of focal length of concave lens is:
1)10cm 2)200cm 3)100cm 4)20cm

Answer 1

Answer:

3).100cm

As total power=5D and convex lens Power=4D.

Then rest Power=1D

As, Power=1/f(in m)

so,ATQ

1=1/f(in m)

f=1m

and,1m=100cm

i.e.,option (3)