Question

.If the power of a lens is -2.5 D, then calculate its focal length.

1 point

-20 cm

-30 cm

- 40 cm

+ 40 cm

​

Answer 1

power of lens = 1/ focal length ( in metres)

-2.5D=1/ focal length

Focal length= 1/-2.5 m

so focal length is -0.4m= -40 cm

remember power of lens is reciprocal of focal length of lens