Question

a student wear alens of focal length 40cm and -20cm write power and nature of image​

Answer 1

Answer:

Step-by-step explanation:

f1=40cm

f2=-20cm

let the focal length in combination be f

1/f=1/f1+1/f2

1/f= 1/40+(1/-20)

1/f=1/40 -1/20

1/f= 1/40-2/40

1/f= -1/40

therefore f=-40cm

=-4/10m

power = 1/f

           = 1/-4/10

         = -10/4

        = -2.5 dioptre

hence power = -2.5D

nature of the image is real and inverted