Question

An object is placed at a distance of 0.8 m from the combination of convex lens of focal length 0.4 m and a concave lens of focal length 0.5 m. Calculate the image distance.

Answer 1

Answer:

A. The Image distance for a Convex Mirror is 0.26 m.

B. The Image distance for a Concave Mirror is -1.33 m. (The value is negative which shows that the image formed will be virtual and will form beyond the pole of the mirror.

Explanation:

For a Convex lens,

u = - 0.8 m

f = + 0.4 m

Image distance (v) = 1/f = 1/v+1/u

= 1/0.4 = 1/v-1/0.8

= 2.5 = 1/v-1.25

= 3.75 = 1/v

or, 375/100 = 1/v

= 100/375 = v

= 0.26 m = v

For a Concave lens,

Assuming that the image formed is real,

u = - 0.8 m

f = - 0.5 m

1/f = 1/v+1/u

-1/0.5 = 1/v-1/0.8

-2 = 1/v-1.25

-0.75 = 1/v

or, - 75/100 = 1/v

= - 100/75 = v

= -1.33 m = v

Hope this helps.