Question

the focal length of a camera lens is 20 cm . how far away from the film must the lens be set in order to photograph an object located at a distance of 100 cm from the lens ?

Answer 1

Given: The focal length of a camera lens is 20 cm .

To find: How far away from the film must the lens be set in order to photograph an object located at a distance of 100 cm from the lens ?

Solution:

• Now we have given focal length as 20 cm, and u as 100 cm.

• We know the formula:

                 1/f = 1/v + 1/u

• So putting the values in it, we get:

                 1/20 = 1/v + 1/100

                 1/20 - 1/100 = 1/v

                 100 - 20 / 2000 = 1/v

                 80 / 2000 = 1/v

                 4/100 = 1/v

                 v = 25 cm

Answer:

               So the value of v is 25 cm.

Answer 2

Answer:

25 cm

Explanation:

f = 20 cm

u = 100 cm

v = ???

By formula ,

1/f = 1/v + 1/u

=> 1/20 = 1/v + 1/100

=> 1/20 - 1/100 = 1/v

=> 100 - 20 / 2000 = 1/v

=> 80 / 2000 = 1/v

=> 4/100 = 1/v

=> v = 100/4

=> v = 25 cm Ans...