Question

A magnifying lens has a focal length of 100 mm. An object whose size is 16 mm is placed at some distance from the lens so that an image is formed at a distance of 25 cm in front of the lens. What is the distance between the object and the lens? 

Answer 1

Given focal length (f) = 100 mm

Size of object (h) = 16 mm

Image distance (v) = −25 cm = −250 mm (negative sign because the image is on the same side as the object)

The lens formula is given by:

`1/f = 1/v - 1/u` 

`1/100 = 1/-250 - 1/u` 

`1/u = 1/100 - 1/-250` 

`1/u = 1/100 + 1/250` 

`1/u = 5/500 + 2/500` 

`1/u = 7/500` 

`u = 500/7`

u = 71.43 mm  

u = 7.143 cm

∴ The distance between the object and the lens is approximately 7.143 cm