An object 2 cm tall stands on the principal axis of a converging lens of focal length 8 cm. Find the position, nature and size of the image formed if the object is:
(i) 12 cm from the lens
(ii) 6 cm from the lens
State one practical application each of the use of such a lens with the object in position (i) and (ii).
Converging lens is a convex lens
Focal length (f) = +8 cm
Height of the object (h) = +2
(i) Object distance (u) =-2
Lens formula is given as:
Image is at a distance of 24 cm from the convex lens; therefore, we have:
Magnification (m) =`24/-12`
Hence, the image is real and inverted.
(b) Object distance (u)=-6
According to lens formula:
Image is at a distance of 24 cm in front of the lens; therefore , we have :
Magnification` (m) =v/u `
Height of the image is 8 cm.
Here, height is positive; therefore, image is virtual and erect.
The practical application for case (1) is that it can be used as a corrective lens for a farsighted person and for case (2), it can be used as a magnifying lens for reading purposes.