When an object is placed 8cm from a convex lens, an image is captured on a screen at 4com from the lens. Now the lens is moved along its principal axis while the object and the screen are kept fixed. Where the lens should be moved to obtain another clear?

Question

Emily Abbate · Accepted Answer

Object distance and Image distance need to be interchanged.

Common Gaussian form of lens equation is given as #1/"Object distance"+1/"Image distance"=1/"focal length"# or #1/"O"+1/"I"=1/"f"# Inserting given values we get #1/8+1/4=1/f# #=>(1+2)/8=1/f# #=>f=8/3cm# The equation now becomes as the lens is being moved. #1/"O"+1/"I"=3/8# We see that only other solution is Object distance and Image distance are interchanged. Hence, if the Object distance is made #=4cm#, clear image would be formed at #8cm#

William Audy · Answer

undefined To obtain another clear image without changing the object distance or screen distance, the lens should be moved such that the object distance and image distance remain the same. Therefore, the lens should be moved to a position where the distance from the lens to the object and the distance from the lens to the screen remain at 8 cm and 4 cm respectively.