Ques 17 answer only
Q17. A biconvex lens of glass of refractive index 1.5 having focal length 20 cm is placed in a medium of retractive index 1.65. Find its focal length. What should be the value of the retractive index of the medium in which the lens should be placed so that it acts as a plane sheet of glass ?
Dear Student,
If lens put in a medium of refractive index 1.5 then it will behave like plane sheet of glass
because in that case focal length will be infinite .
Regard