The focal length of plano convex lens is f and its r.i 1.5.It is kept over plane glass plate.The gap between the lens and glass plate is filled by a liquid.As a result the effective focal length of the combination becomes 2f.Then the R.I of the liquid is a)1.5 b)2 c)1.25 d)1.33...and plz sir tell about sign convensions about planoconcave or convex lens...

ayusha , 7 Years ago

Grade 11