Magicians are doing magical events on some scientific facts. A magician during a show makes a convex lens with refractive index 1.47 which disappears in a trough of liquid of refractive index1.47. What is the nature of the lens in the liquid?

a)Convex Lens, b) Concave Lens, c) Plain Glass Sheet d) Byconvex lens

well this is a funny question actualyl according to lens makers formula if u2=u1 thats is medium and lens refractive index will   be same in the formula their will give 1 ans a result -1 =0 so of course if 1/f=0 then f=inf and if f=inf then r=inf and that is the property of a plane glass sheetso ans is C

Plain Glass Sheet. This is a famous forensic test.