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.