Question

Answer the following questions :
(a) You have learnt that plane and convex mirrors produce virtual images of objects. Can they produce real images under some circumstances ? Explain.
(b) A virtual image, we always say, cannot be caught on a screen. Yet when we see a virtual image, we bring it to screen i.e. retine of our eye. Is there a contradiction ?
( c) A diver under water looks obliquely at a fisherman standing on the bank of a lake. Would the fisherman look taller or shorter than what he actually is ?
(d) Does the apparent depth of a tank of water change if viewed obliquely ? If so, does the apparent depth increase or decrease ?
( e) The refractive index of diamond is much greater than that of ordinary glass. Is this fact of some use to a diamond cutter ?

Answer 1

(a) Yes, when rays incident on a plane or a mirror are tending to converge to a point behind the mirror, they are reflected to a point on a screen in front of the mirror. Hence a real image is formed (when the object is virtual).
(b) No, there is no contradiction. Eye lens is convergent. It forms a real image of the virtual object (i.e., the virtual image being seen) on the retina.
( c) As fisherman is in air, light travels from rarer to denser medium. It bends towards the normal, appearing to come from a larger distance. Therefore, to the diver under water, fisherman looks taller.
(d) Yes, the apparent depth decreases further, when water tank is viewed obliquely compared to the depth when seen near normally.
As `mu = (1)/(sin C) :. sin C = (1)/(mu)`
As refractive index of diamond is much greater than that of ordinary glass, critical angle `C` for diamond is much smaller `(~~ 24^@)` as compared to that for glass `(~~42^@)`. A skilled diamond cutter exploits the large range of angles of incidence of light `(24^@` to `90^@)` to ensure that light entering the diamond suffers multiple total internal reflections within the diamond. This produces sparkling effect in the diamond.