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 are obviously bringing it on to the ‘screen’ (i.e., the retina) 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 to the diver 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?
Answers
(a) When the rays are convergent behind the mirror, boy plane mirror and convex mirror can form real images of virtual objects.
(b) the retina is working as a screen, where the rays are converging, but this screen is not at position of formed virtual image, in fact the reflected divergent rays are converged by the eye lens at the retina. thus, there is no contradiction.
(c) An observer in denser medium will observe the fishermen taller than actual height of him, due to refraction from rare to denser medium.
(d) Apparent depth decreases if viewed obliquely as compared to when observed near normally.
(e) critical angle , , the refractive index of diamond is much greater than that of ordinary glass so, critical angle of diamond (24°) is much smaller as compared to that of glass (42°).
A skilled diamond cutter thus can take the advantage of such large range of angle of incidence available for total internal reflection 24° to 90°. The diamond can be cut with so many faces, to ensure that light entering the diamond does multiple total internal reflections before coming out. this behaviour produce brilliance i.e., sparkling effect in the diamond.