Question

Answer the following questions:

(a) You have learnt that plane and convex mirrors produce virtual images of objects. Can they produce real images 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?

Answer 1

(a) A plane or convex mirror can produce a real image if the object is virtual: When the rays incident on a plane or a convex mirror are converging to a point behind the mirror they are reflected to a point in front of the mirror on a screen. 

(b) There is no contradiction. The convex lens of the eye produces a real image of virtual object. The Virtual image acts as an object for the eye lens. 

(c) The fisherman looks taller to the diver because the ray of light coming from the fisherman (in air) travels from the rarer to denser medium and hence it bends towards to come from a larger distance and hence the fisherman looks taller. 

(d) The apparent depth decreases when tank of water is viewed obliquely compared to the apparent depth when seen normally. 

(e) Refractive index of a diamond (about 2.4) is much larger than that of glass (about 1.5). As, sini_c = 1µ, the critical angle of diamond is about 24°. A diamond cutter shapes the faces of diamond such that for the angles of incidence in the range of 24° to 90°, the light entering the diamond suffers TIR from many faces before getting out and hence produces a sparkling effect.