question_answer 48)

  A rectangular block of glass ABCD has a refractive index 1.6. A pin is placed midway on   the face AB, Fig. 6(EP).4. When observed from the face AD, the pin shall (a) appear to be near A. (b) appear to be near  D. (c) appear to be at the centre of AD. (d) not be seen at all.

Answer:

  (a,d) In Fig. 6(EP).8, a pin is held at L, mid point of AB. When seen from face AD (so long as i < C) image of L appears to be at L', closer to A. From sin                 . So when angle of incidence becomes greater than C (= 387°), the rays starting from L will undergo total internal refection and pin shall not be seen at all. The choices (a) and (d) are correct