A rectangular block of glass ABCD has a refractive index of 1.6. A pin is placed midway on the face AB as shown in the figure. When observed from the face AD, the pin shall:
1. appear to be near A
2. appear to be near D
3. appear to be at all the centre of AD
4. not be seen at all
(4) Hint: It depends on the critical angle of incidence whether the pin is seen through AD or not.
Step 1: Find the critical angle.
For = 1.6, the critical angle, = 1/sinC, we have C= 38.7.
Step 2: Find if the pin is visible through AD.
When viewed from AD, as long as the angle of incidence on AD of the ray emanating from the pin is greater than the critical angle, the light suffers total internal reflection and cannot be seen through AD.
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