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Ray Optics and Optical Instruments — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsRay Optics and Optical Instruments1 Mark
MCQ
A rectangular block of glass $\text{ABCD}$ has a refractive index $1.6.$ A pin is placed midway on the face $AB ($Fig$)$. 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 $AD.$
  • ✓
    Not be seen at all.
✓

Answer

Correct option: D.
Not be seen at all.
We know that, $\Box=\frac{1}{\sin\text{C}}$ Substituting $\Box=1.6$, we get $C = 38.7^\circ$ As long as angle of incidence on $AD$ of the ray emanating from pin is greater than the critical angle, the light suffers from total internal reflection and the pin cannot be seen through $AD.$

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