MCQ
After tracing the path of a ray of light passing through a rectangular glass slab for four different values of the angle of incidence, a student reported his observations in tabular form as given below:
S. No.$\angle\text{ i}$$\angle\text{ r}$$\angle\text{ e}$
I$30^{0}$$19^{0}$$29^{0}$
II$40^{0}$$28^{0}$$40^{0}$
III$50^{0}$$36^{0}$$50^{0}$
IV$60^{0}$$40^{0}$$59^{0}$
The best observation is:
  • A
    I
  • B
    II
  • C
    III
  • D
    IV

Answer

  1. III.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

For best results, the following conditions must be satisfied:

  1. The angle of incidence must be nearly equal to the angle of emergence.
  2. The angle of refraction must be less than the angle the incidence.​​​​​​​
  3. $\frac{\sin\text{i}}{\sin\text{r}}=1.5$ (Since, the refractive index of glass is 1.5)

Out of the 4 observations, the first observation, that is angle i = 30º; angle r = 19º and angle e = 29º is the correct observation. In this case, $\frac{\sin 30^\circ}{\sin 19^\circ}=1.535$.

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