After tracing the path of rays of light through a glass slab for three different angles of incidence, a student measured the corresponding values angle of refraction r and angle of emergence e and recorded them in the table given below :
$\begin{matrix} S . N O & ∠ i & ∠ r & ∠ e I & 30^{\circ} & 20^{\circ} & 31^{\circ} I I & 40^{\circ} & 25^{\circ} & 40^{\circ} I I I & 50^{\circ} & 31^{\circ} & 49^{\circ} \end{matrix}$

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Solution

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.
$\frac{s i n i}{s i n r} = 1.5$ (since, the refractive index of glass is 1.5)
Out of the 3 observations, the first observation, that is angle $i = 30^{\circ}$ ; angle $r = 20^{\circ}$ and angle $e = 29^{\circ}$ is the correct observation.
$\frac{s i n 30^{\circ}}{s i n 20^{\circ}} = 1.46$
In the third observation $\frac{s i n 50^{\circ}}{s i n 31^{\circ}} = 1.48$

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Q. After tracing the path of rays of light through a glass slab for three different angles of incidence, a student measured the corresponding values angle of refraction r and angle of emergence e and recorded them in the table given below:

S.No.	$∠ i$	$∠ r$	$∠ e$
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II	$40^{o}$	$25^{o}$	$40^{o}$
III	$50^{o}$	$31^{o}$	$49^{o}$

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