Question

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 :

The best observation is
A. I
B. II
C. III
D. IV

Answer 1

I think the third one is correct

Answer 2

When a light beam passes from one transparent medium to another the direction of its path changes, when it enters into the other medium. This phenomenon is called refraction of light.

When ray of light passing through a  rectangular glass slab the angle of emergence $\angle e$ and angle of incidence $\angle i$ will be equal.

As per the Snell’s law of refraction.The ratio of the sine of angle of incidence to the sine of angle of refraction is constant for the same colour of light and for the same pair of transparent media. Thus,

$\frac{sin{\angle{i}}}{sin{\angle{r}}} =\text{refractive index of the second medium}$

For glass slab the refractive index is =1.52

Option -1

$\frac{sin{\angle{i}}}{sin{\angle{r}}}\\\\=\frac{sin{30^{\circ}}}{sin{19^{\circ}}}\\\\=\frac{.5}{.32}=1.56$

Option-2

$\frac{sin{\angle{i}}}{sin{\angle{r}}}\\\\=\frac{sin{40^{\circ}}}{sin{28^{\circ}}}\\\\=\frac{.64}{.46}=1.39$

Option-3

$\frac{sin{\angle{i}}}{sin{\angle{r}}}\\\\=\frac{sin{50^{\circ}}}{sin{36^{\circ}}}\\\\=\frac{.76}{.58}=1.31$

Option-4

$\frac{sin{\angle{i}}}{sin{\angle{r}}}\\\\=\frac{sin{60^{\circ}}}{sin{40^{\circ}}}\\\\=\frac{.86}{.64}=1.34$

As per the result the option 1 is correct.