Question

While performing the experiment on tracing the path of a ray of light through a rectangular glass slab, in which of the following experimental set-ups is a student like to get the best results?
\[{P_1}\] and \[{P_2}\] are the positions of pins fixed by him:

Answer 1

Hint:We get the refracted ray while looking for the pins to align in a straight line, through the other side of the glass slab. Pins placed close to each other will prevent us from matching the path of the light in between the pins.

Complete answer:
In the given question, we are supplied with the following data:
There is a glass slab lying flat on a plane surface. A student doing an experiment on the refraction of light through a glass slab by placing the pins in different positions in four ways, as shown in the above figures. We are asked to find the correct way of placing the pins in order to get the best results.

To begin with, to get the best result, the student must clearly observe the light rays after refraction, from the other side of the glass slab. In the first and the fourth image, we can see that the pins are placed close to each other. The pins must not be too close to each other because, as viewed from the other side of the slab, it would be impossible to match the light going between them both. So, we have to reject the images first and fourth.

Again, after emergence from the other side of the slab, the angle of incidence and the distance of the point of incidence from the centre slab must be ideal for observing the shifted light direction. But in image number three, there are no such errors in there. It is free from all the errors. The pins are not close to each other and the angle of incidence and the distance of the point of incidence from the centre slab are also ideal for observing the shifted light direction.Hence, the correct set-up is image number three.

The correct option is III.

Note: While answering this question, most of the students tend to make mistakes by choosing image number two, which is wrong, because the point of incidence is located near the midpoint of the glass slab. It is incorrect to place the pins away from each, because in that way one can clearly get the correct path of the refracted ray.