Refraction of light through a glass slab

Objective:

To trace the path of a light ray passing through a rectangular glass slab for different angles of incidence, measure the angles of incidence, refraction and emergence and interpret the results.

Materials Required:

Rectangular glass slab

Drawing board

White paper

Board pins

Optical pins

Protractor

Measuring scales

Pencil

Refraction through a Glass Slab -Images

 

Procedure:

Fix a white sheet of paper on a drawing board

Place the rectangular glass slab in the middle of paper and trace its boundary (ABCD) with a pen/pencil

Remove the rectangular glass slab and mark its outline properly (Rectangular ABCD)

Draw a normal (perpendicular line) NN’ at Q on the side AB of the rectangular glass slab.

Using a protractor for angle of incidence (e.g,. 30⁰, 40⁰,45⁰ & 60⁰), draw the incident ray of light PQ to the normal.

Fix two pins (P₁ and P₂) vertically along the line PQ (incident ray)

Place the rectangular glass slab back in its outline to observe the refraction and emergence.

From the other side CD observe the two pins (P₁ and P₂)through the glass slab.

Fix two more pins(P₃ and P₄) on the side CD, such that all the four pins appear in a straight line with the images of first two pins P₁ and P₂.

Remove the rectangular glass slab and mark the pins as P₃ and P₄.

Join points Q and R  to get the refracted ray and  R and S as the emergent ray.

Measure the angle of incidence (∠i) ; Angle between the incident ray of light and the normal.

Measure the angle of refraction (∠r): Angle between the refracted ray and the normal (inside the slab)

Measure the angle of emergence(∠e) : Angle between the emergent ray and the normal (on the other side)

Repeat the experiment for different angles of incidence (e.g,. 30⁰, 40⁰ 45⁰ & 60⁰) and tabulate the results.

Refraction Through a Rectangular Glass Slab: Observations and key findings

Interpretation and Conclusion:

The light ray bends towards the normal when entering the glass slab (denser medium) and away from the normal when exiting into air.

The emergent ray is parallel to the incident ray due to the slab’s parallel surface.

Lateral displacement occurs because ray shifts slightly while passing through the slab,

The experiment verifies the laws of refraction (Snell’s law) and the principle of reversibility of light.

Precautions:

Pins should be placed vertically.

Angle of incidence should be measured accurately.

The glass slab should not be moved during the experiment.

This experiment helps in understanding how light behaves when passing through different media and confirms theoretical principles of optics.

Links to this experiment

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