Refraction Through a Rectangular Glass Slab

Aim

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

Materials Required

Procedure

1. Fix a sheet of white paper on a drawing board using drawing pins.
2. Place a rectangular glass slab over the sheet in the middle.
3. Draw the outline of the slab with a pencil. Let us name the outline as ABCD.
4. Take a point E on the line AB and draw a normal EN to it.
5. Draw a line PQ at an angle to the normal. This is the incident ray.
6. Fix two pins, P1 and P2, vertically on the line PQ.
7. Look for the images of the pins P1 and P2 through the opposite face CD.
8. Fix two other pins, P3 and P4, such that these pins and the images of P1 and P2 lie on a straight line.
9. Remove the pins and the slab.
10. Join the positions of P3 and P4 to meet line CD at F. This is the emergent ray.
11. Join points E and F inside the outline. This represents the refracted ray.
12. Measure the angle of incidence, angle of refraction, and angle of emergence.
13. Observe the lateral displacement of the emergent ray.

Precautions

• The pins should be fixed vertically.
• The glass slab should have clean edges and should not be moved once the outline is drawn.
• The distance between the pins should be at least 5 cm for better accuracy.
• Draw normals accurately using a protractor.