Question

What is lateral displacement in refraction? Describe an experiment to show lateral displacement in a glass slab.

Answer 1

Lateral displacement: In a glass slab lateral displacement is nothing but the perpendicular distance between the incident ray (AO) and emergent ray (BC).

Experiment to show lateral displacement in a glass slab:

Materials required: A glass slab, sheet of paper, drawing board, pencil, eight pins, protractor, set square, and a scale.

Method:

1. Fix the sheet of paper on the drawing board.
2. Place the glass slab on the paper and mark its borders and mark the corners as L, M, N, and O.(as shown below)
3. Remove glass slab and mark point B on LM and draw a perpendicular to the side LM as shown.
4. Draw a line AB making an angle of $40°$ with the normal. This is the angle of incidence at point B where light enters the glass.
5. Replace the glass slab on the marked rectangle.
6. Fix two pins at points P and Q on AB as shown in the diagram.
7. Now look through the glass slab from side NO and place a pin R along the line of sight such that pins P and Q are visible.
8. Similarly, place one more pin in line with the other three pins and mark the position as S. All the pins P, Q, R, and S should lie in a straight line
9. Remove the slab and join line RS and extend it to point C.
10. In a similar way join PQ and extend it to point B.
11. Connect BC
12. Mark AB as incident ray, BC as refracted ray, and CD as emergent ray
13. The distance or gap between emergent ray and incident ray is known as lateral displacement or d.