Question
Why does a light ray incident on a rectangular glass slab immersed in any medium emerges parallel to itself? Explain using a diagram.
✓
Answer
Perform an experiment to demonstrate that light bends from its path, when it falls obliquely on the surface of a glass slab. Also show that angle of incidence is about equal to the emergent angle.
- Take a glass slab and place it on a white sheet of paper fixed on a drawing board.
- Mark the boundary ABCD of the glass slab.
- Fix two pins P1 and P2, vertically on the drawing board such that line joining the pins is inclined to the edge AB of the glass slab (Figure).
- Now, look through the glass slab from opposite side so that the images of pins P1 and P2 are seen exactly in line. Fix two pins P3 and P4, vertically on the drawing board such that pins P3, P4 and image of P1 and P2 are exactly in one line.
- Remove the glass slab and all pins. Join the points P1 and P2 with a line and extend this line to touch the edge AB at P. Similarly join the points P3 and P4 with a line and extend the line to touch the edge DC at Q.
- Join points P and Q with a straight line.
- Draw normal NN’ at P on the edge AB and a normal N1N1' at Q on the edge DC.
- Measure
Note: Distance between pins P1 and P2, and between P3 and P4 must be large.
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