In 1801, Thomas Young first demonstrated interference of light. His experimental set-up is shown in Fig. 14.1. As shown in Fig. 14.1, he passed sun light through a narrow pin hole ‘S’ on an opaque surface and then through two closely spaced pin holes S1 and S2 in another opaque surface. A screen ‘XY’ was arranged in front of the pin holes S1 and S2. He observed a few coloured bright and dark interference bands on the screen. To obtain a large number of clear bright and dark interference bands, the sun light in the experiment was replaced by monochromatic light and the pin holes were replaced by narrow slits.
Figure 14.1 Young’s double slit experimental set-up
Explanation of interference
The interference ...