Engineering Physics

14.2 Young’s double slit experiment

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 ...