Subject: Applied Physics 2

Topic: Interference And Diffraction Of Light

Difficulty: Medium

In the case of interference in thin film , the narrow source limits the visibility of film.

Consider ray SA starting from narrow source ‘S’. It suffers reflection and enters the eye whereas SB incident at a different angle after reflection and internal reflection will not reach the eye. Hence only limited portion of the film is visible. If an extended source of light is used, then S1 A and S2A after reflection and internal reflection will reach the eye from a large portion of film.