A ray of light from a monochromatic point source of light is incident at a point on the screen. If a thin mica film of thickeness 't' and refractive index 'n' is introduced in its path, then the optical path

Step-by-step solution

Let the original geometric path length be x . Before the introduction of the mica film, the optical path is x (assuming the medium is air or vacuum with refractive index 1 ). When a mica film of thickness t and refractive index n is introduced, the light travels a distance x - t in air and a distance t in the mica film. The new optical path is (x - t) 1 + t n = x + (n - 1)t . The change in the optical path is (x + (n - 1)t) - x = (n - 1)t . Thus, the optical path is increased by (n - 1)t . Answer: is increased by (