Question

Many cells are transparent and colorless. Structures of great interest in biology and medicine can be practically invisible to ordinary microscopy. An interference microscope reveals a difference in refractive index as a shift in interference fringes to indicate the size and shape of cell structures.The idea is exemplified in the following problem: An air wedge is formed between two glass plates in contact along one edge and slightly separated at the opposite edge. When the plates are illuminated with monochromatic light from above, the reflected light has 65 dark fringes. (a) What is the thickness of the gap if 580 nm light is used? An air wedge is formed between two glass plates in contact along one edge and slightly separated at the opposite edge. When the plates are illuminated with monochromatic light from above, the reflected light has 65 dark fringes. (b) Calculate the number of dark fringes that appear if water (n = 1.33) replaces the air between the plates. (Keep in mind that the is the number of frindges, so your value should be an integer.)

Answer 1

Here we apply thin film interference concept. First we find net path difference between two reflected rays and then apply condition for interference minimum.