Michelson interferometer is mainly used to measure the wavelength of a given light wave in college physics experiments, mainly using the equal inclination interference of light. On the basis of equal inclination interference, Michelson interferometer can also be used to observe the equal thickness interference of light. When the interference thickness is equal, the optical path difference between the two beams is 0. Adding transparent medium to one of the optical paths changes the refractive index of light at this position, thus changing the optical path and causing the change of optical path difference. This principle can be used to measure the refractive index of transparent media.
This experiment mainly uses the phenomenon that white interference fringes appear on the receiving screen when the optical path difference e=0, and the change of the position of the movable mirror when the white fringes are called out after placing the plastic sheet, and obtains the change of the optical path difference caused by the piece to be measured, so as to calculate the refractive index n of the piece to be measured.