47. light having wavelengths 6000 a and 5000 Å is incident on a fabry perot etalon. it is observed that bright fringe is obtained for both colours when the ligh

47. Light having wavelengths 6000 A and 5000 Å is incident on a Fabry Perot etalon. It is observed that bright fringe is obtained for both colours when the light passes through the etalon in the direction cos (07) to the normal and that a coincidence is next obtained in the direction cos the normal. Deduce the thickness of the air-film within the etalon. (08)to