A glass plate of refractive index 1.6 is in contact with an- other glass plate of refractive index 1.8 along a line such that a wedge of 0.5° is formed. Light of wavelength 5000 A 1s incident vertically on the wedge and the film is viewed from the top. Calculate the fringe spacing. The whole appa- ratus is immersed in an oil of refractive index 1.7. What will be the qualitative difference in the fringe pattern and what wll be the new fringe width?