Q3. In Fig. Q3, a broad beam of light of wavelength 620 nm is sent directly downward through the top plate of a pair of glass plates touching at the left end. The air between plates acts as a thin film, and an interference pattern can be seen from above the plates. Initially, a dark fringe lies at the left end, a bright fringe lies at the right end, and nine dark fringes lie between those two end fringes. The plates are then very gradually squeezed together at a constant rate to decrease the angle between them. As a result, the fringe at the right side changes between being bright to being dark every 15.0 s. (10pts) Incident light Fig. Q3 (a) Explain why the left end is always dark.(2pts) (b) At what rate is the spacing between the plates at the right end being changed? (3pts) (c) By how much has the spacing there changed when both left and right ends have a dark fringe and there are five dark fringes between them? (3pts) (d)If the two plates are away from each other at a rate of 5nm/s, at what rate the fringe at the right side changes between being bright to being dark? (1pts)The number of fringes will be larger or smaller?(1pts)