Two beam interference experiment is performed using a laser beam. The intensity of twobeams is equal, that is. E1 E2. The intensity ratio between bright and dark lines is 0.2, that is, Imin/max = 0.2. Find the degreeof partial coherence, or fringe visibility. (2) In Q3-(1), when the path distance between two beam paths is 10 cm, find the coherence length of the laser beam. (Hint, the degree of partial coherence is linearly dependent on the beam path distance.)