a. In three to five sentences, explain why two slightly separated coherent sources of circular waves results in an alternating pattern of "bright" and "dark" bands on a screen held some reasonable distance away. Assume the two sources are coherently in phase (e.g., both are at a peak at a particular instant) at the same frequency.

b. In a double-slit interference experiment, assuming that the distance from the location of the double slit to the location of the screen remains fixed, explain what happens to the double-slit interference pattern that appears on the screen if we : (i) increase the wavelength of the laser illuminating a particular, fixed double-slit (ii) decrease the separation of the double-slit (i.e., replace the original double slit witha smaller- separation double-slit) while keeping the illumination unchanged.