Consider the following four optical arrangements intended to produce an interference pattern on a screen: (I) Two independent sodium lamps of the same wattage placed close to each other. (II) Two narrow slits illuminated by a single monochromatic laser beam. (III) Two independent laser pointers emitting light of the exact same wavelength. (IV) Light from a single narrow slit and its reflection from a plane mirror. Ho

Step-by-step solution

For a sustained interference pattern to be observed, the sources of light must be coherent, meaning they must maintain a constant phase difference with respect to time. (I) Two independent sodium lamps are incoherent sources because light is emitted by independent atoms randomly, leading to a rapidly changing phase difference. They will not produce a sustained pattern. (II) Two narrow slits illuminated by a single laser beam act as coherent sources because they are derived from the same original wavefront (Young's