Review Excited potassium atoms emit deep-violet light at wavelengths 404.4 nm and 404.7 nm. Suppose light from a potassium lamp passes through a diffraction grating that has 680 slits per millimeter. Part A How far behind the grating must a viewing screen be placed so that the two first-order fringes are separated by 1.0 mm? Express your answer with the appropriate units. μΑ ? L = Value Units