A student is measuring the wavelength of a narrow, monochromatic light source. The double slit has a separation of 0.15 mm. A second student places markers on a screen 2.0 m in front of the slits at the positions of successive dark bands in the patterns. The student finds that the dark bands are 0.56 cm apart. a. The student has met two important conditions for interference to occur. What are they? b. Calculate the wavelength of the light source. c. Calculate the spacing of the dark bands if a source of wavelength 600.0 nm were used. (A "nm" is a nanometre, or 10 m.) . d. If a student wants the spaces between the dark bands in an interference pattern to be wider apart, should the spacing between the slits increase or decrease?