A student investigates the interference of light in a Young’s double slit experiment.

i). Explain why there is no interference pattern if the two slits are 5.0 cm apart.
ii). Explain why it is better for the student to observe the interference patterns at a distance of about 1.0 m from the slits.

b) A beam of light of wavelength 589 nm is directed at the double-slit to produce an interference pattern on a screen placed 120 cm from the slits.The distance between 20 bright fringes is 4.8 mm.Calculate the separation between the slits.