Q . A screen is placed 50cm from a single slit, which is illuminated with 6000Å light. If distance between the first and third minima in the diffraction pattern is 3.0 mm, then the width of the slit is
(a) 0.1 mm
(b) 0.2 mm
(c) 0.4 mm
(d) 0.8 mm
Ans: B