Two Flat Glass Plates Are in Contact Along One End

Multiple Choice

Two flat glass plates are in contact along one end and are separated by a sheet of paper 3.0 × 10−⁶ m thick at the other end.The top plate is illuminated by a monochromatic light source of wavelength 490 nm.How many dark parallel bands will be evident across the top plate? (1 nm = 10−⁹ m) Note that a dark band occurs where the plates contact.

A) 13
B) 7
C) 9
D) 17