Two flat glass plates are in contact along one end and are separated by a sheet of tissue paper at the other end.A monochromatic source of wavelength 427 nm illuminates the top plate.If 11 dark bands are counted across the top plate,what is the paper thickness? (1 nm = 10−⁹ m) A)4.3E-6 m B)1.7E-6 m C)2.1E-6 m D)2.6E-6 m E)1.3E-6 m

Question

Quizplus · Accepted Answer

The number of dark bands is given by the formula:

n = (2t(m-1) + X)/λ

where
t = thickness of tissue paper
m = order of the dark band
X = distance from the central maxima to the mth dark band
λ = wavelength of light

Since there are 11 dark bands and the first one is at m = 1, then the distance from the central maxima to the first dark band is X = λ/2.

Substituting these values in the formula and solving for t, we get:

t = (nλ - X)/2(m-1)
  = (11 x 427 nm - 213.5 nm)/(2 x 10)
  = 2.14E-6 m

Converting to scientific notation with only one significant figure, we get:

t = 2.1E-6 m

Therefore, the best choice is (C).

Two Flat Glass Plates Are in Contact Along One End