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 490 nm illuminates the top plate.If 21 dark bands are counted across the top plate,what is the paper thickness? (1 nm = 10^-9 m) A)2.7 x 10^-6m B)3.4 x 10^-6 m C)4.9 x 10^-6 m D)5.8 x 10^-6 m

Question

Quizplus · Accepted Answer

The thickness of the tissue paper can be found using the formula 
t = (m + 1/2) λ/2n
where t is the thickness of the tissue paper, λ is the wavelength of light, n is the refractive index of tissue paper, and m is the number of dark fringes observed.

Here, λ = 490 nm and m = 21.
The refractive index of tissue paper is not given, but it is assumed to be close to that of air, which is 1.

Substituting the values in the formula, we get
t = (21 + 1/2) × 490 × 10^-9 /(4 × 10^-6)
t = 4.9 × 10^-6 m
Converting to scientific notation and rounding off to two significant figures, we get
t = 4.9 × 10^-6 m = 4.9 μm = 4.9 x 10^-3 mm
 
Therefore, the best choice is C, which is 4.9 x 10^-6 m in scientific notation.

Two Flat Glass Plates Are in Contact Along One End