Question

Q86. A thin layer of colour less oil having refractive index 1.4 is spread over water in a
container. If the light of wavelength 6400 Aº is absent in the reflected light, what is the
minimum thickness of the oil layer?
A. 2100 Armstrong
B. 1900 A
C. 2285 Aº
D. 100 A
​

Answer 1

Answer:

2285

Explanation:

2×refractive index×thickness= n× wave length

=>t=n×lambda/(r.i×2)

==>t= lambda/(r.i×2)

=>t= 2285Å

Answer 2

The thickness of the oil layer is 228.5 nm.

Step-by-step process

Given:

The refractive index of oil = 1.4

The light's wavelength = 6400 A° = 640 nm

To find = The minimum thickness of the layer of oil

Solution:

Let the thickness of the layer of oil be t

Using the formula to calculate the minimum thickness of oil:

2 ×μt ×cosr = nλ

Here, μ = refractive index

r= 0

n= number of layers;

λ = wavelength

Plugging the values in the equation, we get:

2× 1.4 ×t cos0 = 1× 640

2.8×t = 640

t = 228.5 nm

Result:

Therefore, the thickness(t) of the oil layer is 228.5 nm.

(#SPJ3)