Question

A thin layer of colourless oil on water surface looks to be coloured in the sun light, why?

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Answer 1

When a thin film of oil spreads over the surface of water and it is seen in broad day light, brilliant colours are seen. There, colours arise due to interference of sun-light reflected from the upper and lower surfaces of the film.

Answer 2

Explanation:

The thin layer of oil looks to be coloured due to❝ \blue{\texttt{Interference}}Interference ❞. When sun light falls on the layer of oil, it is reflected from both the upper layer and lower layer of surface.

➮The path difference between the two reflected rays is given by ,

\blue{\texttt{P}}P ➭ 2μt cosθ

➮where,

u=\blue{\texttt{refractive index of layer}}refractive index of layer

t=\blue{\texttt{thickness of layer}}thickness of layer

θ = \blue{\texttt{angle of refraction}}angle of refraction

If , p ➭n (λ/ 2)

➮Where,

\textbf{n}n ➭ ➋,➍ ,➏ , ...

then layer will appear dark .

and ,if \textbf{n}n ➭ ➊,❸, ❺,➐ , ..

the layer will appear bright.

❝The colours present in the reflected light will depend on the \blue{\texttt{thickness of the layer}}thickness of the layer .❞