Question

Blue colour of sea water is due to
A. Interference of sunlight reflected from the water surface
B. Scattering of sunlight by the water molecules
C. Image of sky in water
D. Refraction of sunlight

Answer 1

Hint: In order to solve this question we will use the concept as the scattering is inversely proportional to the wave length, so according to it we will try to explain our answer and we will select the correct options amongst the given options.

Complete step by step answer:

Formula used- ${\text{Scattering of light}} \propto \dfrac{1}{{{\lambda ^4}}}$
We know,
Scattering probability is inversely proportional to the wavelength or we can say scattering probability is directly proportional to $\dfrac{1}{{{\lambda ^4}}}$
Hence, smaller will be the wavelength of light higher will be its scattering.
When sunlight falls on a water molecule which acts as a prism all the seven coloured gets scattered.
As blue has smaller wavelength, therefore scattering of the blue part of the light spectrum is very large.
Also the wavelength for violet and indigo is less and they fall in the blue region but our eyes are more sensitive to blue as a whole.
Hence, the blue colour of water in the sea is due to scattering of sunlight by water molecules.
So, the correct answer is option B.

Additional information- Atoms or molecules which are exposed to light absorb light energy and re-emit light in different directions with different intensity. This phenomenon is an example of scattering, a general physical process where quanta of some form, such as light, sound, or moving particles, are forced to deviate from a straight trajectory by localized non-uniformities in the medium through which they pass. In conventional use, this also includes deviation of reflected radiation from the angle predicted by the law of reflection. Reflections of radiation that undergoes scattering are often called diffuse reflections and unscattered reflections are called specular (mirror-like) reflections.

Note- This effect can be viewed differently as water absorbs colors in the red portion of the light spectrum. Like a filter this allows for us to see shades in the blue portion of the light spectrum. The ocean will also take on green, red or other colors when light bounces off in the water from floating sediments and particles.