Question

The bluish color of water in the deep sea is due to

• A. The presence of algae and other plants found in water
• B. Reflection of sky in water
• C. Scattering of light
• D. Absorption of light by the sea

Answer 1

The correct option is C

Scattering of light

Correct options: Option C

1. The phenomenon in which the light rays deviate from their original path due to hindrances like dust particles and gas molecules is called the scattering of light. It gives rise to many optical phenomena.
2. The scattering depends on the wavelength of light. It is inversely proportional to the fourth power of wavelength, $Scattering\propto \frac{1}{{\left(Wavelength\right)}^4}$.
3. Sunlight has seven colors, that are, violet, indigo, blue, green, yellow, orange and red. Violet color scatters the most and red the least. Water molecules absorb the sunlight and scatter its colors.
4. Thus, the colors blue, indigo and violet are most scattered and the others are absorbed.
5. The scattered colors give a blue shade when observed in a large area of water that is because there is very less amount of violet in the sunlight and blue and indigo (dark blue) dominate it.
6. Thus, the water appears to be bluish in the deep sea.

Incorrect options:

Option A

1. Sea water contains algae and other plants and impurities.
2. This can cause a little difference in the color of water but does not turn it blue.
3. So, this option is incorrect.

Option B

1. Reflection is the phenomenon of throwing back light without absorbing it.
2. The color from the sky is not reflected by water but scattered.
3. So, this option is incorrect.

Option D

1. The light waves absorbed are those of higher wavelengths like red, orange, yellow, and green.
2. So, the color is not due to them but due to the light waves that are scattered.
3. So, this option is incorrect.

Hence, option C is correct.