Q16
3 marksShort AnswerSection A

State the difference in colours of the sun observed during sunrise/sunset and noon. Give explanation for each.

The Human Eye and the Colourful World
Scattering of Light
Official Answer

Difference in Colours:

  • At Sunrise and Sunset: The Sun and the surrounding sky appear reddish.
  • At Noon: The Sun appears white (with very little yellow/blue scattering).

Explanation:

  1. At Sunrise and Sunset:
  • The Sun is near the horizon, and the sunlight has to travel a longer distance through thicker layers of the Earth's atmosphere before reaching our eyes.
  • During this long journey, most of the shorter wavelengths (blue and violet light) are scattered away by the minute particles in the atmosphere.
  • Consequently, only the least scattered longer wavelengths (primarily red light) reach our eyes, making the Sun appear reddish.

  1. At Noon:
  • The Sun is directly overhead, and the light travels a relatively shorter distance through the atmosphere.
  • Because of this shorter path, only a very small fraction of the blue and violet light is scattered.
  • Since almost all the component colours reach our eyes together with minimal scattering, the Sun appears white.
reddishwhitelonger distanceshorter distancescatteringshorter wavelengthslonger wavelengths

Marking Scheme

  • 11 mark
  • 21 mark
  • 31 mark

Hint

Think about how the distance travelled by sunlight through the atmosphere changes from noon to sunset, and how this affects the scattering of shorter wavelengths versus longer wavelengths.

Quick Oral Answer

At sunrise and sunset, the Sun appears red because light travels a longer distance through the atmosphere, scattering away the blue light and leaving only the red light to reach our eyes. At noon, the path is short, scattering is minimal, so the Sun appears white.

Analysis & Explanation

The phenomenon of the changing colour of the Sun is a direct consequence of the scattering of light by the Earth's atmosphere. According to the principles of scattering, smaller particles in the atmosphere scatter shorter wavelengths (blue/violet) much more effectively than longer wavelengths (red). Near the horizon, the path length through the atmosphere is maximum, leading to complete scattering of the blue end of the spectrum, leaving only the red end to reach the observer. Overhead, the path length is minimal, resulting in negligible scattering, which keeps the light white.

Common Mistakes

  1. 1Confusing atmospheric refraction with scattering of light as the primary cause of the colour change.
  2. 2Stating that red light is scattered the most, whereas red light is actually scattered the least.

Interesting Facts

If the Earth had no atmosphere, the sky would look completely dark, and the Sun would appear white even during sunrise and sunset!

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2013?

This question carries 3 marks in the CBSE Class 10 Science 2013 examination.

Which chapter does this question come from in Science?

This question is from the chapter "The Human Eye and the Colourful World" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Scattering of Light" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2013 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2013 paper.