Q19
1 markMCQSection A

Assertion (A): Red light signals are used to stop the vehicles on the road. Reason (R): Red coloured light is scattered the most so as to be visible from a large distance.

The Human Eye and the Colourful World
Scattering of Light

Options

(A)Both (A) and (R) are true and (R) is the correct explanation of (A).
(B)Both (A) and (R) are true and (R) is not correct explanation of (A).
(C)(A) is true, but (R) is false.
(D)(A) is false, but (R) is true.
Official Answer

The correct option is C.

Red lightScattered the leastLongest wavelengthStop signals

Marking Scheme

  • 11 mark for identifying that Assertion (A) is true but Reason (R) is false (Option C).

Hint

Recall how scattering depends on wavelength. Does red light, which has a longer wavelength, scatter more or less than blue light?

Quick Oral Answer

Red light is used for stop signals because it has a longer wavelength and is scattered the least by dust and smoke particles, allowing it to be seen clearly from a distance.

Analysis & Explanation

  • Assertion (A) is true: Red light signals are universally used to stop vehicles because red light can be seen from a very large distance, even through fog or smoke.
  • Reason (R) is false: According to the principles of scattering, red light has the longest wavelength in the visible spectrum and is scattered the least (not the most) by air molecules and dust particles. Because it is scattered the least, it can travel long distances without losing its intensity, making it highly visible from afar.

Therefore, Assertion (A) is true but Reason (R) is false.

Common Mistakes

  1. 1Students often incorrectly assume that because red light is highly visible, it must be scattered the most, whereas the opposite is true: it is visible because it is scattered the least.

Interesting Facts

Since red light is scattered the least by atmosphere particles, it is the last color to be filtered out, which is also why the Sun appears reddish during sunrise and sunset.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2024?

This question carries 1 mark in the CBSE Class 10 Science 2024 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 2024 paper?

This is a MCQ question from Section A in the CBSE Class 10 Science 2024 paper.