Loading PDF...
Chapter Analysis
Intermediate10 pages • EnglishQuick Summary
The chapter 'The Human Eye and the Colourful World' explains the structure and functioning of the human eye and various phenomena related to light. It covers the concepts of refraction and accommodation in the human eye, defects such as myopia, hypermetropia, and presbyopia, and their corrections. Additionally, it discusses optical phenomena such as dispersion and scattering of light, explaining occurrences like rainbows, blue sky, and twinkling of stars.
Key Topics
- •Structure of the human eye
- •Refraction and accommodation
- •Common defects of vision
- •Dispersion of light
- •Scattering of light
- •Twinkling of stars and planets
- •Formation of rainbows
- •Atmospheric refraction effects
Learning Objectives
- ✓Understand the human eye's structure and function
- ✓Explain how light is refracted through the eye
- ✓Identify and correct common vision defects
- ✓Describe dispersion and its effects
- ✓Reflect on the role of scattering in natural phenomena
- ✓Discuss the causes of twinkling and colour phenomena in the sky
Questions in Chapter
The human eye can focus on objects at different distances by adjusting the focal length of the eye lens. This is due to (a) presbyopia (b) accommodation (c) near-sightedness (d) far-sightedness.
Page 170
The human eye forms the image of an object at its (a) cornea (b) iris (c) pupil (d) retina.
Page 170
The least distance of distinct vision for a young adult with normal vision is about (a) 25 m (b) 2.5 cm (c) 25 cm (d) 2.5 m.
Page 170
The change in focal length of an eye lens is caused by the action of the (a) pupil (b) retina (c) ciliary muscles (d) iris.
Page 170
A person needs a lens of power –5.5 dioptres for correcting his distant vision. For correcting his near vision, he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?
Page 170
The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?
Page 170
Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 25 cm.
Page 170
Why is a normal eye not able to see clearly the objects placed closer than 25 cm?
Page 170
What happens to the image distance in the eye when we increase the distance of an object from the eye?
Page 170
Why do stars twinkle?
Page 170
Explain why the planets do not twinkle.
Page 170
Why does the sky appear dark instead of blue to an astronaut?
Page 170
Additional Practice Questions
Explain the reason behind the blue colour of the sky.
mediumAnswer: The blue colour of the sky is due to Rayleigh scattering. Molecules in air scatter shorter wavelengths of light, like blue, more than longer wavelengths such as red. This causes the sky to appear blue.
What happens during the dispersion of white light?
mediumAnswer: During dispersion of white light, it is split into its component colours (VIBGYOR) due to different degrees of bending experienced by each wavelength when passing through a prism.
Describe how myopia can be corrected.
easyAnswer: Myopia can be corrected using concave lenses. These lenses diverge light rays before they enter the eye, thereby moving the image back onto the retina from a point in front of it.
How can we explain the phenomenon of a rainbow?
hardAnswer: A rainbow is formed due to the refraction, dispersion, and internal reflection of sunlight by raindrops, which act as prisms. Each drop concentrates light into a spectrum of colours that is visible to the observer.
Why do we experience advance sunrise and delayed sunset?
mediumAnswer: Advance sunrise and delayed sunset occur because of atmospheric refraction. The Earth's atmosphere bends the light from the Sun, making it appear above the horizon when it is actually below it.
NCERT Exemplar
AvailablePractice with NCERT Exemplar problems and solutions for this chapter. Exemplar problems are designed to help you master the concepts with advanced-level questions.
View Exemplar