Class 10 Science Chapter 11 The Human Eye and the Colourful World
Though, all parts of our body are of equal importance, but, eyes are very special. It is because of these eyes that we are able to see this colourful world and its beauty. So, here in this article, we will study class 10 science chapter 11 the human eye and the colorful world. We will connect the knowledge that we gained from the previous chapter i.e light – reflection and refraction and see how this knowledge helps in correcting vision and much more.
In this chapter, we will learn different things like, how images are formed in our eyes, different types of defects in a vision and how it can be corrected, different types of phenomena occurring in nature due to light’s reflection and reflection, etc.
Class 10 Science Chapter 11 The Human Eye and the Colourful World
Have you ever thought about why are our eyes situated in front of our heads, and why not at the sides like other animals? well, if you have read NCERT, then you will know the answer, and if not, then look into it, you will find your answer there. Now, let’s discuss the main topics of this chapter.
The format for class 10 science chapter 11 the human eye and the colourful world is going to be simple, we will cover the important definitions and points related to a topic to give a quick view of a topic.
# 11.1 — The Human Eye
The important parts of the human eye, their roles, and how an image is formed on the eye are given in this section. Let’s take a look at the roles of different parts of an eye.
Retina: It is a delicate membrane that has a huge amount of light-sensitive cells. The image of an object is formed on the retina of the eye. The light-sensitive cells generate and send electrical signals to the brain via optic nerves.
Cornea: It is a thin membrane through which light enters the eye. It covers the eyeball by forming a transparent bulge on the front surface of the eyeball. Most of the refraction of light that enters the eye occurs at the outer surface of the cornea.
Eyeball: The front part of the eye that we can see from the outside is called the eyeball. its shape is almost spherical and has around 2.3 cm in diameter.
Iris: it is a dark muscular diaphragm that controls the size of the pupil.
Pupil: the role of the pupil is to control the amount of light that enters the eye. It expands when there is less light (to absorb more light) and shrinks when there is extra light (to restrict more light from entering the eye).
11.1.1 — Power of accommodation
This is the sub-topic of the human eye in class 10 science chapter 11 the human eye and the colourful world.
The ability of a human eye lens to adjust its focal length to see distant or nearby objects is called the power of accommodation. The human eye lens is made up of jelly-like material and its curvature can adjust to some extent.
When we look at distant objects then the eye muscles are relaxed and the eye lens becomes thin, due to which its focal length increases and we are able to see distant objects clearly. In the same manner, when we look at nearby objects, the eye lens becomes thicker decreases its focal length and enables us to see nearby objects clearly.
Class 10 Science Chapter 11 The Human Eye and the Colourful World
So far we have learned about the different parts of the human eye and how it adjusts itself the see near and distant objects. Now, we will learn about the vision defects of the eye and how they can be corrected.
# 11.2 — Defects of vision and their correction
When the eye loses the power of accommodation, then there arise vision defects. In this section of class 10 science chapter 11 the human eye and the colourful world, we will learn about these defects. There are mainly the following there common refractive defects:
(a) — Myopia or nearsightedness: In myopia, nearby objects can be seen clearly, but not distant objects. Myopia happens when the image of a distant object is formed in front of the retina instead of forming at the retina itself. This can happen due to excessive curvature of the eye lens, or due to the elongation of the eyeball.
This defect is corrected by using a concave lens of suitable power which brings the image back on the retina.
(b) — Hypermetropia or farsightedness: hypermetropia is exactly the opposite of myopia. In this, distant objects can be seen clearly, but not near ones. In this, the image of the object is formed behind the retina. This may happen when the focal length of the eye else gets too long, or when the eyeball has become too small.
We overcome this defect by using a convex lens of appropriate power that provides additional focusing power.
(c) — Presbyopia: When a defect in vision is caused due to ageing i.e the power of accommodation gradually decreases due to ageing, then it is known as presbyopia. Usually, people with presbyopia suffer from nearsightedness.
Note: People suffering from both presbyopia and hypermetropia need bi-focal lenses that have a concave lens on the upper part and a convex lens on the lower part.
# 11.3 — Refraction of light through a prism
In the earlier chapter, we learned how light rays get refracted through a glass slab that is rectangular in shape. In class 10 science chapter 11 the human eye and the colourful world, we will see the behaviour of light when it travels through a prism.
What is a prism?
It is a triangle-shaped glass that has two triangular bases and three rectangular lateral surfaces. The angle between its two lateral faces is called the angle of the prism.
Class 10 Science Chapter 11 The Human Eye and the Colourful World
Since we know what prims is, therefore, we are now in the right position to learn the other behaviours of light when it passes through the prism. So, let’s get going!
# 11.4 — Dispersion of white light by a glass prism
Dispersion: The splitting of light into its component colours is called dispersion.
Spectrum: The band of the coloured component of a light beam is called its spectrum.
When white light passes through a prism then it scatters into seven different coloured components. The seven colours are Violet, Indigo, Blue, Green, Yellow, Orange, Red. The sequence can be remembered as VIBGYOR. This pattern can also be seen in the rainbow which is formed when light rays pass through tiny droplets that act as prisms. Isaac Newton discovered the dispersion of white light.
# 11.5 — Atmospheric refraction
In this section of class 10 science chapter 11 the human eye and the colourful world, we will learn about different phenomena that happen in nature due to the refraction of light.
Twinkling of stars: Right after entering the earth’s atmosphere, the path of rays of light coming from the star goes on varying slightly, the apparent position of the star also fluctuates, and the amount of starlight entering the eye flickers and this is why the star sometimes appear brighter and sometimes fainter, giving a twinkling effect.
Advance sunrise and delayed sunset: We see the sunrise approx 2 minutes before it actually rises. We also see the sunset about 2 minutes before the actual sunset. This is due to atmospheric refraction.
Class 10 Science Chapter 11 The Human Eye and the Colourful World
Why is the colour of the sky is blue? why do we see different colours at sunrise and sunset? these are some questions that will be answered in this section of class 10 science chapter 11 the human eye and the colourful world.
# 11.6 — Scattering of light
11.6.1 — Tyndall Effect
The phenomenon of scattering of light by the colloidal particles gives rise to the Tyndall effect.
11.6.1 — Why is the colour of the clear sky blue?
The size of fine particles present in the atmosphere is smaller than the wavelength of visible light, therefore, these particles scatter light of shorter wavelengths. Since we know that blue has a shorter wavelength, therefore, it is scattered the most in the atmosphere, and hence we see the clear sky blue.
11.6.1 — Colour of the sun at sunrise and sunset
Light rays coming from the sun near the horizon passes through thicker layers of air and travels a greater distance in the earth’s atmosphere, this is why we see the reddish colour on sunrise and sunset. But, during noon when the sun is overhead, the light coming from it has to travel a shorter distance, and this is why the sun appears white at noon.