NCERT Class 10 Science Chapter 10 – The Human Eye and the Colourful World

NCERT Class 10 Science Chapter 10 explains how the human eye enables vision and how light behaves in the atmosphere. In NCERT Class 10 Science Chapter 10, students study the structure of the eye, defects of vision, dispersion of light, atmospheric refraction and scattering phenomena. NCERT Class 10 Science Chapter 10 is a high-scoring physics chapter in CBSE board exams.

NCERT Class 10 Science Chapter 10 begins with the structure of the Human Eye. Light enters through the Cornea, passes through the Pupil, and is focused by the Eye Lens onto the Retina. The image formed on the retina is Real, Inverted and Diminished. The retina contains Rods and Cones, which help in vision and colour detection.

NCERT Class 10 Science Chapter 10 explains the Power of Accommodation, which is the ability of the eye lens to change its focal length to focus objects at different distances. The Near Point of a normal eye is about 25 cm, and the Far Point is at infinity.

A major part of NCERT Class 10 Science Chapter 10 discusses Defects of Vision:

• Myopia (Short-sightedness) – Corrected using a Concave Lens
• Hypermetropia (Long-sightedness) – Corrected using a Convex Lens
• Presbyopia – Age-related defect corrected using Bifocal Lenses

NCERT Class 10 Science Chapter 10 also covers Refraction through a Prism and Dispersion of White Light. White light splits into VIBGYOR due to different wavelengths. Violet deviates the most and Red deviates the least.

Another important topic in NCERT Class 10 Science Chapter 10 is Atmospheric Refraction, which causes:

• Twinkling of stars
• Advanced sunrise and delayed sunset

Finally, NCERT Class 10 Science Chapter 10 explains Scattering of Light. Blue light scatters more than red light, which explains why the sky appears blue and the sun appears reddish at sunrise and sunset.

NCERT Class 10 Science Chapter 10 is extremely important for CBSE exams because conceptual and application-based questions are frequently asked from this chapter.

Students should refer to the official NCERT website at for authentic textbooks and syllabus updates.

For structured preparation of NCERT Class 9–12 for UPSC, BPSC and State PCS examinations, strengthen your basics with our complete NCERT Book Notes PDF for Class 9-12, available inside the NCERT foundation course level-2.

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10.1 The human eye

• The Human Eye is a natural optical instrument that enables us to see objects by forming images on the Retina.
• Light enters the eye through the transparent outer covering called the Cornea, where most refraction of light occurs.
• The amount of light entering the eye is controlled by the Iris, and the opening in the iris is called the Pupil.
• The Eye Lens is a transparent, flexible, convex lens that further refracts light to focus it on the retina.
• The Retina contains light-sensitive cells called Rods and Cones; rods help in dim light vision, while cones help in colour vision.
• The point where the optic nerve leaves the eye is called the Blind Spot, which has no photoreceptor cells.
• The image formed on the retina is Real, Inverted and Diminished.
• The Optic Nerve carries visual signals from the retina to the brain for interpretation.

10.1.1 Power of Accommodation

• The Power of Accommodation is the ability of the eye lens to change its focal length to focus objects at different distances.
• When we look at a Distant Object, the ciliary muscles relax, making the eye lens thinner and increasing its focal length.
• When we look at a Nearby Object, the ciliary muscles contract, making the eye lens thicker and decreasing its focal length.
• This adjustment ensures that images of objects at various distances are formed clearly on the Retina.
• The Near Point of a normal human eye is about 25 cm, which is the minimum distance for distinct vision.
• The Far Point of a normal eye is at Infinity, meaning distant objects can be seen clearly.
• The ability of accommodation decreases with age, leading to difficulty in focusing nearby objects.

10.2 Defects of vision and their correction

• A Defect of Vision occurs when the eye cannot focus light properly on the Retina, leading to blurred images.
• Myopia (Short-sightedness) is a defect in which nearby objects are seen clearly but distant objects appear blurred.
• Myopia occurs when the image is formed in front of the Retina, and it is corrected using a Concave Lens.
• Hypermetropia (Long-sightedness) is a defect in which distant objects are seen clearly but nearby objects appear blurred.
• Hypermetropia occurs when the image is formed behind the Retina, and it is corrected using a Convex Lens.
• Presbyopia is an age-related defect caused by weakening of ciliary muscles and reduced power of accommodation.
• Presbyopia can be corrected using Bifocal Lenses, which have both concave and convex portions.
• Proper use of corrective lenses restores the image formation on the retina and ensures clear vision.

10.3 Refraction of light through a prism

• A Prism is a transparent refracting medium bounded by two plane surfaces inclined at a certain angle called the Angle of Prism (A).
• When a ray of light passes through a prism, it undergoes Refraction at both the surfaces.
• The angle between the incident ray and the emergent ray is called the Angle of Deviation (δ).
• The deviation depends on the Angle of Incidence, the Angle of Prism and the Refractive Index of the material.
• For a given prism and a particular wavelength, there is a specific angle of incidence at which the angle of deviation is Minimum (δm).
• At the position of minimum deviation, the path of light inside the prism becomes symmetrical.
• Refraction through a prism results in bending of light towards the base of the prism.

10.4 Dispersion of white light by a glass prism

• Dispersion is the phenomenon of splitting of White Light into its constituent colours when it passes through a Glass Prism.
• White light consists of seven colours forming the spectrum called VIBGYOR – Violet, Indigo, Blue, Green, Yellow, Orange and Red.
• Different colours bend by different amounts because they have different Wavelengths and Refractive Indices in glass.
• Violet Light deviates the most, while Red Light deviates the least.
• The band of coloured light obtained on a screen is called the Spectrum.
• When the dispersed colours are passed through another identical prism placed in inverted position, they recombine to form White Light again.
• Dispersion explains natural phenomena such as formation of a Rainbow.

10.5 Atmospheric refraction

• Atmospheric Refraction occurs due to gradual change in density of air layers in the atmosphere.
• Light from distant objects such as stars bends continuously while passing through layers of air of varying density.
• Due to atmospheric refraction, stars appear to Twinkle because their light undergoes random refraction.
• Planets do not twinkle significantly because they appear as extended sources of light.
• Atmospheric refraction also causes the Advanced Sunrise and Delayed Sunset, making the Sun visible about 2 minutes earlier and 2 minutes later than its actual position.
• During sunrise and sunset, the Sun appears Flattened due to refraction of light through different atmospheric layers.
• The apparent position of celestial objects differs from their actual position because of atmospheric refraction.

10.6 Scattering of light

• Scattering of Light is the phenomenon in which light is redirected in different directions when it strikes small particles in a medium.
• The amount of scattering depends on the Wavelength of Light and the size of particles present.
• Shorter wavelengths scatter more than longer wavelengths.
• Blue Light is scattered more strongly than red light because it has a shorter wavelength.
• Scattering is responsible for various natural phenomena observed in the sky.
• When sunlight passes through the atmosphere, dust and air molecules scatter light in different directions.
• This scattering effect explains the colour changes observed during sunrise and sunset.

10.6.1 Tyndall Effect

• The Tyndall Effect is the scattering of light by colloidal particles present in a medium.
• When a beam of light passes through a colloid, the path of the beam becomes visible due to scattering.
• This effect occurs because colloidal particles are large enough to scatter light.
• The Tyndall effect can be observed when sunlight enters a dusty room through a small opening.
• It is also seen in fog, mist or smoke where tiny particles scatter light.
• The colour of the scattered light depends on the Size of Particles and the Wavelength of Light.
• The Tyndall effect demonstrates the phenomenon of scattering in everyday life.

10.6.2 Why is the Colour of the Clear Sky Blue?

• The colour of the clear sky appears Blue due to the scattering of sunlight by molecules of air in the atmosphere.
• Sunlight consists of different colours with different Wavelengths.
• Blue Light has a shorter wavelength and is scattered more strongly than red light.
• When sunlight enters the atmosphere, blue light is scattered in all directions by air molecules.
• As a result, when we look at the sky, scattered blue light reaches our eyes from every direction.
• During Sunrise and Sunset, the Sun appears reddish because most of the blue light is scattered away before reaching our eyes.
• The phenomenon responsible for the blue colour of the sky is called Rayleigh Scattering.

Exam Oriented Facts

• The image formed on the Retina is Real, Inverted and Diminished.
• Cornea causes most of the refraction of light entering the eye.
• Iris controls the size of the Pupil, thereby regulating the amount of light entering the eye.
• Eye Lens is a flexible convex lens that changes shape for focusing.
• Rods help in dim light vision; Cones help in colour vision.
• The point where optic nerve leaves the retina is the Blind Spot.
• Near Point of a normal eye = 25 cm.
• Far Point of a normal eye = Infinity.
• Ability of eye lens to change focal length is called Power of Accommodation.
• Decreases with age, leading to Presbyopia.
• Myopia (Short-sightedness) → Image forms in front of retina → Corrected by Concave Lens.
• Hypermetropia (Long-sightedness) → Image forms behind retina → Corrected by Convex Lens.
• Presbyopia → Age-related defect → Corrected by Bifocal Lenses.
• Angle of Prism (A) is the angle between the two refracting surfaces.
• Angle of Deviation (δ) is the angle between incident and emergent rays.
• White light splits into VIBGYOR spectrum.
• Violet deviates the most; Red deviates the least.
• Recombination of colours produces white light again.
• Causes Twinkling of Stars.
• Causes Advanced Sunrise and Delayed Sunset (~2 minutes).
• Sun appears flattened at horizon due to atmospheric refraction.
• Shorter wavelength → More scattering.
• Blue light scatters more than red light.
• Tyndall Effect is scattering by colloidal particles.
• Clear sky appears Blue due to scattering of blue light.
• Sun appears Red at Sunrise and Sunset because blue light is scattered away.

NCERT Class 10 Science Chapter 10 – The Human Eye and the Colourful World strengthens understanding of vision, light behaviour and atmospheric phenomena. A strong grasp of NCERT Class 10 Science Chapter 10 ensures clarity in ray diagrams and real-life applications.

NCERT Class 10 Science Chapter 10 is a scoring chapter for CBSE board exams and forms the base for advanced optics in higher classes.

Continue reading NCERT Class 10 Science Chapter 11 – Electricity to explore electric current and circuits.

FAQs

Q1. What is NCERT Class 10 Science Chapter 10 about?
NCERT Class 10 Science Chapter 10 explains the human eye, defects of vision, dispersion, atmospheric refraction and scattering.

Q2. What is the near point of a normal eye in NCERT Class 10 Science Chapter 10?
25 cm.

Q3. Which defect is corrected by a concave lens in NCERT Class 10 Science Chapter 10?
Myopia.

Q4. Why does the sky appear blue according to NCERT Class 10 Science Chapter 10?
Because blue light scatters more in the atmosphere.

Q5. Why is NCERT Class 10 Science Chapter 10 important for exams?
Because it includes conceptual and application-based questions frequently asked in CBSE exams.

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