CBSE Class 10 Science • Vision and Optical Phenomena
The Human Eye and the Colourful World Class 10 Worksheet
How does your eye focus on a nearby book and a distant tree? Why do stars twinkle, and why does the clear sky appear blue? Use The Human Eye and the Colourful World Class 10 worksheet to practise the eye’s structure, accommodation, defects of vision, dispersion, atmospheric refraction and scattering of light.
This chapter connects the mirror and lens concepts you have already studied with vision and familiar natural phenomena. Understanding where light focuses and how it travels through the atmosphere helps you explain observations using the correct scientific principle.
Before attempting the worksheet, review our Human Eye and the Colourful World notes and mind map . Then practise the questions independently. The short notes, worked examples and answers below provide additional support for revision.
Human Eye Class 10 Summary: Parts and Functions
Light enters the eye through the cornea and pupil. The cornea provides most of the eye’s refraction, while the eye lens adjusts the focus. A real, inverted image forms on the retina, where light-sensitive cells produce signals that travel to the brain.
| Part | Main function |
|---|---|
| Cornea | Transparent front surface that provides most of the refraction. |
| Iris | Controls pupil size and regulates the amount of light entering. |
| Pupil | Opening through which light enters the eye. |
| Eye lens | Adjusts focus so that images form on the retina. |
| Ciliary muscles | Help change lens curvature during accommodation. |
| Retina | Contains photoreceptors that detect light. |
| Optic nerve | Carries visual information from the retina towards the brain. |
Power of Accommodation Class 10
Accommodation is the eye’s ability to adjust its lens power to focus on objects at different distances. For a distant object, the ciliary muscles relax and the lens becomes less curved. For a nearby object, the ciliary muscles contract and the lens becomes more curved, increasing its power.
Near Point and Far Point
In the standard model of a normal young eye, the near point is about 25 cm and the far point is at infinity. The near point is the closest distance for clear vision without excessive strain. It varies with age and between individuals.
Defects of Vision and Their Correction
| Defect | Difficulty | Optical explanation | Correction |
|---|---|---|---|
| Myopia | Distant objects appear blurred. | Light from a distant object focuses in front of the retina. | A concave lens of suitable power. |
| Hypermetropia | Nearby objects are difficult to see clearly. | For a nearby object, the focus would lie behind the retina. | A convex lens of suitable power. |
| Presbyopia | Near vision becomes more difficult with age. | Age-related reduction in accommodation, particularly as the lens becomes less flexible. | Suitable near-vision lenses; bifocal or progressive lenses when needed. |
Myopia: Why a Concave Lens Helps
Myopia can result from excessive converging power or an elongated eyeball. A concave lens diverges incoming light so the eye can focus it on the retina. For a distant object, the correcting lens produces a virtual image at the eye’s far point.
Hypermetropia: Why a Convex Lens Helps
Hypermetropia can result from insufficient converging power or a shorter eyeball. A convex lens adds convergence, helping the eye focus light from nearby objects on the retina.
Do Not Confuse Presbyopia with Myopia
Presbyopia concerns reduced accommodation with age. A person may also have myopia or hypermetropia, so the required correction depends on both distance and near-vision needs.
Human Eye Class 10 Numericals with Solutions
Example 1: Correcting Myopia
A myopic eye has a far point of 2 m. Find the approximate power of the correcting lens, assuming it is close to the eye.
Object distance = infinity
Required virtual image distance = −2 m
1/f = 1/v − 1/u
1/f = −1/2 − 0
f = −2 m
P = 1/f
P = −0.5 D
Answer: A concave lens of power −0.5 D.
Example 2: Correcting Hypermetropia
A person’s near point is 50 cm. Find the approximate lens power needed to view an object at 25 cm, assuming the lens is close to the eye.
u = −25 cm
v = −50 cm
1/f = 1/v − 1/u
1/f = −1/50 + 1/25
1/f = 1/50
f = +50 cm
f = +0.50 m
P = 1/f
P = +2 D
Answer: A convex lens of power +2 D. It produces a virtual image at the person’s near point.
Dispersion of White Light Through a Prism
Dispersion is the separation of white light into its constituent colours. Ordinary glass has different refractive indices for different wavelengths, so the colours deviate by different amounts. Violet deviates more than red in the usual glass-prism experiment.
Remember the Spectrum
Violet, indigo, blue, green, yellow, orange and red are commonly remembered as VIBGYOR. The visible spectrum is continuous; these names describe regions within it.
A suitably arranged second prism can recombine the separated colours to produce white light.
How Does a Rainbow Form?
A primary rainbow forms when sunlight enters water droplets, undergoes refraction and dispersion, reflects internally and refracts again on leaving. The Sun is behind the observer and the droplets are ahead. Red appears on the outer edge and violet on the inner edge of the primary rainbow.
Atmospheric Refraction Class 10
Atmospheric refraction is the bending of light as it travels through air layers with varying refractive index. It helps explain apparent shifts in celestial positions and changes in the light received from distant sources.
Why Do Stars Twinkle?
Stars appear nearly point-like because of their great distance. Changing atmospheric conditions cause fluctuations in their apparent position and received brightness, producing twinkling. Planets usually twinkle much less because their apparent discs allow many small fluctuations to average out.
Advance Sunrise and Delayed Sunset
Atmospheric refraction allows the Sun to appear above the horizon when it is geometrically just below it. In the standard textbook explanation, sunrise appears about two minutes early and sunset about two minutes late.
Scattering of Light and the Blue Sky
Scattering redirects light in different directions. Air molecules scatter shorter visible wavelengths more strongly than longer ones. Scattered sunlight reaching our eyes makes the clear daytime sky appear blue.
Tyndall Effect
The Tyndall effect makes a light beam visible when it passes through a colloid or a suitable fine suspension. Particles scatter light towards the observer. A beam passing through mist or a colloidal mixture provides a familiar example.
Match the Observation to the Correct Principle
Prism spectrum: dispersion.
Twinkling stars: changing atmospheric refraction.
Blue sky: scattering.
Focusing near and far objects: accommodation.
Human Eye and the Colourful World Class 10 MCQs
1. Which part controls the size of the pupil?
A. Retina
B. Iris
C. Optic nerve
D. Cornea
Answer: B. Iris. It adjusts the pupil opening and regulates light entry.
2. Which lens corrects myopia?
A. Convex lens
B. Concave lens
C. Plane glass only
D. No optical lens
Answer: B. Concave lens. It diverges light before it enters the eye.
3. Which colour deviates least through an ordinary glass prism?
A. Violet
B. Blue
C. Green
D. Red
Answer: D. Red. Red light deviates less than violet light in this experiment.
Assertion–Reason Practice
Assertion: A concave lens can correct myopia.
Reason: It diverges incoming rays, helping the eye focus them on the retina instead of in front of it.
Answer: Both statements are true, and the reason correctly explains the assertion.
Case-Based Questions with Answers
Case Study: Reading the Classroom Board
A student can read a nearby book clearly but finds writing on a distant classroom board blurred. An eye examination identifies myopia.
Question 1: Where would distant-object light focus
without correction?
In front of the retina.
Question 2: Which correcting lens is used?
A concave lens of suitable power.
Question 3: What is the sign of its power?
Negative.
Question 4: What does the lens do to incoming rays?
It diverges them so the eye can focus them on the retina.
Important Questions and Diagram Practice
- Draw the human eye and label its main parts.
- Explain accommodation when viewing near and distant objects.
- Compare myopia, hypermetropia and presbyopia.
- Draw ray diagrams showing myopia and its correction.
- Draw ray diagrams showing hypermetropia and its correction.
- Calculate correcting-lens power using signed distances.
- Explain dispersion through a glass prism.
- Describe the formation of a primary rainbow.
- Explain why stars twinkle and planets usually twinkle less.
- Explain the blue sky and the Tyndall effect.
How to Revise with This Worksheet
Attempt the worksheet independently, then review your answers. For eye-defect diagrams, mark the retina and show where rays focus before and after correction. For numericals, use the lens formula with correct signs and convert focal length to metres before calculating power.
For natural phenomena, name the principle first and explain how it produces the observation. This helps keep scattering, dispersion and atmospheric refraction separate.
Frequently Asked Questions
What is the difference between the iris and pupil?
The iris is the coloured structure that controls the opening. The pupil is the opening through which light enters.
Does the eye focus by changing the distance between the lens and retina?
In normal accommodation, the lens mainly changes curvature and power. The lens-to-retina distance stays approximately fixed.
Why does the eye need accommodation?
Light from near and distant objects reaches the eye differently. Adjusting lens power keeps the image focused on the retina.
Does everyone’s near point equal exactly 25 cm?
No. About 25 cm is a standard reference for a normal young eye. The actual near point varies with age and between individuals.
Are bifocal lenses needed for every person with presbyopia?
No. The correction depends on near and distance vision needs. Some people use reading lenses, while others require bifocal or progressive lenses.
Why is the sky blue rather than violet?
The perceived colour depends on the sunlight spectrum, atmospheric transmission and the sensitivity of human vision. Strong short-wavelength scattering does not make the sky appear purely violet.
Why does the sky appear dark from space?
Away from a substantial atmosphere, very little sunlight is scattered into the observer’s line of sight. The background therefore appears dark.
Do planets never twinkle?
Planets generally twinkle less than stars because their apparent discs average atmospheric fluctuations. Some twinkling can occur, especially near the horizon.
Does a prism create the colours in white light?
No. It separates wavelengths already present in white light because different wavelengths are refracted by different amounts.
Where can I find related notes and a mind map?
Visit our Human Eye and the Colourful World notes and mind map before returning to the worksheet for practice.
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