CBSE Class 10/Overview
Curriculum 2026–27
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ScienceCh-10 15 min comprehensive revision
NCERT Class 10 Science — Chapter 11

The Human Eye and the Colourful World

Human eye anatomy, power of accommodation, vision defects (Myopia, Hypermetropia, Presbyopia) and their lens corrections, prism dispersion (VIBGYOR), atmospheric refraction (twinkling of stars, advanced sunrise), and scattering of light (Tyndall effect, blue sky, reddish sun).

Quick Key Takeaways:
Power of Accommodation: The ability of the eye lens to adjust its focal length using ciliary muscles. Near point of distinct vision for normal eye =25 cm= 25\text{ cm}; Far point =∞= \infty (infinity).
Vision Defects & Corrections:
- Myopia (Near-sightedness): Far point comes closer than infinity; image forms in front of retina; corrected using Concave lens (P<0P < 0).
- Hypermetropia (Far-sightedness): Near point recedes farther than 25 cm; image forms behind retina; corrected using Convex lens (P>0P > 0).
- Presbyopia: Loss of accommodation due to aging; corrected using Bifocal lenses (upper concave for distant, lower convex for reading).
Prism Dispersion: White light splits into 7 constituent spectrum colours (VIBGYOR - Red bends least due to longest wavelength; Violet bends most due to shortest wavelength). Recombination achieved using an inverted identical second prism (Newton's experiment).
Atmospheric Phenomena: (1) Twinkling of stars (continuous fluctuations in atmospheric density/refractive index); (2) Advanced sunrise & delayed sunset (by 2 minutes each due to atmospheric refraction); (3) Blue sky & Red sunset (Rayleigh scattering ∝1/λ4\propto 1/\lambda^4; blue scatters most, red scatters least).
Jump to Concept:1. 1. Eye Anatomy, Accommodation & Vision Defect Corrections2. 2. Prism Dispersion, Atmospheric Refraction & Light Scattering3. 3. High-Yield Solved Board Examination Questions (3-Mark & 5-Mark)4. 4. Practical Laboratory & Competency-Based Case Drill: Newton's Prism Spectrum Recombination Experiment5. 5. CBSE Examiner Marking Scheme, Scientific Notation & Deduction Traps
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1. Eye Anatomy, Accommodation & Vision Defect Corrections

Fundamental Principles

Core scientific laws, chemical equations, anatomical structures, and visual model for The Human Eye and the Colourful World.

• Human Eye Anatomy & Working of Ciliary Muscles
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Cornea: Thin, transparent front membrane that performs ~80% of light refraction.
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Iris & Pupil: Iris controls pupil size to regulate light entry (constricts in bright light, dilates in dim light).
•
Ciliary Muscles Action:
- Viewing distant objects: Ciliary muscles relax, lens becomes thin, focal length increases.
- Viewing nearby objects: Ciliary muscles contract, lens becomes thick/rounded, focal length decreases.
•
Retina: Light-sensitive screen containing photoreceptor cells (Rods for light intensity, Cones for colour vision) that send electrical impulses via Optic Nerve to brain.
📊 Human Eye & Spectrum: Vision Defects & Prism DispersionVisual Model
1. MYOPIA (Near-Sightedness)Image In FrontCorrection: CONCAVE Lens (Diverging)2. HYPERMETROPIA (Far-Sighted)Image BehindCorrection: CONVEX Lens (Converging)

Visual schematic mapping human eye ciliary accommodation, myopia/hypermetropia ray corrections, prism dispersion, and atmospheric refraction.

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2. Prism Dispersion, Atmospheric Refraction & Light Scattering

Mechanisms & Experiments

Step-by-step chemical reaction mechanisms, experimental activities, and physiological pathways for The Human Eye and the Colourful World.

• Atmospheric Refraction & Rayleigh Scattering
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Dispersion of White Light: Different wavelengths travel at different speeds in glass. Red has the longest wavelength (λ\lambda) and highest speed in glass, so it deviates the least; Violet has the shortest λ\lambda and lowest speed, so it deviates the most.
•
Why Stars Twinkle but Planets Do Not:
- Stars are point-sized distant sources; their light path continually bends through fluctuating atmospheric layers, causing apparent brightness to flicker.
- Planets are closer extended sources (cluster of point sources); fluctuations from different points average out, nullifying the twinkling effect.
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Why Sky is Blue & Sun is Red at Sunrise/Sunset:
- Fine air molecules (N2,O2N_2, O_2) have sizes smaller than visible light wavelength, scattering blue light much more strongly than red (I∝1/λ4I \propto 1/\lambda^4).
- At sunrise/sunset, sunlight passes through a much greater thickness of atmosphere; most blue light is scattered away, leaving only longer red wavelengths to reach our eyes.
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3. High-Yield Solved Board Examination Questions (3-Mark & 5-Mark)

Solved Board Questions

Standard CBSE board exam questions with complete scientific justifications and marking scheme step protocols.

• 3-Mark Standard Board Question: A student unable to see clearly the blackboard from the last row is advised to wear spectacles.
(a) Name the defect of vision the student is suffering from.
(b) List two possible causes of this defect.
(c) Name the type of lens used for correction and explain with ray diagrams.
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(a) Name of Defect: Myopia (Near-sightedness / Short-sightedness).
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(b) Two Root Causes:
1. Excessive curvature of the eye lens (lens is too thick/converging).
2. Elongation of the eyeball (distance between lens and retina is too large).
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(c) Lens Correction & Working:
- Corrected using a Concave Lens of suitable focal length/power.
- The concave lens diverges incoming parallel light rays from the distant blackboard before they enter the eye, making them appear as if they originate from the student's near-myopic far point, forming a sharp image directly on the retina.
• 5-Mark Comprehensive Question / Numerical: The near point of a hypermetropic eye is 1 m. Find the power of the lens required to read a book held at 25 cm. (Assume eye lens distance is negligible).
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Step 1 (Given Data):
- Object distance u=−25 cm=−0.25 mu = -25\text{ cm} = -0.25\text{ m} (normal near point).
- Defective near point (image distance) v=−1 m=−100 cmv = -1\text{ m} = -100\text{ cm}.
- Focal length f=?f = ?, Power P=?P = ?.
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Step 2 (Applying Lens Formula):
1v−1u=1f\frac{1}{v} - \frac{1}{u} = \frac{1}{f}
1−100−(1−25)=1f  ⟹  −1100+125=1f\frac{1}{-100} - \left(\frac{1}{-25}\right) = \frac{1}{f} \implies -\frac{1}{100} + \frac{1}{25} = \frac{1}{f}
−1+4100=1f  ⟹  3100=1f\frac{-1 + 4}{100} = \frac{1}{f} \implies \frac{3}{100} = \frac{1}{f}
f=+1003 cm=+13 meter\mathbf{f = +\frac{100}{3}\text{ cm} = +\frac{1}{3}\text{ meter}}
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Step 3 (Calculating Power):
P=1f (in meters)=1+1/3=+3.0 Dioptres (D)P = \frac{1}{f\text{ (in meters)}} = \frac{1}{+1/3} = \mathbf{+3.0\text{ Dioptres (D)}}
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Conclusion: The person requires a Convex Lens of power +3.0 D+3.0\text{ D} to correct hypermetropia.
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4. Practical Laboratory & Competency-Based Case Drill: Newton's Prism Spectrum Recombination Experiment

Practical & Case Drill

Experimental observation analysis, chemical gas tests, and assertion-reason drills.

• Laboratory Activity Context: Newton's Prism Spectrum Recombination Experiment
Sir Isaac Newton passed a beam of white sunlight through a glass prism to produce a VIBGYOR spectrum, and then placed an identical inverted second prism in the path of the spectrum.
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Q1: What emerged from the second inverted prism? →\rightarrow A single beam of pure white light emerged.
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Q2: What important scientific conclusion did Newton draw? →\rightarrow Sunlight / White light is not a single colour, but is fundamentally composed of seven constituent spectrum colours.
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Q3: Name the natural atmospheric phenomenon that acts as a spectrum prism. →\rightarrow Formation of a Rainbow (where suspended spherical raindrops act as tiny prisms undergoing refraction, dispersion, and internal reflection).
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5. CBSE Examiner Marking Scheme, Scientific Notation & Deduction Traps

Important Solved Board Questions

Examiner step-marking allocations, mandatory scientific terminology, and common error avoidance.

• Step-by-Step Marking Rubric & Key Terminology
•
1 Mark: Stating near point (25 cm) and far point (∞\infty) for a normal eye.
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2 Marks: Numerical solution of lens formula for myopia/hypermetropia correction.
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1 Mark: Correct explanation of Rayleigh scattering and blue sky.
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1 Mark: Accurate ray diagram of prism dispersion (VIBGYOR ordering).
• Common Error Deduction Traps
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Trap 1: Reversing VIBGYOR order (Violet bends most at the bottom; Red bends least at the top).
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Trap 2: Confusing concave lens (for myopia) with convex lens (for hypermetropia).
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Trap 3: Writing that planets do not twinkle because they have no light (they do not twinkle because they are large extended sources).
Authentic Board Question (3 Marks)Topic: The Human Eye and the Colourful World Laws of Physics & Numerical Problem Solving
State the governing physical law, write the standard formula with Cartesian sign conventions, and solve the numerical/diagram application for The Human Eye and the Colourful World.

Official CBSE Step-by-Step Marking Breakdown:

Step 1: Law / Formula & Sign Convention Setup: State the formal governing physical law (Ohm's Law, Joule's Heating, Mirror/Lens formula) with Cartesian sign conventions (u,v,fu, v, f).
1 Mark
Step 2: Step-by-Step Algebraic Substitution & Calculation: Substitute given values systematically showing all intermediate algebraic simplification steps.
1 Mark
Step 3: Boxed Final Answer with Proper SI Units & Direction: State the final numerical result clearly boxed with mandatory SI units (Ω,V,A,W,J,cm,D\Omega, \text{V}, \text{A}, \text{W}, \text{J}, \text{cm}, \text{D}) and ray/field directional arrows.
1 Mark
Model Student Answer (Target: Full 3/3 Marks):
To score full 3 marks on The Human Eye and the Colourful World in CBSE Science (Physics):

1. Formula & Conventions: Write the governing formula (e.g., V=IRV = IR, 1f=1v−1u\frac{1}{f} = \frac{1}{v} - \frac{1}{u}) and assign correct signs to given quantities.
2. Calculation Steps: Substitute values clearly and show each arithmetic reduction line.
3. Final Result: Box the final numerical value with mandatory SI units (e.g. R=10 ΩR = 10\,\Omega, P=100 WP = 100\,\text{W}, f=−15 cmf = -15\,\text{cm}).
Examiner Mark Deduction Traps:
•Always assign Cartesian sign conventions before substituting into mirror/lens formulas.
•Never write a pure number without its mandatory SI unit—examiners deduct ½ mark for missing units.

High-Frequency Conceptual Doubts & FAQs

Curated answers to the most common questions asked by Class 10 students.
This chapter establishes the foundational principles, definitions, and operational workflows required for Class 10 board mastery.

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