Class 10 Science · Original EZT practice
The Human Eye and the Colourful World (Class 10 Chapter 10): summary and practice
The eye is a living lens system, and this chapter uses it to tie together refraction, lenses and colour: how the eye focuses, what goes wrong in myopia and hypermetropia, and why prisms, skies and sunsets show colour. All questions are original EZT tutor practice following the chapter's own section order.
8 original worked examples, 8 fresh self-check questions and 4 mixed questions, with explained answers. These are not copied textbook exercises, an official chapter index or a full answer key. No affiliation with NCERT is claimed.
Official sources for topic and edition context, checked 20 October 2026:
1. The human eye
The cornea and the eye lens focus light onto the retina, the iris controls the pupil, and the ciliary muscles adjust the lens. For a normal eye the near point is about 25 cm and the far point is at infinity.
2. Defects of vision and their correction
In myopia the eye focuses distant objects in front of the retina; a concave lens corrects it. In hypermetropia near objects focus behind the retina; a convex lens corrects it. Presbyopia combines both and may need bifocal lenses.
3. Prism and dispersion
A prism bends light toward its base. White light splits into the spectrum - violet bends the most and red the least - because each colour refracts by a different amount.
4. Atmospheric refraction and scattering
Refraction through layers of air makes stars twinkle and advances sunrise. Scattering by air molecules explains the Tyndall effect and why the clear sky is blue: shorter wavelengths scatter far more than longer ones.
Choose, solve, check, then try a fresh question.
Before calculating, read the method prompt and name the condition that makes it useful. Write your own attempt. Open the steps only when you need them, and use the check to catch a wrong sign, unit or interpretation. Finish with the fresh question before reading its answer.
Range of a normal eye
Choose the method: Quote the chapter values: near point and far point.
EZT practice question
What is the range of clear vision for a normal human eye?
Show the worked solution
- The near point is about 25 cm for a young adult.
- The far point is at infinity.
Answer: A normal eye sees clearly from about 25 cm to infinity.
Check: Holding a book closer than about 25 cm strains the eye - that matches the near point.
Watch for this: Do not say the near point is zero; below about 25 cm the lens cannot accommodate enough.
Now try it yourself
What is the power of accommodation?
Check your answer
The ability of the ciliary muscles to adjust the eye lens to focus near and distant objects.
That adjustment is what keeps both near and far vision sharp.
Correct myopia with a concave lens
Choose the method: The correcting lens forms the image of a distant object at the person's far point.
EZT practice question
A myopic person has a far point of 80 cm. Find the focal length and power of the correcting lens.
Show the worked solution
- A distant object (u at infinity) must image at the far point, so f = -80 cm.
- P = 1/f with f in metres: 1/(-0.8).
Answer: f = -80 cm, so P = -1.25 D: a concave lens.
Check: Myopia is corrected with a concave (negative-power) lens, and -1.25 D is negative.
Watch for this: Do not convert 80 cm as 0.8 m and then drop the minus sign; the sign carries the lens type.
Now try it yourself
Find the power needed for a far point of 50 cm.
Check your answer
P = -2 D.
f = -50 cm = -0.5 m, and 1/(-0.5) = -2.
Convert focal length to power
Choose the method: P = 1/f with f in metres.
EZT practice question
Find the power of lenses with f = -2 m and f = +50 cm.
Show the worked solution
- For f = -2 m: P = 1/(-2).
- For f = +50 cm = 0.5 m: P = 1/0.5.
Answer: -0.5 D and +2 D.
Check: The concave lens takes the negative power and the convex lens the positive one.
Watch for this: Do not leave f in centimetres inside P = 1/f; the answer is wrong by a factor of 100.
Now try it yourself
A myopic person has a far point of 1 m. What power is needed?
Check your answer
P = -1 D.
f = -1 m, so P = 1/(-1) = -1 D.
Tell myopia from hypermetropia
Choose the method: Ask where the image falls and which lens pulls it back onto the retina.
EZT practice question
A person sees distant objects clearly but cannot read a book at 25 cm. Name the defect and the correcting lens.
Show the worked solution
- Near objects focus behind the retina - that is hypermetropia.
- A convex lens adds the converging power the eye lacks.
Answer: Hypermetropia (far-sightedness), corrected with a convex lens.
Check: Myopia is the opposite: distant objects blur and a concave lens corrects it.
Watch for this: Do not swap the lenses; concave for myopia, convex for hypermetropia.
Now try it yourself
Which defect needs a concave lens?
Check your answer
Myopia (near-sightedness).
The concave lens diverges light so the image moves back onto the retina.
Trace light through a prism
Choose the method: The ray bends toward the base at both faces.
EZT practice question
A ray passes through a glass prism. Toward which part of the prism does it bend, and why?
Show the worked solution
- At the first face the ray enters denser glass and bends toward the normal.
- At the second face it bends away from the normal.
- Both bends turn the ray toward the base.
Answer: The emergent ray bends toward the base of the prism.
Check: The angle between the incident ray extended and the emergent ray is the angle of deviation.
Watch for this: Do not draw the emergent ray parallel to the base; the bend is toward the base.
Now try it yourself
Does light speed up or slow down inside the prism?
Check your answer
It slows down; glass is optically denser than air.
Refraction happens because the speed of light changes between media.
Explain dispersion
Choose the method: Different colours refract by different amounts.
EZT practice question
White light passes through a prism and splits into colours. Which colour bends the most, and what is this splitting called?
Show the worked solution
- The splitting of white light into its colours is dispersion.
- Violet refracts the most and red the least.
Answer: Dispersion; violet bends the most (VIBGYOR order, violet to red).
Check: The band of colours produced is the spectrum.
Watch for this: Do not say red bends the most; the order is fixed, violet first.
Now try it yourself
Name the colours of the spectrum in order.
Check your answer
Violet, indigo, blue, green, yellow, orange, red.
The acronym VIBGYOR lists them from most-bent to least-bent.
Use atmospheric refraction
Choose the method: Layers of air at different densities bend starlight and sunlight.
EZT practice question
Why do stars twinkle but planets do not?
Show the worked solution
- Starlight passes through air layers of changing density, so its apparent position keeps shifting.
- Stars are point sources, so the shifting shows as twinkling.
- Planets are extended sources; the shifts average out.
Answer: Stars are point sources, so atmospheric refraction makes their light flicker; planets are extended, so the effects average out.
Check: The same refraction advances sunrise and delays sunset by about two minutes each.
Watch for this: Do not attribute twinkling to the star itself; the atmosphere does it.
Now try it yourself
Why is the Sun visible a little before actual sunrise?
Check your answer
Atmospheric refraction bends sunlight toward us before the Sun crosses the horizon.
The denser lower layers curve the light path down to the observer.
Explain scattering and the blue sky
Choose the method: Shorter wavelengths scatter far more strongly.
EZT practice question
Why does the clear sky look blue?
Show the worked solution
- Air molecules scatter sunlight.
- Blue light has a shorter wavelength and scatters far more than red.
- Scattered blue reaches the eye from every direction.
Answer: Air molecules scatter the shorter blue wavelengths the most, so blue light reaches us from all over the sky.
Check: At sunrise and sunset the long path through air removes blue, leaving the Sun red - consistent.
Watch for this: Do not say the sky reflects the ocean; scattering by air molecules is the reason.
Now try it yourself
What is the Tyndall effect?
Check your answer
The scattering of light by colloidal particles, which makes the light path visible.
The same scattering idea, seen in a colloid rather than the open sky.
Try a mixed set
Choose a method or explanation before opening each answer.
1. Near point of a normal eye?
Show answer and reason
About 25 cm.
Closer than that, the eye lens cannot accommodate enough.
2. Which lens corrects myopia?
Show answer and reason
A concave lens.
It diverges light so the image moves back onto the retina.
3. Which colour deviates the most in a prism?
Show answer and reason
Violet.
Shorter wavelengths refract more strongly.
4. Why is the sky blue?
Show answer and reason
Air molecules scatter the shorter blue wavelengths the most.
Scattering strength falls steeply as wavelength grows.
Try it yourself
Work these on paper before checking any notes. Answers are deliberately not shown here.
- A myopic person has a far point of 50 cm. Find the power of the correcting lens.
- A myopic person has a far point of 1 m. Find the power of the correcting lens.
- State the near point and far point of a normal human eye.
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Questions about this practice page
- What causes myopia and hypermetropia?
- In myopia the eye focuses distant objects in front of the retina (eyeball too long or lens too strong). In hypermetropia near objects focus behind the retina (eyeball too short or lens too weak).
- Why is the sky blue?
- Air molecules scatter sunlight, and the shorter blue wavelengths scatter far more than the longer red ones, so blue reaches the eye from every direction.
- Why does a prism produce a spectrum?
- Each colour in white light refracts by a different amount - violet the most, red the least - so the colours separate. This is dispersion.
- What is the power of accommodation?
- The eye's ability to adjust its lens, through the ciliary muscles, to focus both near and distant objects.
- Are these the NCERT exercise questions for The Human Eye and the Colourful World (Class 10)?
- No. EZT pages are original practice following the chapter's section order - use them to prepare for the textbook exercises, not as a substitute for your book.