Numerical Problems on Human Eye and Colourful World CBSE Class 10 Science

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Last Updated on August 31, 2024 by XAM CONTENT

Hello students, here you will find numerical problems on human eye and colourful world with answers. These numericals on human eye and colourful world are very useful for students studying in CBSE Class 10 or for anyone who wants to practice some problems on these topics.

Before we start solving the numerical problems, let’s see some important points and formulae. This will help you to solve the problems efficiently.

Important Concept and Formulae

(1) The human eye is the most important optical instrument.

(2) The main parts of the human eye are: cornea, iris, pupil, ciliary muscles, eye lens, retina and optic nerve.

(3) P = 1/f, where f is in metre.

Human Eye and Colourful World Numerical Problems with Answers

Problem 1:

If the focal length of the eye lens is 2 cm while viewing a far away object, then what is the power of lens when an object at normal near point is viewed?

Ans. P = 54 D

Problem 2:

A person needs a lens of power –5.5 dioptre for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?

Ans. (i) f = –18.2 cm (ii) f = 66.67 cm

Problem 3:

(i) Calculate maximum power of accommodation of a person having normal vision.
(ii) A person needs to use glasses for reading newspaper. Identify the defect in her vision and the type of lens she would need to correct it.

Ans.

(i) D = 25 cm, Now, P = l/f = 100/D = 100/25 = 4D. Thus, for a person having normal vision, the power of accommodation is about 4 dioptre.
(ii) Long sightedness, a convex lens.

Problem 4:

A person needs a lens of power–2.5 dioptres for correcting his vision. Name the defect of vision he is suffering from. Which lens will be using for the correction? Also, find the focal length of lens.

Ans.

The person is using a concave lens of power-2.5 D. The person is, therefore, suffering from myopia. He is using a concave lens for correction of eye.
Since P = 1/f,
we have f = 1/P =1/25 = 0.4 m = 40 cm

Problem 5:

A person cannot see the objects distinctly, when placed at a distance less than 50 cm.
(a) Identify the defect of vision.
(b) Give two reasons for this defect.
(c) Calculate the power and nature of the lens he should be using to see clearly the object placed at a distance of 25 cm from his eyes.

Ans.

(a) Hypermetropia.
(b) (i) Either the hyperopic eyeball is too short
or (ii) The ciliary muscle is unable to change the shape of the lens enough to properly focus the image i.e., the focal length of the eye lens is too long.
(c) P = +3 D

Problem 6:

A person needs a lens of power −4.5 D for correction of her vision.
(a) What kind of defect in vision is she suffering from?
(b) What is the focal length of the corrective lens?
(c) What is the nature of the corrective lens?

Ans.

(a) As the power of lens is negative, she must be suffering from myopia

(b) Given,

\begin{aligned}
\text { Power, } P & =-4.5 \mathrm{D} \text {, focal length, } f=\text { ? } \\
P & =\frac{1}{f} \\
\Rightarrow \quad f & =\frac{1}{P}=\frac{1}{-4.5}=-0.222 \mathrm{~m}=-22.2 \mathrm{~cm}
\end{aligned}

(c) The nature of the corrective lens is concave or divergent.

Problem 7:

(i) Calculate maximum power of accommodation of a person having normal vision.
(ii) A person needs to use glasses for reading newspaper. Identify the defect in her vision and the type of lens she would need to correct it.

Ans.

(i) D = 25 cm, Now, P = l/f = 100/D = 100/25 = 4D. Thus, for a person having normal vision, the power of accommodation is about 4 dioptre.
(ii) Long sightedness, a convex lens.

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Frequently Asked Questions (FAQs) on Human Eye and Colourful World Class 10 CBSE

Q1: Why sky appears dark to the passengers flying at high altitudes?

A1: This is due to the absence of atmosphere at high altitudes. As a result, no light reaches the eye after scattering. So, the sky appears to be dark.

Q2: A person suffering from an eye defect uses lenses of power-1 D. Name the defect he is suffering from and the nature of lens used

A2: Myopia, concave lens

Q3: Name the part of the human eye that helps in changing the focal length of the eye lens

A3: Ciliary muscles

Q4: Mention the factor on which scattering of light depends. Why does the sky appear dark in space?

A4: It depends on the presence of atmosphere containing smoke particles, tiny water droplets and suspended particles of dust and molecules of air. When a beam of light strikes such like fine particles, the path of the beam becomes visible. This happens because in space, there are no air molecules to scatter light.

Q5: Name the part of the eye where image is formed by the eye lens. What is the nature of the image formed? How is this image sent to the brain?

A5: The image of the object formed by the eye lens is at the retina of the eye. The image formed on the retina is real and inverted. The image is then sent to the brain with the help of the optic nerve.

Q6: How is the power of eye lens affected for a person suffering from presbyopia?

A6: It reduces.

Q7: What is astigmatism? How is it corrected?

A7: It is that defect of the eye due to which the image of a distant point source of light is formed, not as a point but as a vertical or a horizontal line. It can be corrected by using cylindrical lenses.

Q8: What do you mean by dispersion of light? Why does it take place?

A8: The process of splitting up of white light into seven colours on passing through a transparent medium like a glass prism is called dispersion. It occurs because the angle of refraction for different colours is different when white light passes through the glass prism.

Numerical Problems on Human Eye and Colourful World CBSE Class 10 Science

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