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CBSE Questions for Class 10 Physics Human Eye And Colorful World Quiz 1 - MCQExams.com
CBSE
Class 10 Physics
Human Eye And Colorful World
Quiz 1
The change that occurs in the eye to see the distant objects cleary is
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Focal length of the eye lens decreases
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Curvature of the eye lens increases
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Focal length of the eye lens increases
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Culinary muscles of the eye contract
Explanation
The human eye lens has the ability to adjust its focal length based on the distance of the object. In order to see the distant object clearly, the lens adjust itself to increase its focal length.
The least distance of distinct vision for a young adult with normal vision is
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$$ 25 \mathrm{m} $$
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$$ 20 \mathrm{m} $$
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$$ 25 \mathrm{cm} $$
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$$ 20 \mathrm{cm} $$
Explanation
The least distance of distinct vision for a normal person is $$ 25 \mathrm{cm} $$.
A person is suffering from 'presbyopia' ( myopia and hyper metropia both defects ) should use
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A concave lens
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A convex lens
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A bifocal lens whose lower portion is convex
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A bifocal lens whose upper portion is convex
Explanation
A bifocal lens consists of both convex lenses with lower part is convex.
A person can see clearly object only when they lie between 50 cm and 400 cm from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens, the person has to use, will be :
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Convex, + 0.15 D
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Convex, +2.25 D
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Concave, -0.25 D
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Convex, + 0.2 D
Explanation
Image distance, $$v=-4\ m$$
We know that: $$\dfrac{1}{-4}-\dfrac{1}{\infty}=\dfrac{1}{d}$$
$$\Rightarrow P=\dfrac{1}{d}=-0.25 $$ D
It is a concave lens.
A far sighted person has his near point 50 cm. Find the power of lens he should use to see at 25 cm clearly.
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+1 D
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+2 D
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-2 D
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-1 D
Explanation
In order for a person to see the object at 25cm clearly, the lens should make an image of the object at 25cm distance at a distance of 50 cm.
Hence, $$u=-25cm=-0.25m$$
$$v=-50cm=-0.5m$$
Thus, Power $$=\dfrac{1}{f}=\dfrac{1}{v}-\dfrac{1}{u}=-2D+4D=+2D$$
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Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
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Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
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Assertion is correct but Reason is incorrect.
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Both Assertion and Reason are incorrect.
Explanation
When white light falls on the compact disc, the light gets split into multiple colours. The CD acts as a prism here. Due to different refractive indices for different colours. Thus they get refracted at different angles and multiple colours are visible.
Therefore, both Assertion and Reason are correct and the Reason is the correct explanation for assertion.
For a person near point of vision is $$100\ cm$$. Then the power of lens he must wear so as to have normal vision, should be:
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$$+1\ D$$
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$$-1\ D$$
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$$+3\ D$$
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$$-3\ D$$
Explanation
For normal vision, $$u =-25$$ cm
Given : $$v = -100$$ cm
Using lens formula
$$\dfrac{1}{v} - \dfrac{1}{u} = \dfrac{1}{f}$$
$$\dfrac{1}{-100} - \dfrac{1}{-25} = \dfrac{1}{f}$$ $$\implies f =+ \dfrac{100}{3}$$ cm $$ =+ \dfrac{1}{3}$$ m
Power of the lens used $$P = \dfrac{1}{f}$$ where $$f$$ is in meter
$$\therefore$$ $$P = +3$$ $$D$$
When Astronauts fly at higher altitude, the sky appears dark because ;
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Scattering of light does not take place.
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Scattering of light takes place.
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Refraction of light takes place.
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Dispersion of light takes place.
Explanation
When sunlight passes through the atmosphere, the fine particles in the air scatter the blue color (shorter wavelengths) more strongly than red. The scattered blue light enters our eyes.
When Astronauts fly at higher altitudes, the sky appears dark because, at very high altitudes, there is no atmosphere. So, there would not have been any scattering of light.
When white light is passed through an upside down (inverted) prism then ................
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White light is obtained
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Spectrum is obtained with violet colour undergoing maximum and red colour undergoing minimum deviation
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Spectrum is obtained with red colour undergoing maximum deviation and violet colour undergoing minimum deviation.
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Light gets blocked
Explanation
Here violet undergoes minimum deviation and red undergoes maximum deviation.
Focal length of human eye lens is about _____________.
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2.5 m
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2.5 cm
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2.5 mm
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25 cm
Explanation
The focal length of the human eye lens is 2.5 cm.
A myopic person cannot see distinctly , objects that are :
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near
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far
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Neither
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horizontal and vertical signs
Explanation
Myopia is a vision defect in which a person can see nearby objects clearly but is not able to see distinct objects clearly. In this defect, the rays coming from distant objects, focus in front of retina, instead of on retina.
When objects at different distances are seen by the eye, which of the following remains constant?
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The focal length of the eye lens
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The object distance from the eye lens
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The radii of curvature of the eye lens
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The image distance from the eye lens
Explanation
In the eye, image is always formed at retina which is at a fixed distance in eye. So, when objects at different distances are seen by the eye, the image distance from the eye lens remains constant by changing radii of curative of the eye lens leading to change in focal length. As objects are at different distances, object distance from eye lens changes.
Myopia occurs due to:
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Increase in the focal length of eye lens
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Decrease in the distance between retina and lens
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Decrease in the focal length of the eye lens
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Increase in the distance between retina and lens
Explanation
Myopia is the term used to define short sightedness. Light from a distant object forms an image before it reaches the retina. This is because the eye ball is too large, or the cornea or crystalline lens is too strong. This results in
decrease in focal length of eye lens, whereas the distance between retina and lens is always constant.
The focal length of a normal eye-lens is about:
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$$1\ mm$$
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$$2\ cm$$
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$$25\ cm$$
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$$1\ m$$
Explanation
The focal length of a normal eye lens is about $$2\ cm$$ because distance between eye lens and retina is approximately $$2\ cm$$. So, when parallel rays are coming they form image at focus and to make image at retina focal length should be about $$2\ cm$$.
The power of lens in the spectacles of a person is $$+2D$$. The person suffers from :
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Hypermetropia
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Myopia
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Color blindness
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Presbyopia
Explanation
As power is $$+2D$$, therefore focal length is $$= \dfrac{1}{P}$$
which is $$+\dfrac{1}{2}m=+50cm$$ so, focal length is positive which is for convex lens and a convex lens is used for correction of hypermetropia. So, the person is suffering from hypermetropia, hence correct option is $$A$$.
Inability of the eye to focus on both far and near objects with advancing age is:
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Astigmatism
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Presbyopia
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Myopia
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Hypermetropia
Explanation
With advancing age when ciliary muscles become weak and are not able to strain enough to reduce focal length to appropriate value then this defect is known as presbyopia.
For a myopic (short-sighted) eye, rays from far distant objects are brought to focus at a point:
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on the retina
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behind the retina
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in between eye lens and retina
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at any position
Explanation
In a myopic eye, rays from distant objects are brought to focus at a point in between eye lens and retina. A myopic person can not see distance objects clearly, but is able to see nearby objects clearly.
The ability of eye to focus on both near and far objects is called:
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Presbyopia
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Myopia
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Hypermetropia
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Power of accommodation
Explanation
The ability of the eye lens to adjust its focal length
is called as power of accommodation. It helps us to see both near and distant objects clearly. Thus, option $$D$$ is correct.
Hypermetropia is a synonym for:
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Far-sightedness
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Near-sightedness
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Bad vision due to old age
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None of these
Explanation
Hypermetropia is also known as far-sightedness. A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly.
Myopia is also known as near-sightedness. A person with myopia can see nearby objects clearly but cannot see distant objects distinctly.
The power of accommodation of the eye usually decreases with aging.
In the case of hypermetropia:
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the image of a near object is formed behind the retina
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the image of a distant object is formed in front of the retina
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a concave lens should be used for correction
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a bifocal lens should be used for correction
Explanation
In hypermetropia image of a distance object is formed on the retina and image of a near object is formed behind the retina. For correction of hypermetropia , convex lens is used.
A myopic person can not see objects lying beyond 2m. The focal length and power of the lens required to remove this defect will be?
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1m and 0.5D
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-2m and -0.5D
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0.5m and 0.5D
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-0.5, and 0.5D
Explanation
$$u=+2m$$
$$v= \infty $$
$$\dfrac{1}{v}-\dfrac{1}{u}=\dfrac{1}{f}$$
$$\dfrac{1}{\infty }-\dfrac{1}{2}=\dfrac{1}{f}$$
$$f= -2m$$
$$P= \dfrac{1}{f}$$
$$= \dfrac{1}{-2}$$
$$= -0.5 D$$
The power of lens, a short sighted person uses is $$- 2 \ D$$. The maximum distance of an object which he can see without spectacles is
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$$25 \ cm$$
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$$50\ cm$$
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$$100\ cm$$
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$$10\ cm$$
Explanation
The maximum distance of an object, which a person can see without spectacles is equal to the focal length of the lens.
Hence, let $$ focal \ length = f$$
$$Power = P = -2 \ D$$
$$f= \dfrac{100}{P}$$,
$$= \dfrac{100}{-2}cm$$
$$= -50\ cm$$
So he can see upto a distance of $$50 \ cm$$, without spectacles.
What happens when
white light passes through a glass prism?
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Light dispersion and formation of a 7 colors spectrum.
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Light dispersion and formation of a 6 colors spectrum.
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Light reflection and a formation of a 6 colors spectrum.
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Light reflection and a formation of a 7 colors spectrum.
Explanation
Upon passage through the prism, the white light is separated into its component colors - red, orange, yellow, green, blue, indigo and violet.
A long sighted person has a least distance of distinct vision of 50 cm. He wants to reduce it to 25 cm. He should use a :
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Concave lens of focal length 50 cm
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Convex of focal length 25 cm
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Convex lens of focal length 50 cm
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Concave lens of focal length 25 cm
Explanation
Given, $$u= \infty $$
Image distance, $$v= 50cm$$
From lens formula, $$\dfrac{1}{v}-\dfrac{1}{u}= \dfrac{1}{f}$$
$$\dfrac{1}{50}-\dfrac{1}{\infty }= \dfrac{1}{f}$$
$$f= +50\ cm$$
He should use a convex lens of focal length 50 cm.
How are we able to see both the nearby and the distant objects clearly?
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By changing the focal length of the eye lens.
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By changing the size of the eye lens.
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By changing the power of the eye lens.
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None of these.
Explanation
Human eye is able to see nearby and distant objects clearly by changing the focal length of the eye lens, This availability of eyes is called power of accommodation. Thus, option $$A$$ is correct.
When light rays enter the eye, most of the refraction occurs at the:
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Crystalline lens
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Outer surface of the cornea
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Iris
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Pupil
Explanation
Cornea is the transparent spherical part of the eye covering the iris and pupil. When an object appears in front of the eye, the rays from the object enter through this transparent cornea and refraction occurs at the outer surface. thus, option $$B$$ is correct.
The far point of a myopic eye is 250 cm. The correcting lens should be a
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diverging lens of focal length 250 cm
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converging lens of focal length 250 cm
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diverging lens of focal length 125 cm
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converging lens of focal length 125 cm
Explanation
$$u = -\infty $$
$$ v = -250 cm$$
$$\dfrac{1}{v}-\dfrac{1}{u}= \dfrac{1}{f}$$
$$(-\dfrac{1}{\infty}-\dfrac{1}{250})= \dfrac{1}{f}$$
$$f= -250cm$$
The correcting lens of focal length $$250 cm$$, since myopic eye is corrected by using a concave lens (which is a diverging lens) of suitable power, thus option $$A$$ is correct.
What are the colours of the Sun observed most during sunrise/sunset and noon?
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white and red
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reddish and orange
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yellow and reddish
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orange and blue
Explanation
During sunrise and sunset the sun rays have to pass through a larger distance and also a greater thickness of air since it is low in the sky. At these positions, the sky looks orange-red colour because photons of red and orange light are least scattered through the atmosphere and are able to reach our eyes.
A man cannot see clearly the objects beyond a distance of 20 cm from his eyes. To see distant objects clearly the kind of lenses and its focal length must be
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100 cm concave
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100 cm convex
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20 cm convex
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20 cm concave
Explanation
$$u= +20cm$$
$$v= \infty $$
$$\dfrac{1}{v}-\dfrac{1}{u}= \dfrac{1}{f}$$
$$\dfrac{1}{\infty }-\dfrac{1}{+20}= \dfrac{1}{f}$$
$$f=-20\ cm$$
A hollow glass prism gives
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a dim spectrum
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bright spectrum
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no spectrum
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only continuous spectrum
Explanation
A hollow glass prism does not give any spectrum because it does not have any medium inside it is hollow from inside so white light can not split in vacuum because in vacuum all colors light travel with same speed hence they do not split and no spectrum is observed.
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