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Science questions in details [4 marks ]

Light · Jharkhand Board (JAC) STD 8 (Jharkhand - English Medium). 11 questions.

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questions in details [4 marks ]

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11 questions · self-marked practice — reveal the answer and mark yourself.

Question 14 Marks
State the characteristics of the image formed in a plane mirror.
Answer
Characteristics of the image formed by a plane mirror are:
$-$The images formed by a plane mirror are virtual and erect.
$-$Image formed is of the same size as the object.
$-$Image is laterally inverted.
$-$Image is far behind the mirror as the object is in front of the mirror.
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Question 24 Marks
What is night blindness? What causes night blindness?
Answer
The following factors cause night blindness:
$1.$ The deficiency of Vitamin $A ($retinol$)$ in the diet of a person for a considerable time can lead to the disease called night blindness.
$2.$ The disorder in which the rod cells in the retina gradually lose their ability to respond to the light.
$3.$ It can also happen due to cataract, or clouding of the eye's lens.
$4.$ Usher syndrome can also cause night blindness, which is a genetic condition that affects both hearing and vision.
$5.$ Nearsightedness or blurred vision can also cause night blindness.
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Question 34 Marks
A man stands 10m in front of a large plane mirror. How far must he walk before he is $5m$ away from his image?
Answer
The object distance is equal to image distance in a plane mirror.For the distance of man from his image to be $5m$
The distance of man from mirror + distance of image from the mirror $= 5m$
Since object distance = image distance
Therefore, $2 \times $ distance of man from the mirror $= 5m$
Distance of man from the mirror $=\frac52=2.5\text{m}$
The man is $10m$ from the mirror at the starting, so he will have to walk $10 - 2.5 = 7.5m$ towards the mirror for being 5m away from his image.
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Question 44 Marks
Name the part of the eye:
$a.$ Which controls the amount of light entering the eye.
$b.$ Which converges light rays to form the image.
$c.$ On which image is formed.
$d.$ Which carries the image to brain.
$e.$ Which changes the curvature $($or thickness$)$ of eye$-$lens to focus objects lying at various distances.
Answer
$a.$ Iris controls the amount of light entering the eye by constricting and dilating the pupil in bright and dim light respectively.
$b.$ Lens. The lens may diverge or converge the light rays to form an image.
$c.$ Retina. An upside-down image is formed on the retina.
$d.$ Optic nerve carries the image to brain in form of electric impulses.
$e.$ Ciliary muscle changes the lens shape to focus objects lying at various distances.
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Question 54 Marks
Name the part of the eye:
$a.$ Which controls the amount of light entering the eye.
$b.$ Which converges light rays to form the image.
$c.$ On which image is formed.
$d.$ Which carries the image to brain.
$e.$ Which changes the curvature $($or thickness$)$ of eye$-$lens to focus objects lying at various distances.
Answer
$a.$ Iris controls the amount of light entering the eye by constricting and dilating the pupil in bright and dim light respectively.
$b.$ Lens. The lens may diverge or converge the light rays to form an image.
$c.$ Retina. An upside$-$down image is formed on the retina.
$d.$ Optic nerve carries the image to brain in form of electric impulses.
$e.$ Ciliary muscle changes the lens shape to focus objects lying at various distances.
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Question 64 Marks
Draw a labelled diagram of the human eye. Label the following parts on this diagram: Cornea, Iris, Pupil, Ciliary muscles, Eye-lens, Retina, Optic nerve, Blind spot.
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Question 74 Marks
Explain how you can take care of your eyes.
Answer
One can take care of eyes by following simple steps:
$i.$ Watch television from a distance.
$ii.$ If a dust particle or an insect gets into our eye, we should never rub the eye, instead wash the eye with cold water.
$iii.$ Do not look at the sun directly as too much of light i.e. bright light may injure the retina.
$iv.$ Read from a normal distance of vision.
$v.$ Never read or study in dim light or low light as it causes headaches.
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Question 84 Marks
Which of the following will cause regular reflection of light and which diffuse reflection of light?
$i.$ Polished wooden table.
$ii.$ Chalk powder.
$iii.$ Cardboard.
$iv.$ Mirror.
$v.$ Paper.
$vi.$ Marble floor with water spread over it.
Answer
Polished wooden table: Regular reflection since the surface is polished $($plane$).$
Chalk powder: Diffused reflection will occur because the surface of chalk powder is uneven.
Cardboard: Diffused reflection of light since cardboard has an uneven surface.
Mirror: Regular reflection since the surface of a mirror is plane.
Paper: Diffused reflection since the surface of paper is uneven.
Marble floor with water spread over it: regular reflection as the floor with water will behave as a plane surface.
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Question 94 Marks
Draw a diagram to show the reflection of light from a plane mirror. Label the following on the diagram:
$a.$ Plane mirror.
$b.$ Incident ray.
$c.$ Reflected ray.
$d.$ Point of incidence.
$e.$ Angle of reflection.
$f.$ Normal.
$g.$ Angle of incidence.
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Question 104 Marks
What are the functions of the following parts of the eye?
$i.$ Iris.
$ii.$ Eye$-$lens.
$iii.$ Ciliary muscles.
$iv.$ Retina.
$v.$ Optic nerve.
Answer
Functions of parts:
IRIS: The muscles of the iris dilate and constrict the pupil and thus increases and reduces the amount of light reaching the retina.
EYE-LENS: Lens focuses the light rays passing through it onto the retina and thus creates a clear image of the objects in sight.
CILIARY MUSCLES: The ciliary muscle fibers affect the zonular fibers in eye and thus change the lens shape and thus changes the converging power.
RETINA: Retina receives the light focused by the lens, the photoreceptors In the retina $($rods and cones$)$ convert this light into signals and the signals are then passed onto the brain for viewing.
OPTIC NERVE: The optic nerve transmits signals from photoreceptors in the retina to the brain through electric impulses.
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Question 114 Marks
Write the names of the main parts of the human eye.
Answer
The main parts of the human eye are:
IRIS: The muscles of the iris dilate and constrict the pupil and thus increases and reduces the amount of light reaching the retina.
RETINA: Retina receives the light focused by the lens, the photoreceptors In the retina (rods and cones) convert this light into signals and the signals are then passed onto the brain for viewing.
LENS: Lens focuses the light rays passing through it onto the retina and thus creates a clear image of the objects in sight.
PUPIL: Pupil controls the amount of light that enters the eye. It is controlled by the iris.
CORNEA: Cornea acts as the outermost layer of the eye. It protects the eye with the eyelids.
CILIARY MUSCLES: The ciliary muscle fibers affect the zonular fibers in eye and thus change the lens shape and thus changes the converging power.
OPTIC NERVE: The optic nerve transmits signals from photoreceptors in the retina to the brain through electric impulses.
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