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Class 10 Science (Human Eye and The Colorful World)
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KEEP IT UP COACHING POINT“Obstacles are what you see when you take your eyes off the goal”
THE HUMAN EYE AND THE
COLOURFUL WORLD
The human eye is one of the most valuable and sensitive sense organs which enable us to see objects
through its convex lens by using refraction property of light. The main parts of the human eye are:
1) Cornea: --- The transparent spherical membrane covering the front of the eye is known as cornea.
2) The Iris: ---- The coloured diaphragm between the cornea and the lens is iris. The iris is situated just
behind the cornea. It controls the size of the pupil.
3) Pupil: ----- The middle point of the iris has a hole, which is called pupil. The pupil appears black
because
no light is reflected from it. It regulates and controls the amount of light entering the eye.
4) Eye Lens: --- Transparent crystalline lens, composed of fibrous---jelly like material, convex in nature.
5) Accommodation:--- The ability of the eye lens to see far and near objects by adjusting its focal length
is called the accommodation of the eye. The ciliary muscles can modify the curvature of the lens.
Relaxation of ciliary muscles →Lens becomes thin – increase in focal length. Able to see distant objects.
Contraction of ciliary muscles→Lens becomes thick – focal length decreases. Able to see near objects.
6) Retina: -- The screen on which image is formed by the lens system of human eye is called Retina .The
retina is a delicate membrane having enormous number of light sensitive cells called rods and cones
cells.
7) Rods: --- Respond to the less intensity of light, enables us to see in dim light, cannot distinguish
between various colours.
8) Cones: -- Respond to colour by generating electrical impulses. The light sensitive cells get activated
upon illumination and generate electrical signals, which are sent to the brain via the optic nerves. The brain
interprets these signals and finally processes the information so that we perceive objects as they are.
Power of Accommodation of the Eye:→ Process of altering the focal length of the eye lens by the ciliary
muscles to focus nearer or distant objects on the retina is called the Power of Accommodation of the Eye.
Q 1 ) Write the role of Ciliary muscles?
Ans) (1) To focus distant objects→ Ciliary muscles are relaxed and pulled outwards. Due to this eye lens
becomes flattened, hence focal length increases
(2) To focus near by objects→ Ciliary muscles are contracted and pulled inwards. Due to this lens
becomes bulging, hence focal length decreases.
Q2) a) Define an eye?
b) Draw a well labelled diagram of human eye.
c) Name the part of human eye:--
____________________________________________________________________________
C-162, Govindpura Kardhani, Kalwar Road, Jhotwara, Jaipur-302012
Cell: 9649978593, 9782830493, 8890497070
, KEEP IT UP COACHING POINT
“Obstacles are what you see when you take your eyes off the goal”
1. Provides protection to eye→ Cornea.
2. Which regulates amount of light entering into the eye→ Iris.
3. The opening of iris/ diaphragm through which light enters→Pupil.
4. Screen of human eye on which image is formed→ Retina.
5. The point on retina where image is not formed→ Blind spot.
6. The nerve which transmits electric sign of image from retina to brain→ Optic Nerve.
7. The part/ muscles which adjust focal length of lens→ Ciliary Muscles.
8. Two kinds of jelly like fluids which provide lubrication to eye→ Aqueous Humour ,Vitreous
Humour.
d) What is the nature of lens found in human eye?
→ Converging.
e) What happens to image distance in human eye?
→ It is fixed.
Q3) Write the role of the following in human eye→
1. Iris
2. Pupil
3. Ciliary Muscles
4. Optic Nerve
5. Retina .
Near Point:-→
1) The minimum distance at which objects can be seen most distinctly without any strain is called near
point.
2) It is also known as least distance of distinct vision
3) It is 25 cm for a normal eye.
Far Point:-→
1) The farthest distance up to which the eye can see things clearly without any strain.
2) For normal eye it is infinity.
Range Of Vision:→
1) The distance between near point and far point is called range of vision.
2) It is 25cm to infinity for normal human eye.
Q4) How image is formed on retina?
Ans) 1) The light rays coming from the object enter the pupil of the eye and fall on the eye lens.
2) The eye lens is a convex lens so it is a converging lens and converges the light rays and produces a real
and inverted image of the object on the retina.
3) The image formed on the retina is sent (conveyed) to the brain by the optic nerve and gives rise to the
sensation of vision.
4) The retina has large number of light sensitive cells, when the image is formed on the retina these light
sensitive cells get activated and generate electrical signal/ impulses.
5) The retina sends the electrical signals to the brain through optic nerve.
6) Although the image formed on the retina is inverted, our brain interprets the image as that of an erect
object.
Q5) What is Blind Spot?
Ans) A very small region of the retina where the optic nerve enters the eye ball is insensitive to light and
known as Blind Spot. Since it is insensitive to light, no image formation takes place on it.
Q6) Which part of the eye controls the amount of light entering the eye?
Ans) Iris regulates the amount of light entering the eye by adjusting the size of pupil . So it is iris which
reduces or increases the size of pupil and finally pupil regulates the amount of light entering the eye.
Q7) Human eye is like a camera. How?
Ans) The human eye is like a camera because eye lens of our eye is a convex lens and forms a real and
inverted image of the object on the light sensitive screen called retina same as in a camera where the
convex lens forms a real and inverted image of the object on the light sensitive photographic film.
____________________________________________________________________________
C-162, Govindpura Kardhani, Kalwar Road, Jhotwara, Jaipur-302012
Cell: 9649978593, 9782830493, 8890497070
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