The Human Eye and Colourful World : Complete Set of Questions

This set of questions contains all the possible concepts
which could be asked in the examination

The Human Eye 

Q.1 Draw a neat labelled diagram of human eye and explain the function of each part

The main parts of the human eye are -

• Cornea- Front part of the eye bulging outwards

• Iris- It controls the amount of light entering in the eye, by varying the size of the pupil.

• Pupil- It is the central hole in the iris

• Ciliary muscles- These muscles hold the eye in position

• Eye lens- It is a crystalline lens made of transparent material. Its curvature and focal length can be changed by ciliary muscles.

• Aqueous humour- Liquid filling the space between cornea and eye lens.

• Retina- It is light sensitive screen on which the image is formed

• Vitreous humour- It is transparent liquid filling the space between eye lens and cormnea.

• Optic nerve- These carry electrical signal to the brain

• Blind spot- A raised point on the retina which is insensitive to light

• Optic nerve-Line passing through the centre of the eye lens and cornea.

Q.2 Why is blind spot so called?

The image formed at this point is not sent to the brain.

Q.3 Explain the working of the human eye:

The light coming from an object enters the eye through the cornea and the pupil

The crystalline lens focuses these light rays to form a real, inverted and highly diminished image on the retina.

When the light rays fall on the sensory cells (rods and cones), they get activated upon illumination and generate electrical signals.

These electrical signals are then sent to the brain by the optic nerve.

The brain interprets the signals and renders the erect image of the object.

Q.4 Define ‘power of accommodation of the eye’?

The process by which the ciliary muscles change the focal length of an eye lens to focus distant or near objects clearly on the retina is called the accommodation of the eye. 

Q.5 How does an eye focus objects at varying distances?
To focus on distant objects the ciliary muscles relax making the eye lens thin.
As a result the focal length of the eye lens increases and we see the distant objects.
But to focus on nearby objects, the ciliary muscles contract making the eye lens thick. As a result the focal length of the eye lens decreases and we see the nearby objects.
In short, it is the adjustment of the focal length of the eye lens which enables us to focus on objects situated at different distances.

Q.6 What is meant by near point and far point?

Near Point: Near point or least distance of distinct vision is the point nearest to the eye at which an object is visible distinctly.
For a normal eye the least distance of distinct vision is about 25 centimetres.
However, it varies with age of the person. For example, for infants it is only 5 to 8 cm.

Far Point : Far point of the eye is the maximum distance up to which the normal eye can see things clearly. It is infinity for a normal eye.

Q.7 Define Range of Vision

The distance between the near point and the far point is called the range of vision

Q.8 What is meant by Persistence of vision?

The image of an object seen persists on the retina for 1/16 second even after the removal of the object. This continuance of sensation of eye for some timed is called persistence of vision.

Q.9 The image formed on the retina is inverted. Then, why do we see an erect image of our surroundings?

When the brain interprets the image, it again inverts the image formed on the retina, to make the objects visible in the same way as they are in our surroundings.

Q.10 How is the focal length of eye lens changed?
The focal length of eye lens is changed by changing of the curvature of the eye lens by ciliary muscles.

When the ciliary muscles relax, the lens becomes thin and its focal length increases.

When the ciliary muscles contract, the curvature of the lens increases and its focal length decreases. 


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