Extra Questions for Class 10th: Ch 11 Human Eye and Colourful World (Science) Important Questions Answer Included

Very Short Answer Questions (VSAQs): 1 Mark

Q1. State one function of iris in human eye.
Function of iris: It controls the size of the pupil.

Q2. Name the part of the eye ?
(i)that controls the amount of light entering into the eye.
(ii) that had real, inverted image of the object formed on it.
(i) Pupil
(ii) Retina

Q3. What is meant by dispersion of light ?
The splitting of light into its component colours is called dispersion of light.

Q4. The sky appears dark instead of blue to an astronaut. State its reason.
The sky appears dark to the astronaut as scattering does not take place at very high attitude due to the absence of atmosphere.

Q5. What is the cause of dispersion of light on passing through a prism ?
The refractive index of the material of a prism is different for different colours of light as different colours have different speed in the material of a prism.

Short Answer Questions-I (SAQs-I): 2 Marks

Q1. What is the cause of dispersion of light on passing through a prism? Which coloured component bends the least during the dispersion of white light through prism ?


The refractive index of the material of a prism is different for different colours of light as different colours have different speed in the material of a prism. Also, prism has non-parallel surfaces.

Q2. Why does it takes some time to see objects in a cinema hall when we just enter the hall from bright sunlight ? Explain in brief.


(a) The pupil regulates and controls the amount of light entering the eye.
(b) In bright sunlight, the size of the pupil is small and when we enter the cinema hall it takes some time for the pupil to expand in size due to dim light.

Q3. How is a normal eye able to see distinctly distant as well as nearer objects ?


Eye lens is made up of fibrous material. Its curvature can be changed by ciliary muscles which changes its focal length.
When muscles are relaxed, the lens becomes thin and focal length increases and the eye is able to see distant objects.
Similarly, when ciliary muscles contract, focal length decreases and eye is able to see nearer objects.

Q4. An old person is unable to see clearly nearby object as well as distant objects : 
(i) What defect of vision is he suffering from ? 
(ii) What kind of lens will be required to see clearly the nearby as well as distant objects ? Give reason.


(i) Presbyopia.
(ii) He shall have to use both kinds of lenses. Convex lens for long sightedness and concave lens for short-sightedness.

Q5.(i) What is the least distance of distinct vision
(ii) How does the thickness of the eye lens change when we shift looking from a distant tree to reading a book ?


(i) It is the minimum distance to which, normal eye can see two similar object distinctly.
(ii) Eye lens will become thicker.

Short Answer Questions-I (SAQs-II): 3 Marks

Q11. Examine this diagram and answer the followed questions.
(a) Name the defect of vision the eye shown in diagram is going through.
(b) Name two reasons for the defect
(c) What type of lens is required to correct this defect of vision?


(a) Hypermetropia
(b) The reasons for this defect are
(i) The focal length of eye lens is increased
(ii) The eye balls become small
(c) A proper convex lens is required to correct this defect of vision.

Q12. (a) What do you mean by far point? What is far point of normal adult human eye?
(b) Name the defect of vision which result in alteration of far point.


(a) The maximum distance at which objects can be seen clearly is known as far point of eye. The far point for normal adult human eye is infinity.
(b) In refraction, we have studied about power of Lens. It is the inverse of focal length. The ability of the eye lens to adjust its focal length/power is called accommodation.

Q13. The near point of hypermetropic eye is 80 cm. What is the nature and power of the lens required to enable him to read a book placed at 25 cm from the eyes?


Near point of hypermetropic eye = 80cm
That means the image of an eye can be seen at 80cm.
Object is at 25cm, which is needed to be seen clear.
So, u =-25cm
So, corrective lens of focal length(f) is needed to show object at 80cm in front of eye.
By the lens formula,
Near point = 80 cm
Object distance u = – 25 cm
ν= – 80 cm (convex lens in case of hypermetropia)
So, the required focal length of lens is 36.36cm.

Q14. What do you mean by atmospheric refraction? When we see any object through the hot air over the fire, it appears to be wavy, moving slightly. Explain.


In a hot weather the air becomes hotter and rises above. The risen hot air is optically rarer than cold air which is optically denser. These there is difference in optical density (or refractive index) between different layers of air. The objects beyond the hot air appears to be wavy because the medium for light to pass through changes, the light passes from denser to rarer and then again to denser medium thereby causing refraction in the air. Moreover the refractive index of the hot air keeps changing which leads to give the wavy appearance of the object.

Long Answer Questions (LAQs): 5 Marks

Q1. What is Tyndall effect ? What is its cause? Explain two phenomena observed in daily life which are based on Tyndall effect.


Tyndall effect : When a beam of light is passed through a colloidal solution, placed in a dark room, the path of beam becomes illuminated when observed through a microscope placed perpendicular to the path of light. This effect is called Tyndall effect.

Cause of Tyndall effect: The size of the colloidal particle is relatively larger than the solute particle of a true solution. The colloidal particles first absorb energy from the incident light and then scatter a part of this energy from their surfaces. Thus, Tyndall effect is due to scattering of light by the colloidal particles and the colloidal particles are seen to be moving as points of light moving against a dark background.

Daily life Examples:
(i) When sunlight passes through a canopy of a dense forest, the tiny water droplets in the mist scatter light and become visible.
(ii) When a fine beam of sunlight enters a smoke filled room through a small hole, the smoke particles become visible due to the scattering of light.

Q2. (a) What is myopia? State the two causes of myopia and with the help of a labelled ray diagrams show:
(i) the eye defect myopia.
(ii) correction of myopia using a lens.
(b) Why is the normal eye unable to focus on an object placed within 10 cm from the eye?


(a) Myopia: Eye can see objects at short distance. Inability of the eye in viewing long distant objects. The image falls before retina.

Causes of Myopia:
(i) Elongation of eye ball.
(ii) Excessive curvature in cornea.
Correction of Myopia: By using concave lens (diverging lens), which shifts the image to the retina by diverging the rays further.
The above diagram represents myopia and its correction via concave lens.

(b) A normal eye is unable to clearly see the objects placed closer than 25 cm because the ciliary muscles of eyes are unable to contract beyond a certain limit.
If the object is placed at a distance less than 25 cm from the eye, then the object appears blurred and produces strain in the eyes.

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