Class X Science / Human eye

Class X Science

Notes for Human eye

Class X Science
NCERT Solution for Human Eye and Colourful World

NCERT IN-TEXT ACTIVITIES SOLVED

Q1.   What is meant by power of accommodation of the eye?

Ans. The ability of the eye to focus the distant objects as well as the nearby objects on the retina by changing the focal length of the eye lens is called power of accommodation.

Q2.   A person with a myopic eye cannot see objects beyond 1.2 m distincti What should be the type of the corrective lens used to restore proper vision?

Ans. A person with a myopic eye can use concave lens to restore proper vision.

Q3.   What is the far point and near point of the human eye with normal vision?

Ans. The far point is infinity and the near point is 25 cm of the human eye with normal vision.

Q4.   A student has difficulty reading the blackboard while sitting in the It row. What could be the defect the child is suffering from? How can it be corrected?

Ans. A student is suffering with the eye defect named myopia, in this defect person can see nearby objects clearly but cannot see far off objects distinctly. It can be corrected by using concave lens.

QUESTION FROM NCERT TEXTBOOK

Q1.   The human eye can focus objects at different distances by adjusting the focal length of the eye lens. This is due to

           (a) presbyopia                                  (b) accommodation

           (c) near-sightedness                      (d) far-sightedness

Ans. (b) accommodation

Q2.   The human eye forms the image of an object at its

           (a) cornea.           (b) iris.

           (c) pupil.              (d) retina.

Ans. (d) retina.

Q3.   The least distance of distinct vision for a young adult with normal vision is about

           (a) 25 m.           (b) 2.5 cm.

           (c) 25 cm.           (d) 2.5 m.

Ans. (a) 25 cm

Q4.   The change in focal length of an eye tens is caused by the action of the

           (a) pupil.                                 (b) retina.

           (c) ciliary muscles.           (d) iris.

Ans. (c) ciliary muscles.

Q5.   A person needs a lens of power �5.5 dioptres for correcting his distant vision. For correcting his near vision he needs ae s of power +1.5 dioptre. What i the focal length of the lens required for correcting (i) distant vision, and (ii) near viion?

Ans. The focal length of a lens is given by

           

Q6.   The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?

Ans. For the myopic eye

           

Q7.   Make a diagram to show how hypermetropia is corrected. The near point of a hypermerropic eye is I m. What is the power of the lens required to coma this defect? Assume that the near point of the normal eye is 25 cm.

Ans.Ans.

           (a) The hyperinetropic eye, and (b) correction for hypermetropia with a convex lens

           

Q8.   Why i a normal eye not able to see clearly the objects placed closer than 25 cm?

Ans. Ciliary muscles can contract the lens of human eye to a certain limit because of which a person with normal vision can see the nearby objects clearly only if placed at 25 cm but if the object is placed closer to the eye than it cannot see the objects clearly:

Q9.   What happens to the image distance in the eye when we increase the distance of an object from the eye?

Ans. The image distance in the eye remains the same. On increasing the distance of an object from the eye, the focal length of the eyes changes due to ciliary muscles which helps an eye to focus the object image on retina.

Q10.   Why do stars twinkle?

Ans. Stars twinkle due to atmospheric refraction of light from the stars and changing density of air around the earth.

Q11.   Explain why the planets do not twinkle.

Ans. Planets are much closer to earth and behave like extended source.

Q12.   Why does the sun appear reddish early in the morning?

Ans. When the sun rises early in the morning (or set in the evening), the light from sun travels through the thicker layer of air and larger distance of the atmosphere surrounding the earth. PIence the blue light scatters the most but red light does not scatters and reaches our eyes.

Q13.   Why does the sky appear dark instead of blue to an astronaut?

Ans. In space there are no particles, air, gases, water droplets etc., present to scatter the light. So when the astronauts look at the sky in the space, there is no light entering our eyes, hence it appears dark.

HUMAN EYE AND COLORFUL WORLD

MULTIPLE CHPOICE QUESTIONS

1.   The image formed by retina of human eye is

       a.  Virtual and erect

       b.  Real and inverted

       c.  Virtual and inverted

       d.  Real and erect

2.   The change in the focal length of human eye is caused due to

       a.  Ciliary muscles

       b.  Pupil

       c.  Cornea

       d.  Iris

3.   The least distance of distinct vision for a young adult with normal vision is

       a.  25 m

       b.  20 m

       c.  25 cm

       d.  20 cm

4.   The persistence of vision for human eye is

       a.  1/10th of a second

       b.  1/16th of a second

       c.  1/6th of the second

       d.  1/18th of a second

5.   The light sensitive cell present on retina and is sensitive to the intensity of light is:

       a.  Cones

       b.  Rods

       c.  Both rods and cones

       d.  None of these

6.   The phenomena of light responsible for the working of the human eye is

       a.  Reflection

       b.  Refraction

       c.  Power of accommodation

       d.  Persistence of vision

7.   Which of the following colors is least scattered by fog, dust of smoke?

       a.  Violet

       b.  Blue

       c.  Red

       d.  Yellow

8.   The colored light that refracts most while passing through a prism is

       a.  Yellow

       b.  Violet

       c.  Blue

       d.  Red

9.   The amount of light entering the human eye is controlled by

       a.  Ciliary muscles

       b.  Pupil

       c.  Cornea

       d.  Iris

10.   The part of the eyes refracts light entering the eye from external objects?

          a.  Lens

          b.  Cornea

          c.  Iris

          d.  Pupil

ANSWERS

1.    B

2.    A

3.    C

4.    B

5.    B

6.    B

7.    C

8.    B

9.    B

10. B

HUMAN EYE AND COLORFUL WORLD

PREVIOUS YEAR QUESTIONS

1.   What eye defect is hypermetropia? Describe with a ray diagram how this defect of vision can be corrected by using an appropriate lens. (CBSE 2011)

2.   A star sometimes appears brighter and some other times fainter. What is this effect called?

       State the reason for this effect. (CBSE 2012)

3.   A student cannot see a chart hanging on a wall placed at a distance of 3 m from him. Name the defect of vision he is suffering from. How can it be corrected? (CBSE 2012)

Draw ray diagrams for the (i) defect of vision and also (ii) for its correction

4.   Why is red color selected for danger signal lights? (CBSE 2008)

5.   (a) A person cannot read newspaper placed nearer than 50 cm from his eyes. Name the defect of vision he is suffering from. Draw a ray diagram to illustrate this defect. List its two possible causes. Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length.

       (b) We see advertisements for eye donation on television or in newspapers. Write the importance of such advertisement. (CBSE 2013)

6.   Explain giving reason why the sky appears blue to an observer from the surface of the earth? What will the color of the sky be for an astronaut staying in the international space station orbiting the earth? Justify your answer giving reason. (CBSE 2013)

7.   (a) List three common refractive defects of vision. Suggest the way of correcting these defects.

       (b) About 45 lac people in the developing countries are suffering from corneal blindness. About 30 lac children below the age of 12 years suffering from this defect can be cured by replacing the defective cornea with the cornea of a donated eye. How and why can students of your age involve themselves to create awareness about this fact among people? (CBSE 2014)

8.   With the help of a labeled diagram, explain why the sun appears reddish at the sun-rise and the sunset. (CBSE 2015)

9.   (a) What is dispersion of white light? What is the cause of this dispersion? Draw a diagram to show the dispersion of white light by a glass prism.

       (b) a glass prism is able to produce a spectrum when white light passes through it but a glass slab does not produce any spectrum. Explain why? (AI CBSE 2008]

HUMAN EYE AND COLORFUL WORLD

HOTS

1.   What is a diameter of human eye?

2.   What is the function of crystalline lens of human eye?

3.   In which type of eye defect far point of the eye gets reduced?

4.   Why do birds fly back to their nest in the evening?

5.   Why do you take time to find object when you enter in dim lighted room from outside in the sun?

6.   Why does ray of light splits when passed from prism?

7.   Why doesn�t planet appear to be twinkling?

8.   Why we can�t see things very close to our eyes?

9.   When we see any object through the hot air over the fire, it appears to be wavy, moving slightly. Explain.

10.   Why does sky appear blue on a clear day?

HUMAN EYE AND COLORFUL WORLD

TEST

Maximum time: 40 minutes

Maximum marks: 23 marks

1.   Name the transparent membrane through which light enters the first in the eyes. (1)

2.   What is the function of iris? (1)

3.   What is persistence of vision? (1)

4.   What is Tyndall effect? (1)

5.   The image formed on retina is inverted but we can see the objects erect. Why? (1)

6.   What is night blindness and color blindness? (2)

7.   Distinguish between presbyopia and hypermyopia (3)

8.   Draw a well labeled diagram of eye. (4)

9.   Draw a labeled diagram of rainbow formation. Also explain the phenomena. (4)

10.   Name three refractive defects of vision with help of diagram. Explain its reasons and correction of these defects. ?(5)