Write scientific reason. Nearsightedness, this defect can be corrected by using spectacles with concave lens. - Science and Technology 1

Answer in Brief

Write scientific reason.

Nearsightedness, this defect can be corrected by using spectacles with concave lens.



  1. Nearsightedness arises due to slight elongation of the eyeball causing an increase in the distance between the eye lens and the retina or due to an increase in the curvature of the cornea and eye lens resulting in increased converging power.
  2. As a result, light from a distant object arriving at the eye-lens gets converged at a point in front of the retina.
  3. When a concave lens of suitable focal length is placed between the eye and object, due to the diverging effect of the concave lens, the image gets focussed on the retina.
    Thus, nearsightedness can be corrected by using spectacles with a concave lens.
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Chapter 7: Lenses - Write scientific reasons


Given below is a diagram showing a defect of human eye. Study it and answer the following questions.

(i) Name the defect shown in the figure.
(ii) Give reason for this defect of eye in human being.
(iii) Name the type of lens used to correct the eye defect.

In a Std. X class out of 40 students 10 students use spectacles, 2 students have positive power and 8 students have negative power of lenses in their spectacles.

Answer the following questions:

(1) What does the negative power indicate?

(2) What does the positive power indicate?

(3) Generally which type of spectacles do most of the students use?

(4) What defect of eyesight do most of the students suffer from?

(5) Give two possible reasons for the above defect.

What is myopia?

Write the importance of ciliary muscles in the human eye. Name the defect of vision that arises due to gradual weakening of the ciliary muscles. What types of lenses are required by the person suffering from this defect to see the objects clearly?

Akshay, sitting in the last row in his class, could not see clearly the words write on the blackboard. When the teacher noticed it, he announced if any student sitting in the front row could volunteer to exchange his seat with Akshay. Salman immediately agreed to exchange his seat with Akshay. He could now see the words written on the blackboard clearly. The teacher thought it fit to send the message to Akshay’s parents advising them to get his eyesight checked.

In the context of the above event, answer the following questions:-

(a) Which defect of vision is Akshay suffering from? Which type of lens is used to correct this defect?

(b) State the values displayed by the teacher and Salman.

(c) In your opinion, in what way can Akshay express his gratitude towards the teacher and Salman?

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?

Explain two possible reasons of myopia. How can it be corrected? Explain with a suitable diagram.

the biological/technical terms for the lens of eye losing flexibility resulting in a kind of long-sightedness in middle aged people.

What is the scientific name of 


What is the scientific name of 


Name the defect of vision which makes the eye-lens cloudy resulting in blurred vision.

Where is the near point of a person suffering from hypermetropia (or long-sightedness)?

Name the defect of vision which can be corrected by a converging lens. Show clearly by a ray diagram how the lens corrects the defect.

An eye has a far point of 2 m. What type of lens in spectacles would be needed to increase the far point to infinity?  Also calculate the power of lens required. Is this eye long-sighted or short-sighted?

Though a woman can see the distant object clearly, she cannot see the nearby objects clearly. She is suffering from the defect of vision called:
(a) long-sight
(b) short-sight
(c) hind-sight
(d) mid-sight

To read a book held at a distance of 25 cm, will she need converging or diverging spectacle lenses?

Name the following:

The eye defect caused due to shortening of the eye ball from front to back.

Differentiate between members of the following pair with reference to what is asked in bracket.

Rods and cones (sensitivity)

Name an old age eye defect. What happens in it?

Explain the terms ‘adaptation’ and ‘accommodation’ with reference to the eye.

Observer the following diagram and answer the questions.
a) Which eye defect is shown in this diagram?
b) What are the possible reasons for this eye defect?
c) How this defect is corrected, write it in brief?

Name the following:
The photosensitive pigment present in the rod cells of the retina.

Name the cells of the retina that are sensitive to colours.

Choose the correct answer : 
Presbyopia is a disease of _____________

Given below is a diagram depicting a defect of the human eye? Study the same and answer the question that follow:

Name the parts labeled 1 to 4.

Given below is a diagram depicting a defect of the human eye? Study the same and answer the question that follow:

Draw a labeled diagram to show how the above mentioned defect is rectified using the lens named above.

Rewrite the following table so as to match second and third column with first column.


Column I
Column II
Column III
(i) Myopia
Old age problem
Bifocal lens
(ii) Presbyopia
Concave lens.

Anuja cannot see the blackboard writing but she can see nearby things.
(a) What is the eye defect she is suffering from?
(b) State the possible reason for her defect.
(c) How is it corrected

Give Reason:

Older people require glasses to read and write.

Draw a neat labeled diagram to show how hypermetropia can be rectified.

Explain the Term: Presbyopia

Explain the Term: Astigmatism

Explain the Term: Cataract

What type of lens is used to correct Hypermetropia?

Complete the following sentence with appropriate word :
An inability to focus on nearby objects due to loss of elasticity of the lens with age is called Iris.

The diagram given below represents the cross-section of the human eye:

(i) Name the parts labeled 1—12.
(ii) What is the function of the part marked ‘10’?
(iii) What would happen if part ‘5’ is damaged or cut?

 Choose the Odd One Out: 

In Myopia the human eye _______.

Due to elongation of _______ and increase in curvature of the eye lens, a person cannot see distant objects clearly.

Nearsightedness: elongated eyeball : : farsightedness: _______

Nearsightedness : concave lens : : farsightedness : _______

Observe the given below the figure, correct it and explain and write about the concept depicted in this figure.

Given below is a diagram showing a defect of vision. Name the defect of vision and draw an accurately labelled diagram to correct this defect.

What are the causes of ‘Myopia’?

Differentiate the eye defects: Myopia and Hypermetropia

Correlate the given sequence:

Hypermetropia : Convex lens : ______ : Concave lens

Observe the figure whether it is correct or not and explain the phenomenon.

Observe the figure and answer the following questions: 

  1. Name the defect of vision represented in the above figure.
  2. State the reasons for this defect.
  3. How is it corrected?
  4. Draw the diagram to show the correction of this defect.

Match the following:

Column - I Column - II
1. Retina a. Path way of light
2. Pupil b. Far point comes closer
3. Ciliary muscles c. near point moves away
4. Myopia d. Screen of the eye
5. Hypermetropia e. Power of accommodation

Complete the following table by observing the given figure:

Figure →
Points ↓
(a) Name of the defect ____________ ____________
(b) Position of the image ____________ ____________
(c) Lens used to correct the defect ____________ ____________


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