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Which part of the human eye controls the amount of light entering into the eyes?

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Important Questions on The Human Eye and the Colourful World

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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
A student is unable to see clearly the words written on the black board placed at a distance of approximately 3 m from him. Name the defect of vision the boy is suffering from. State the possible causes of this defect and explain the method of correcting it.
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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision

Consider the following vision defects listed in Columns I and II and the corrective measures in Column III. Choose the correct combination.

   Column I    Column II    Column III
 P.  Hypermetropia  (i)  Near-sightedness  a.  Convex lens
 Q.  Myopia  (ii)  Far-sightedness  b.  Concave lens
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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
Write the function of cornea of human eye.
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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
What is myopia? How it is corrected?
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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
A student studying the similarities and differences between a camera and the human eye makes the following observations:
I Both the eye and the camera have convex lenses.
IIIn order to focus, the eye lens expands or contracts while the camera lens moves forward or backward.
III The camera lens produces upside down real images while the eye lens produces only upright real images.
IV A screen in camera is equivalent to the retina in the eyes.
V A camera adjusts the amount of light entering in it by adjusting the aperture of the lens. In the eye the cornea controls the amount of light. The correct statements are :
MEDIUM
Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
When do we consider a person to be myopic or hypermetropic? List two causes of hypermetropia. Explain using ray diagrams how the defect associated with hypermetropic eye can be corrected.
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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
Write the function of iris of human eye.
HARD
Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
Draw the ray diagram to show how hypermetropia is corrected.Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is 1 m. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is 0.25 m.
MEDIUM
Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
A person can see clearly object only when they lie between 50 cm to 400 cm from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens, the person has to use, will be
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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
The least distance of distinct vision for a normal eye is
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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
What are the defects of vision? A person needs a lens of power, -5.5 D for correcting his distant vision. For correcting his near vision, he needs a lens of power, +1.5 D. What is the focal length of the lens required for correcting distant vision?
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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
Your friend is having eye sight problem. She is not able to see clearly a distant uniform window mesh and it appears to her as nonuniform and distorted. The doctor diagnosed the problem as :
MEDIUM
Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
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? Why do we have two eyes for vision and not just one?
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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
Write the function of ciliary muscles of human eye.
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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
Why is a normal eye not able to see clearly the objects placed closer than 25 cm?
HARD
Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
Shyam a student has difficulty reading the blackboard while setting in the last row. What could be the defect the child is suffering from? How can it be corrected? Explain with help of appropriate diagram.
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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision

A student sitting on the last bench of a regular classroom is able to see the written work on a blackboard but unable to read from his textbook. Identify the type of defect of vision he is suffering from. What kind of lens should he wear to correct the defect?

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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
A near sighted person has a far point of 20 cm in front of his eye. What is the power of the lens (in dioptres) which will allow this person to see distant objects clearly?
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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
What power should the reading spectacles (lens) have for a person for whom the least distance is 50 cm (in dioptre)
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Science>Physics>The Human Eye and the Colourful World>Human Eyes and Defects of Vision
The change in focal length of an eye-lens is caused by the action of the_____.