Class 10ScienceThe Human Eye and the Colourful WorldMix Examples - The Human Eye and the Colourful World
MediumWhat are hypermetropia and myopia? What are their causes? How are they rectified?
(N/A) These are common defects of vision.
Hypermetropia (Farsightedness): $A$ person suffering from this defect can see distant objects clearly but cannot see nearby objects clearly. In this defect,the near point of the eye shifts farther away than $25 \ cm$.
Causes:
$1.$ The eyeball becomes too short.
$2.$ The focal length of the eye lens becomes too large.
Correction: This condition is corrected using a converging or convex lens.
Myopia (Nearsightedness): $A$ person suffering from myopia can see nearby objects clearly but cannot see distant objects clearly. In this defect,the far point of the eye comes closer than infinity.
Causes:
$1.$ The eyeball becomes too long.
$2.$ The focal length of the eye lens becomes too small.
Correction: This condition is corrected using a diverging or concave lens.
Hypermetropia (Farsightedness): $A$ person suffering from this defect can see distant objects clearly but cannot see nearby objects clearly. In this defect,the near point of the eye shifts farther away than $25 \ cm$.
Causes:
$1.$ The eyeball becomes too short.
$2.$ The focal length of the eye lens becomes too large.
Correction: This condition is corrected using a converging or convex lens.
Myopia (Nearsightedness): $A$ person suffering from myopia can see nearby objects clearly but cannot see distant objects clearly. In this defect,the far point of the eye comes closer than infinity.
Causes:
$1.$ The eyeball becomes too long.
$2.$ The focal length of the eye lens becomes too small.
Correction: This condition is corrected using a diverging or concave lens.
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$(a)$ Draw ray diagrams to illustrate the formation of the image of the blackboard writing by his eye lens when he is seated at the $(i)$ front desk,$(ii)$ last desk.
$(b)$ Name the defect of the eye from which the student is suffering.
$(c)$ Name the type of lens that would enable him to see the blackboard writing clearly when seated at the front desk. Draw a ray diagram to illustrate how this lens helps him to see clearly.
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