Which one among the following statements related to human eye is correct?
- A.For a person suffering from short-sight defect, the image of a distant object is focused behind the retina.
- B.Short-sight defect can be corrected by a converging spectacle lens.
- C.For a person suffering from long-sight defect, the image of a near object is focused behind the retina.
- D.Long-sight defect can be corrected by a diverging spectacle lens.
Correct answer
Explanation
The correct answer is C. In long-sightedness (hypermetropia) the eye cannot see nearby objects clearly because their image is formed behind the retina.
Hypermetropia happens when the eyeball is too short or the eye lens is not converging enough, so light from a close object has not yet come to a focus when it reaches the retina. A convex, converging lens in front of the eye adds the missing power and brings the image onto the retina. In short-sightedness (myopia) the opposite occurs: the eyeball is too long or the lens too strong, so a distant object's image forms in front of the retina, and a concave, diverging lens corrects it.
A is wrong because in short-sight the image of a distant object falls in front of the retina, not behind it. B is wrong because short-sight needs a diverging, concave lens. D is wrong because long-sight needs a converging, convex lens.
Exam tip: myopia = image in front, concave lens; hypermetropia = image behind, convex lens; presbyopia = ageing, bifocal lens.
Practice Questions
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- A.7 A
- B.5 A
- C.4 A
- D.2 A
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- C.Both 1 and 2
- D.Neither 1 nor 2
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- C.The charge of beta (β) particle is +2.
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