When is a person said to have developed cataract in his eye? How is the vision of a person having cataract restored?
Cataract develops when the eye-lens of a person becomes unclear due to the formation of a membrane over it. The vision of a person having cataract can be restored after getting cataract surgery done on the eye-lens having cataract. This defect cannot be corrected by any type of spectacle lenses.
Why does the objective lens of an astronomical telescope have a large light gathering power?
Give the condition required to achieve a larger magnification of a small object by a compound microscope ?
A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?
Where should an object be placed in front of a convex lens so as to use it as a simple microscope?
Which of the two, objective or eye-piece, of a telescope has a large aperture? Give reason for your answer.
A person having a myopic eye used the concave lens of focal length 50cm. What is the power of the lens?
If we need magnification of 375 from a microscope of tube length 15 cm and objective of focal length 0.5 cm, what focal length of eye-piece should we use?
A person uses convex lens spectacles. What vision defect does he have? Draw a diagram
(i) to show the defective eye
(ii) to show the correction with the lens.
A person needs a lens of power – 4.5 D for correction of her vision.
(a) What kind of defect in vision is she suffering from?
(b) What is the focal length of the corrective lens?
(c) What is the nature of the corrective lens?
A person needs a lens of power −5.5 dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?
A 52-year old near-sighted person wears eye-glass with a power of –5.5 dioptres for distance viewing. His doctor prescribes a correction of +1.5 dioptres in the near-vision section of his bi-focals. This is measured relative to the main part of the lens (i) What is the focal length of his distance-viewing part of the lens? (ii) What is the focal length of the near-vision section of the lens?
A student has difficulty reading the blackboard while sitting in the last row. What could be the defect the child is suffering from ? How can it be corrected ?
Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye ¡s 1 m. What ¡s the power of a lens required to correct this defect? Assume that near point of the normal eye is 25 cm.
When is a person said to have developed cataract in his eye? How is the vision of a person having cataract restored?
A compound microscope has an objective of focal length 1.0 cm and an eyepiece of focal length 4.0 cm. If the length of the tube is 20 cm, find the magnification of the compound microscope.
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?
Which phenomenon of vision is made use of in cinematography? Explain briefly how it is used.