Advertisements
Advertisements
Question
The near point of the eye of a person is 50 cm. Find the nature and power of the corrective lens required by the person to enable him to see clearly the objects placed at 25 cm from the eye?
Advertisements
Solution
Given:
Object distance (u) = −25cm
Image distance (v) = −50cm
Focal length, f = ?
Using the lens formula
`1/"f" = 1/"v" - 1/"u"`
`1/"f" = 1/(-50) - 1/(-25)`
`1/"f" = -1/50 + 1/25`
`1/"f" = (-1+2)/50`
`1/"f" = 1/50`
`"f"` = 50 cm
Since the focal length of the lens is positive, the corrective lens required is a convex lens.
`"f"` = 50cm
`"f"` = 0.5m
Power (P) of the corrective lens will be
`"P" = 1/("f"("m"))`
`"P" = 1/0.5`
`"P" = + 2 "D"`
APPEARS IN
RELATED QUESTIONS
Name any two defects of vision which can be corrected by using spectacles.
Name the following:
The eye defect caused due to shortening of the eye ball from front to back.
Describe the mechanism of focusing the image of a distant object in your eye when you raise your head after reading a book.
Enumerate the common defects of vision, their causes and the possible methods of correcting them.
Choose the odd one out from the following terms and name the category to which the others belong.
Endolymph, Tympanic membrane, Semi-circular canal, Blind spot
Give Reason:
Deficiency of vitamin A causes night blindness.
Explain the Term: Presbyopia
Explain the Term: Astigmatism
A teacher drew the diagram of the heart on the blackboard and told the students to copy it in their notebooks. Mahesh couldn't see the diagram clearly as it appeared blurred to him.
- Name the defect of the eye Mahesh is suffering from.
- Where is the image formed in this defect?
- Mahesh consults an eye doctor and is prescribed suitable lenses to correct the defect. Which type of lens do his spectacles have?
Given alongside is a diagram depicting a defect of the human eye. Study the same and answer the questions that follow:
 |
- Name the defect shown in the diagram.
- Give two possible reasons for this defect.
- Name the parts labelled 1 to 4.
- Name the type of lens used to correct this eye defect.
- Draw a labelled diagram to show how the above mentioned defect is rectified using the lens named above.
