Home
Class 12
PHYSICS
The near and far points of a person are ...

The near and far points of a person are at `40 cm` and `250cm` respectively. Find the power of the lens he/she should use while reading at `25cm`. With this lens on the eye, what maximum distance is clearly visible?

Text Solution

Verified by Experts

If an object is placd at 25 cm from the correcting lensl it should produce the virtual image at 40 cm. Thus, `u=-25cm, v=-40cm`
`1/f=1/v-1/u`
`=1/(40cm)+1/(25cm)`
or `f=200/3cm=+2/3m`
`P=1/f+1.5D`
The uN/Aided eye can see a maximum distance of 250 cm. Suppose the maximum distance for clear vision is d when the lens is used. Then the object at a distance d is imaged by the lens ast 250 cm. We have
`1/v-1/u=1/f`
`or - 1/(250cm)-1/d=3/(200cm)`
`or d=-53cm`
Thus the person will be able to see up to a maximum distance of 53 cm.
Promotional Banner

Topper's Solved these Questions

  • OPTICAL INSTRUMENTS

    HC VERMA|Exercise Short Answer|11 Videos

  • OPTICAL INSTRUMENTS

    HC VERMA|Exercise Question for short Answer|1 Videos

  • OPTICAL INSTRUMENTS

    HC VERMA|Exercise Exercises|23 Videos

  • MAGNETIC PROPERTIES OF MATTER

    HC VERMA|Exercise Exercises|9 Videos

  • PERMANENT MAGNETS

    HC VERMA|Exercise Exercises|25 Videos

Similar Questions

Explore conceptually related problems

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?

The near point of a hypermetropic eye is 75 cm. What is the focal length of the lens required to see clearly an object placed at 25 cm from the eye (normal near point)?

The redius of curvature of the convex face of a plano-convex lens is 12cm and its refractive index is 1.5. a. Find the focal length of this lens. The plane surface of the lens is now silvered. b. At what distance form the lans will parallel rays incident on the convex face converge? c. Sketch the ray diagram to locate the image, when a point object is places on the axis 20cm from the lens. d. Calculate the image distance when the object is placed as in (c).

The far point of a myopic eye is 100 cm. What is the focal length of the lens required to see very distant (normal far point) objects clearly?

A far sighted person has a near point of 60"cm" . What power lens should be used for eye glasses such that the person can be read this book at a distance of 25 cm.

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 25 cm.

A point source of light is kept at a distance of 15cm from a converging lens,on its optical axis.The focal length of the lens is 10cm and its diameter is 3cm ,A screen is placed on the other side of the lens ,perpendicular to the axis of lens,at a distance 20cm from it.Then find the area of the illuminated part of the screen?

(i) If f =- 0.2 m for a glass lens, what is the power ofthe lens? (ii) The radii ofcurvature ofthe faces of a double convex lens are 15 cm and 12 cm. Its focal length is 15 cm. What is the refractive index of glass ? (iii) Refractive index and radii of curvature oftwo equal plana-convex lens are 1.5 and 20 cm respectively. They are placed in a vessel such that their convex surfaces are in contact at centre and oil ofrefractive index 1.7 is filled in them, then what will be the focal length of combination ?

In the figure shown L is converging lens of focal length 10 cm and M is a concave mirror of radius of curvature 20 cm . A point object O is placed in front of the lens at a distance 15 cm . AB and CD are optical axes of the lens mirror respectively. Find the coordinates of the final image formed by this system taking O as origin. The distance between CD & AB is 1mm.