Home
Class 12
PHYSICS
A person who can see objects clearly at ...

A person who can see objects clearly at a distance of 10cm , requires spectacles to be able to see clearly objects at a distance of 30 cm. what type of spectacle should he use? Find the focal length of the lens.

Text Solution

Verified by Experts

The image of an object at a distance of 30 cm has to be formed at a distance of 10 cm . In this case , u=-30 cm , v=-10 cm . If the focal length of the lens used is f then ,
`1/f=1/v-1/u=1/(-10)-1/(-30)=1/(30)-1/(10)=(1-3)/(30)=-1/(15) or, f=-15 cm `
Since f is negative , the person should use a spectacle with a concave lens.
Promotional Banner

Topper's Solved these Questions

  • OPTICAL INSTRUMENTS

    CHHAYA PUBLICATION|Exercise CBSE SCANNER|8 Videos

  • OPTICAL INSTRUMENTS

    CHHAYA PUBLICATION|Exercise ENTRANCE CORNER ( Integer answer type )|2 Videos

  • Magnetic Properties of Materials

    CHHAYA PUBLICATION|Exercise CBSE SCANNER|11 Videos

  • QUANTUM THEORY

    CHHAYA PUBLICATION|Exercise CBSE Scanner|29 Videos

Similar Questions

Explore conceptually related problems

A Person who can see objects clearly at a distance of 10cm, required spectacles to be able ot see clearly objects at a distance of 30cm. What types of spectacle should he use? Find the focal length of the lens.

A person who can see things most clearly at a distance of 10 cm , requires spectacles to be able to see clearly things at a distance of 30 cm . What should be the focal length of the spectacles ?

A shortsighted man can read the writings of a book keeping it at a distance of 15 cm from his eyes. To read the book placed at a distance of 60 cm from his eyes what type of spectacles should he use ? What will be the power of the spectacles ?

A person can see distinctly up to a distance of 2 m and no further. To see distinctly up to a long distance what type of spectacles should he use? What will be the power of the lens of the spectacles?

A short sighted person can see objects at 20cm from his eyes. What type of lens is to be used to see clearly objects at 100cm away?

Normal eye cannot see the object nearby from a distance of 25 cm , as

A short-sighted person can see distinctly the object situated at a distance of 20 cm from him. What type of lens will he use to see the objects situated at a distance of 100 cm from him ? What will be the power of the lens ?

A short-sighted person can read a book only up to 15 cm from his eyes. To read a book placed at a distance of 25 cm from him what type of spectacles should he use? What be the power of the spectacles?

A person with defective eyes can see the objects distinctly up to the distance 20 cm . What type of lens should be used and of what power?