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

15 cm (Concave)

15 cm (convex)

10 cm

0

Solution

15 cm (Concave)

A concave lens is required by the person so that the lens forms the image of object distant 30 cm, at 10 cm it means.

$u = - 30 cm, ν = - 10 cm \frac{1}{f} = \frac{1}{ν} - \frac{1}{u} = \frac{1}{- 10} - \frac{1}{- 30} = - \frac{2}{30} or \frac{1}{f} = \frac{- 1}{15} Minus sign signifies that lens used is concave .$

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Ray Optics And Optical Instruments

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

15 cm (Concave)

15 cm (convex)

10 cm

0

Some More Questions From Ray Optics and Optical Instruments Chapter

Show using a proper diagram how unpolarised light can be linearly polarised by reflection from a transparent glass surface.

Draw a ray diagram to show image formation when the concave mirror produces a real, inverted and magnified image of the object.

Explain two advantages of a reflecting telescope over a refracting telescope.

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For Daily Free Study Material Join wiredfaculty

Ray Optics And Optical Instruments

A person who can see things most clearly at a distance of 10 cm, requires spectacles to enable to see clearly things at a distance of 30 cm. What should be the focal length of the spectacles? 15 cm (Concave) 15 cm (convex) 10 cm 0

Some More Questions From Ray Optics and Optical Instruments Chapter

Show using a proper diagram how unpolarised light can be linearly polarised by reflection from a transparent glass surface.

Draw a ray diagram to show image formation when the concave mirror produces a real, inverted and magnified image of the object.

Explain two advantages of a reflecting telescope over a refracting telescope.

An experiment is performed to find the refractive index of glass using a travelling microscope. In this experiment distance are measured by

Two lenses of power -15D and +5D are in contact with each other. The focal length of the combination is

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

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

15 cm (Concave)

15 cm (convex)

10 cm

0