Question

plz help me

A person can see clearly up to 3.0 m. describe the type of lens that should be used so that he can see upto 12 m clearly .

Answer 1

Answers :-

distance of object (u) = – 12 m
distance of the image (v) = –3m

we calculate ,

I) focal length (f) =?
ii) power of the lens (p) = ?

I) 1/v – 1/u = 1/f

1/–3 – (–1/12) = 1/f

1/f = –4+1/ 12

1/f = –3/12

1/f = –1/4

so,

f = –4.0

we know that ,

Negative sign indicate that the lens used should be concave

ii) power = 1/f (in metre )

p = 1/–40

P = – 0.25 dioptre


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Answer 2

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