Question

the power of a lens is -3.5 D find the focal length and the type of lens

Answer 1

Answer:

convex length

f=R/2 -3.5/2=-1.75

this will be the answer

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Answer 2

Given:

The power of a lens is - 3.5 D


To Find:

The focal length and the type of lens


Solution:

We know that,


=> f = 1 / P


Here,

=> f = focal length

=> P = power


Units:

=> f = metre (m)

=> P = Dioptre (D)


According to the question,

We are asked to find the focal length and the type of lens


So, we must find “f”


Given that,

The power of a lens is - 3.5 D


Hence,

P = - 3.5 D


By substituting the value,

We get,


=> f = 1 /- 3.5 m

=> f = - 0.285 m


By approximation,

We get,


=> f = - 0.29 m


Therefore,

=> Focal length = - 0.29 m


According to the question,

We are also asked to find the type of lens


We found out that,

=> Focal length = - 0.29 m


Since,

The focal length of the lens is negative


Therefore,

The given lens is a Concave lens