Question

two lence have power of
(a) +2D (b) -4D
what is the Nature and focal length of each lens ?

Answer 1

Nature:-

a) convex lens

b) concave lens

Focal lengths:-

P=1/f(in m)

a) +2=1/f

f=1/2

f=0.5 m or 50 cm

b) - 4=1/f

f=1/-4

f = -0.25m or - 25 cm

Answer 2

Hello here is your Answer!!!

Topic:- Refraction of Light!


According to the Question!

Before the answer must be Revise some specific Topic;

*Lens:- Lens is a transparent medium in which two spherical lens involved.

There are two types of lense:-

1) Concave Lens

2)Convex Lens



*Power of lens used for correcting distant vision of eyes:-

*SI unit of power of lens "Dioptre".It is also known as capital"D''.


Now, Considered on Question!

Two lens have Power Given below;

1) +2D
Using Formula to determine focal length of lens,

Power=1/Focal Length

Substitute the value of power in above Formula;

Power=1/Focal length

+2=1/f

+2f=1

f=1/2

f=0.5 metre

Here, Positive Focal Length shows that to corrections of distant vision must be used Convex Lens.


Again, Considered on second Question;

2) -4D


Using Formula to determine focal length of lens,

Power=1/Focal Length

Substitute the value of power in above Formula;

Power=1/Focal length

-4=1/f

-4f=1

f=1/-4

f=-0.25 metre


Here, Focal Length (-0.25) Negative Focal Length shows that to corrections of distant vision must be used Concave Lens.

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Thanks!!!!