Question

Ashok from standard 9th uses spectacles. The power of the lenses in his spectacle is -0.5 diopter .
Answer the following:
(a)state the type of lens is used in spectacles.
(b)Name the defect of vision Ashok is suffering from.
(c) Find the focal length of the lens is used in his spectacles.

Answer 1

a) Concave lens is used in his spectacles.
b) Ashok is suffering from myopia.
c) W.K.T P=1/f
f=1/P
f=1/-0.5D
f=10/-5
f=-2m or -200cm

Answer 2

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a) The type of the lenses used in his spectacles is

concave lens as the power of the lens is negative.

b) The defect of vision Aniket suffering from is myopia (nearsightedness).

c) Given : Power of a concave lens ⟶ - 0.5 D

To find : The focal length of the lens (f)

Solution :

We know that,

P = 1 / f (m)

0.5 = 1 / f

∴ f = 1 / 0.5

∴ f = 10 / 5

∴ f = 2 m

Hope it helps!

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