Tag: structure of human eye

Questions Related to structure of human eye

A person suffering from myopia cannot see beyond 1m. What should be the focal length of the concave lens that will correct his vision?

structure of human eye human eye and colourful world

  1. -1 m

  2. -2 m

  3. 0.5 m

  4. 10 m

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Correct Option: A
Explanation:

The focal length of the concave lens should be -1 m as object at infinity forms image at focus.

Astigmatism occurs when the cornea does not have a truly spherical shape. This defect can be cured by the use of a :

structure of human eye human eye and colourful world

  1. concave lens

  2. cylindrical lens

  3. convex lens

  4. plano-convex lens

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Correct Option: C
Explanation:

Astigmatism occurs when the cornea does not have a truly spherical shape. This defect can be cured by the use of a convex lens.

The near point of a person is $75cm$. In order that he may be able to read book at a distance $25cm$. The power of spectacles lenses should be

structure of human eye human eye and colourful world

  1. $-2D$

  2. $+3.75D$

  3. $+2.6D$

  4. $+3D$

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Correct Option: C

An old person is able to see an object nearest to 1 m.What should be the power of lens required so that he can see an object placed at nearest distance of distinct vision?

structure of human eye human eye and colourful world

  1. 3D

  2. 4D

  3. 1/2D

  4. 1/4D

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Correct Option: A
Explanation:

Hypermetropia is a condition of the eye where the person is not able to see things clearly when nearer to the eye.

The normal near point of the eye is \[u=25\text{ }cm\]

Focal length, $f$

Image formed at distance, $v=100\,cm$

$ \dfrac{1}{f}=\dfrac{1}{v}-\dfrac{1}{u} $

$ \dfrac{1}{f}=\dfrac{1}{25}-\dfrac{1}{100}=\dfrac{3}{100} $

$ f=33.33\,cm=0.33\,m $

Power, $P=\dfrac{1}{f}=\,\dfrac{1}{0.333}=3D$

Hence, Power of lens is $3D$

A far-sighted person cannot focus distinctly objects closer than 120 cm. The lens that will permit him to read from a distance of 40 cm will have a focal length:

structure of human eye human eye and colourful world
    • 30 cm
    • 30 cm
    • 60 cm
    • 60 cm
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Correct Option: C
Explanation:

Given,

Near point, $v=-120\,cm$

Reading Distance, $u=-40\,cm$

From lens formula,

  $ \dfrac{1}{f}=\dfrac{1}{v}-\dfrac{1}{u}=\dfrac{1}{-120}-\dfrac{1}{-40}=\dfrac{1}{60} $

 $ f=+60\,cm $

Focal length of lens $f=+60\,cm$ 

Which part of eye can change the curvature of eye-lens and make it thin or thick according to the need of eye?

structure of human eye human eye and colourful world

  1. Iris

  2. Pupil

  3. Cornea

  4. Ciliary muscles

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Correct Option: A

For a normal eye, The cornea of eye provides a converging power of $40 \,D$ and the least converging power of the eye lens behind the cornea is $20 \,D$. Using this information, the distance between the retina and the cornea eye lens can be estimated to be.

structure of human eye human eye and colourful world

  1. $1.5 \,cm$

  2. $5 \,cm$

  3. $2.5 \,cm$

  4. $1.67 \,cm$

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Correct Option: D
Explanation:
Power of Cornea, $P _1=40 D$
and power of the eye lens,  $P _2 =20D$
${ P } _{ eff }= P _1+P2$
$\Rightarrow P _{eff}=40D+20D=60D$
So, $f=\dfrac{100}{P _{ eff }}=\dfrac{100}{60}=1.67cm$
Hence, the correct option is $(D)$

Which of the following is true for a person suffering from myopia?

structure of human eye human eye and colourful world

  1. Can see far-off object clearly but near objects appear blurred

  2. can be corrected using a convex lens

  3. far point is at finite distance, and not at infinity

  4. near point is beyond 25 cm

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Correct Option: C

A person can see clearly objects only when they lie between $50$cm and $400$cm from his eyes. In order to increase the maximum distance of distinct vision to infinity, the type and power of the correcting lens, the person has to use, will be?

structure of human eye human eye and colourful world

  1. Convex, $+2.25$ dioptre

  2. Concave, $-0.25$ dioptre

  3. Concave, $-0.2$ dioptre

  4. Convex, $+0.15$ dioptre

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Correct Option: B
Explanation:

Maximum distance of distinct vision $=400$cm. So image of object at infinity is to be formed at $400$cm


Use lens formula, $\dfrac{1}{v}-\dfrac{1}{u}=\dfrac{1}{f}$

$\dfrac{1}{-400}-\dfrac{1}{\infty}=\dfrac{1}{f}$

$P=-0.25$D.

A far sighted person can see object beyond $71\;cm$ clearly if the separation between the glasses and eye lens is $2\;cm$, then find the focal length of glasses.

structure of human eye human eye and colourful world

  1. $23\;cm$

  2. $34.5\;cm$

  3. $18.4\;cm$

  4. $30\;cm$

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Correct Option: C