Tag: structure of human eye

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Questions Related to structure of human eye

Multiple choice structure of human eye human eye and colourful world

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

  1. -1 m

  2. -2 m

  3. 0.5 m

  4. 10 m
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

Multiple choice structure of human eye human eye and colourful world

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

  1. concave lens

  2. cylindrical lens

  3. convex lens

  4. plano-convex lens
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

Multiple choice structure of human eye human eye and colourful world

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

  1. $-2D$
  2. $+3.75D$
  3. $+2.6D$
  4. $+3D$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using the lens formula 1/f = 1/v - 1/u. Here, v = -75 cm and u = -25 cm. 1/f = 1/-75 - 1/-25 = -1/75 + 3/75 = 2/75. Power P = 100/f = 100 * (2/75) = 200/75 = 2.66D.

Multiple choice structure of human eye human eye and colourful world

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?

  1. 3D

  2. 4D

  3. 1/2D

  4. 1/4D
Reveal answer Fill a bubble to check yourself
A Correct answer
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 $3D$

Multiple choice structure of human eye human eye and colourful world

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:

    • 30 cm
    • 30 cm
    • 60 cm
    • 60 cm
Reveal answer Fill a bubble to check yourself
C Correct answer
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 $f=+60\,cm$ 

Multiple choice structure of human eye human eye and colourful world

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

  1. Iris

  2. Pupil

  3. Cornea

  4. Ciliary muscles
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The ciliary muscles contract and relax to alter the shape and curvature of the crystalline eye lens, allowing the eye to focus on objects at varying distances through accommodation.

Multiple choice structure of human eye human eye and colourful world

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.

  1. $1.5 \,cm$
  2. $5 \,cm$
  3. $2.5 \,cm$
  4. $1.67 \,cm$
Reveal answer Fill a bubble to check yourself
D Correct answer
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 $(D)$

Multiple choice structure of human eye human eye and colourful world

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

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In myopia, the eyeball is too long or the lens is too curved, causing light to focus in front of the retina. Consequently, the far point is brought closer than infinity, making distant objects blurry.

Multiple choice structure of human eye human eye and colourful world

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?

  1. Convex, $+2.25$ dioptre
  2. Concave, $-0.25$ dioptre
  3. Concave, $-0.2$ dioptre
  4. Convex, $+0.15$ dioptre
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

Multiple choice structure of human eye human eye and colourful world

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.

  1. $23\;cm$
  2. $34.5\;cm$
  3. $18.4\;cm$
  4. $30\;cm$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For a farsighted person, the lens must form a virtual image of an object at the near point (71 cm) at the person's actual near point. Accounting for the 2 cm separation between the lens and eye, the object distance u is infinity and image distance v is -(71 - 2) = -69 cm, or using standard lens formula with u = -71 cm and v = -(71 - 2) = -69 cm. Using the lens formula 1/f = 1/v - 1/u yields the correct focal length.