Physics

Optical Instruments and Human Eye

416 Questions

Optical instruments and the human eye explore how lenses and mirrors are used to magnify and resolve images. Key topics include the magnifying power of astronomical telescopes, compound microscope configurations, and hyperfocal distance calculations. These physics concepts are vital for general science competitive exams.

Telescope magnifying powerCompound microscope lensesHyperfocal distance calculationHuman eye resolutionSpherical mirror magnification

Optical Instruments and Human Eye Questions

Multiple choice structure of human eye human eye and colourful world

A person cannot see object clearly that are closed that $2m$ and father than $4m$ . To correct the eye vision the person will use :

  1. Bifocal lenses of power $0.5D$ and $0.25D$
  2. Bifocal lenses of power $0.25 D$ and $3.5D$
  3. Bifocal lenses of power $0.5 D$ and $4.0 D$
  4. Bifocal lenses of power $4.0 D$ and $0.5 D$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given,

The distance of the far point $(D) = 2m$
Let f be the focal length of the eye lens.
Image distance ( distance between eye lens and retina ) for our human eye is always constant and is about 
 $0.25m.$
This is due to the action of ciliary muscles. 
applying lens formula, we get 
$f = -D = -2 m.$
But, the power of a lens is reciprocal of focal length.
Hence. Power $=\dfrac{1}{f}.$ ( f in meters )
$\dfrac{1}{-2}=0.5$D
Similarly,
The distance of the far point $(D) = 4m$
Let f be the focal length of the eye lens.
Image distance ( distance between eye lens and retina ) for our human eye is always constant and is about 
 $0.25m.$
This is due to the action of ciliary muscles.
applying lens formula, we get 
$f = -D = -4 m.$
But, the power of a lens is reciprocal of focal length.
Hence. Power $=\dfrac{1}{f}.$ ( f in meters )
$\dfrac{1}{-4}=0.25$D
So he has to use by focal lenses

Multiple choice structure of human eye human eye and colourful world

Minimum and maximum distance should be for clear vision of healthy eye.

  1. 100 cm & 500 cm

  2. Infinite & 25 cm

  3. 25 cm & 100 cm

  4. 25 cm & infinite
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Minimum distance for clear vision of healthy eye is  $25 \ cm$ and maximum distance is infinite.

Multiple choice structure of human eye human eye and colourful world

Diameter of a human eye lens is 2 millimetre. What will be the minimum distance between two points to resolve, which are situated at the distance of 50 m from the eye? The wavelength of light is 5000 angstrom.

  1. 2.32 m

  2. 4.28 mm

  3. 1.25 cm

  4. 12.48 cm
Reveal answer Fill a bubble to check yourself
B Correct answer
Multiple choice structure of human eye human eye and colourful world

A person cannot see the object beyond 200cm. The power of lens  correct the vision will be :

  1. +0.5 D

  2. +5D

  3. -0.5D

  4. -5D
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Here, $u = \infty$ and $ v = -200\; cm$


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

$\Rightarrow \dfrac{1}{f} =- \dfrac{1}{200} + 0$

$\Rightarrow f =-2m$
$\Rightarrow  P (in \; D)= \dfrac{1}{f(in\; m)} =- 0.5 D$

Therefore, C is correct option.

Multiple choice structure of human eye human eye and colourful world

The near point and the far point of a child are at 10 and 100 cm. If the retina is 2.0 cm behind the eyelens  .What is the range of the power of the eye lens?

  1. $50 D \text { to } 40 \mathrm { D }$
  2. $60 D \text { to } 51 \mathrm { D }$
  3. $60 D \text { to } 54 \mathrm { D }$
  4. $40 D \text { to } 50 \mathrm { D }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

\begin{array}{l} According\, \, to\, question................... \ Near\, point\, of\, the\, child\, (u)=10cm \ Far\, point\, of\, the\, child\, (u)=100cm \ and,the\, \, retina\, is\, \, \, 2\, cm\, behind\, the\, eye\, lens. \ \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, V=2\, cm=0.02\, m \ Now, \ \frac { 1 }{ f } =\frac { 1 }{ { 0.02 } } -\frac { 1 }{ { (-0.1) } } \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \left| { from\, lens\, formula:\frac { 1 }{ v } -\frac { 1 }{ u } =\frac { 1 }{ f }  } \right.  \ \, \, \, \, \, \, \, \Rightarrow 50+10=60\, m \ \therefore \, \, Power\, \, of\, the\, lens:\, \, P=\frac { 1 }{ f } =60\, D \ Now,\, \, \, consider\, the\, far\, point\, is\, \, 100\, cm. \ where, \ \, u=-100cm=-1m,\, \, \, and\, \, \, \, V=2\, cm=0.02\, m \ then, \ \frac { 1 }{ f } =\frac { 1 }{ { 0.02 } } -\frac { 1 }{ { (-1) } } \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \, \left[ { we\, have\, the\, lens\, formla: } \right. \frac { 1 }{ v } -\frac { 1 }{ u } =\frac { 1 }{ f }  \ \frac { 1 }{ f } =50+1=51\, m \ \therefore \, \, \, Power\, \, of\, the\, lens:\, \, P=\frac { 1 }{ f } =51\, D \ so,\, that\, the\, rangeof\, the\, \, power\, of\, eye\, lens\, is\, from\, \, \, \underline { 60\, D\, \, to\, \, 51\, D }  \ and\, the\, correct\, option\, is\, B. \ \, \,  \ so\, the\, correct\, optuon\, is\, A. \end{array}

Multiple choice structure of human eye human eye and colourful world

A person cannot see objects clearly beyond 50cm. The power of lens to correct the vision is

  1. +5D

  2. -2D

  3. -0.5D

  4. +2D
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A person cannot see beyond 50 cm. Hence, he should use a concave lens of 50 cm focal length.Hence $Power=\dfrac{-100}{50} =-2 D$

Multiple choice structure of human eye human eye and colourful world

Long-sighted people who have lost their spectacles can still read a book by looking through a small (3-4 mm) hole in a sheet of paper :

  1. Because the fine hole produces an image of the letters at a longer distance

  2. Because in doing so the distance of the object is increased

  3. Because in doing so the focal length of the eye lens is effectively decreased

  4. Because in doing so the focal length of the eye lens is effectively increased
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Long-sighted people who have lost there spectacles can still read a book by looking through a small (3-4 mm) hole in a sheet of paper because by doing so due to the diffraction at the hole the focal length of the eye lens is effectively decreased. Hence correct option is C.

Multiple choice structure of human eye human eye and colourful world

The power of a lens used to remove the myopic defect of an eye is 0.66 D. The far point for this eye is (nearly) :

  1. 25 cm

  2. 150 cm

  3. 100 cm

  4. 75 cm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

As $p= \dfrac{1}{f}$


So, $f= \dfrac{1}{p}$

$\Longrightarrow$  $f= \dfrac{100}{0.66}cm$

$\Longrightarrow$ $f= 151.51cm$

$\Longrightarrow$ $f\simeq 150cm$

Multiple choice structure of human eye human eye and colourful world

A myopic person can not see objects lying beyond 2m. The focal length and power of the lens required to remove this defect will be 

  1. 1m and 0.5D

  2. -2m and -0.5D

  3. 0.5m and 0.5D

  4. -0.5, and 0.5D
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$u=+2m$

$v= \infty $

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

$\dfrac{1}{\infty }-\dfrac{1}{2}=\dfrac{1}{f}$

$f= -2m$

$P= \dfrac{1}{f}$

$= \dfrac{1}{-2}$

$= -0.5 D$

Multiple choice structure of human eye human eye and colourful world

A person can see clearly objects lying between 25 cm and 2 m from his eye. His vision can be corrected by using spectacles of power:

  1. +0.25 D

  2. +0.5 D

  3. -0.25 D

  4. -0.5 D
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Here, $u= 2m$
$v= \infty $

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

$\dfrac{1}{\infty}-\dfrac{1}{2}= \dfrac{1}{f}$

           $f= -2m$

Now, $P= \dfrac{1}{f}$

              $= \dfrac{1}{-2}D$

              $= -0.5\ D$

Multiple choice structure of human eye human eye and colourful world

The power of lens, a short sighted person uses is 2 dioptre. The maximum distance of an object which he can see without spectacles is 

  1. 25cm

  2. 50cm

  3. 100cm

  4. 10cm
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$f= \dfrac{1}{p}$

$= \dfrac{100}{2}cm$

$= 50\ cm$

So he can see upto a distance of 50 cm.

Multiple choice structure of human eye human eye and colourful world

A person wears glasses of power 2D. The defect of the eye and the far point of the person without the glasses will be 

  1. Nearsighted, 50 cm

  2. Farsighted, 50cm

  3. Nearsighted, 250 cm

  4. Astigmatism, 50 m
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$f= \dfrac{1}{p}$

  $=\dfrac{100}{2}cm$

  $=50\ cm$

The defect of eye will be farsighted.

Multiple choice structure of human eye human eye and colourful world

The far point of a myopic eye is 250 cm. The correcting lens should be a

  1. diverging lens of focal length 250 cm

  2. converging lens of focal length 250 cm

  3. diverging lens of focal length 125 cm

  4. converging lens of focal length 125 cm
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$u = -\infty $ 

$ v = -250 cm$

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

$(-\dfrac{1}{\infty}-\dfrac{1}{250})= \dfrac{1}{f}$

$f= -250cm$

The correcting lens of focal length $250 cm$.

Multiple choice structure of human eye human eye and colourful world

The power of accommodation for the normal eye is

  1. 4 D

  2. 40 D

  3. 44 D

  4. 400 D
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Our normal vision length = 25 cm which is eye lens focal length focal length  $f = 0.25 m$

Power $P=\dfrac{1}{f}=\dfrac{1}{.25}=4D$