Tag: human eye and colourful world

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Questions Related to human eye and colourful world

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.

Multiple choice structure of human eye human eye and colourful world

A person suffering from eyesight defect has far point at $40cm$ and near point at $25cm$. The person uses a lens to see far away object. Find the near point of the person while wearing this lens.

  1. $50cm$
  2. $\dfrac{200}{13}cm$
  3. $\dfrac{200}{3}cm$
  4. $25cm$
Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice structure of human eye human eye and colourful world

A farsighted woman breaks her current eyeglasses and is using an old pair whose refractive power is 1.660 diopters. Since these eyeglasses do not completely correct her vision, she must hold a newspaper 42.00 cm from her eyes in order to read it. She wears the eyeglasses 2.00 cm from her eyes. How far is her near point from her eyes?

  1. 75 cm

  2. 125 cm

  3. 225 cm

  4. 121.05 cm
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The refractive power of the lens is $1.660$ dipters. So the focal length of the lens is $f=\dfrac{1}{1.660}=0.6024\,m=60.24\,cm$

The distance between the newpaper and her eyes is $42.00\,cm$

The distance between her eyes and glasses is $2.00\,cm$

So, the distance between the lglasses and newspaper is $(42.00-2.00)\,cm=40.00\,cm.$ That is, $d _0=40.00\,cm$

The distance $(d _i)$ between the glasses and the virtual image formed by the lens given by,

$d _i=\dfrac{fd _0}{d _0-f}=\dfrac{60.24-40.00}{40.00-60.24}=-119.05\,cm$

This relation is obtained from thin lens equation and the negative sign implies the image is virtual.

This position is her near point.

So the near point from her eyes is, $119.05\,cm+2.00\,cm=121.05\,cm$
Multiple choice structure of human eye human eye and colourful world

Myopia can be corrected by using spectacle having ________.

  1. Concave lens

  2. Convex lens

  3. Biconvex lens

  4. Biconcave lens
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Myopia (nearsightedness) occurs when light focuses in front of the retina. A concave lens is used to diverge the light before it enters the eye, pushing the focal point back onto the retina.

Multiple choice structure of human eye human eye and colourful world

A girl whose eyes are $150  \mathrm{cm}  $ above the ground looks at her reflection in a vertical mirror $ 250  \mathrm{cm}  $ away. The top and bottom of the mirror are $200 \mathrm{cm}  $ and  $120 \mathrm{cm} $ above the ground respectively. What length below her eyes can she see of herself in the mirror?

  1. $60 cm$
  2. $75 cm$
  3. $100 cm$
  4. $120 cm$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The girl's eyes are at 150 cm. The mirror spans 120 cm to 200 cm. The portion of the mirror she can see is determined by the geometry of reflection. She can see the part of the mirror from 120 cm to 200 cm, which is 80 cm, but the question asks for the length of herself she can see, which is twice the mirror height available relative to her eye level.

Multiple choice structure of human eye human eye and colourful world

A student of class $  10,  $ is not able to see clearly the black board question when seated at a distance of $5  \mathrm{m}  $ from the board,the defect he is suffering from is

  1. Myopia

  2. Hypermetropia

  3. Presbyopia

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

If a student cannot see distant objects (like a blackboard) clearly, they are suffering from myopia (nearsightedness).

Multiple choice structure of human eye human eye and colourful world

A man can see clearly up to $3\ \textit{metres}$. Prescribe a lens for his spectacles so that he can see clearly up to $12\ \textit{metres}$

  1. $-3/4\ D$
  2. $3\ D$
  3. $-1/4\ D$
  4. $-4\ D$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The lens must form an image at 3 m for an object at 12 m. 1/f = 1/v - 1/u = 1/-3 - 1/-12 = -4/12 + 1/12 = -3/12 = -1/4. Power P = 1/f = -0.25 D.

Multiple choice structure of human eye human eye and colourful world

Myopia is a defect of vision caused by

  1. decrease in the retinal distance from the lens

  2. a decrease in the diameter of the eyeball

  3. an increase in the thickness of the lens

  4. an increase in the curvature of the lens
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Myopia is primarily caused by an elongated eyeball or an increase in the curvature of the lens, both of which cause light to converge in front of the retina instead of on it.

Multiple choice structure of human eye human eye and colourful world

A professor reads a greeting card on his 50th birthday with +2.5D glasses keeping the card 25 cm away. 10 years later he reads the greeting card  with same glasses keeping the card 50 cm away.What power should he wear now?

  1. 2D

  2. 0.5D

  3. 2.25D

  4. 4.5D
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$ \dfrac { 1 }{ { f }^{ ' } } =\dfrac { 1 }{ 25 } -\dfrac { 1 }{ 50 } =\dfrac { 1 }{ 50 } \quad or$


$ P=2D$

${ p } _{ net }=2.5+2=4.5D$

Multiple choice structure of human eye human eye and colourful world

A person cannot see distinctly at the distance less than one metre. Calculate the power of the lens that he should use to read a book at a distance of $25\, cm$

  1. $+ 3.0\, D$
  2. $+ 0.125\, D$
  3. $- 3.0\, D$
  4. $+ 4.0\, D$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The person needs to see an object at 25 cm (u = -0.25 m) as if it were at 1 m (v = -1 m). 1/f = 1/v - 1/u = 1/-1 - 1/-0.25 = -1 + 4 = 3. Power P = +3.0 D.