Physics

Optics and Lenses

251 Questions

Enhance your physics knowledge by practicing questions on optics and the functioning of lenses. The set covers calculating combined focal lengths, lens power, and correcting vision defects like myopia and hypermetropia. These physics fundamentals are crucial for medical entrance and state board exams.

Combined focal lengthCorrecting vision defectsLens power calculationConvex and concave lensesTelescopesHuygens principle

Optics and Lenses Questions

Multiple choice structure of human eye human eye and colourful world

A man cannot see clearly the objects beyond a distance of 20 cm from his eyes. To see distant objects clearly the kind of lenses and its focal length must be 

  1. 100 cm convex

  2. 100 cm concave

  3. 20 cm convex

  4. 20 cm concave
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$u= +20cm$

$v= \infty $

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

$\dfrac{1}{\infty }-\dfrac{1}{+20}= \dfrac{1}{f}$

$f=-20\ cm$

Multiple choice structure of human eye human eye and colourful world

A long sighted person has a least distance of distinct vision of 50 cm. He wants to reduce it to 25 cm. He should use a :

  1. Concave lens of focal length 50 cm

  2. Convex of focal length 25 cm

  3. Convex lens of focal length 50 cm

  4. Concave lens of focal length 25 cm
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given, $u= \infty $


Image distance, $v= 50cm$

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

$\dfrac{1}{50}-\dfrac{1}{\infty }= \dfrac{1}{f}$

$f= +50\ cm$

He should use a convex lens of focal length 50 cm.

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

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 person can see clearly between 1 m and 2 m his corrective lenses should be 

  1. Bifocals with power -0.5 D and additional +3.5 D

  2. bifocals with power -1.0 D and additional +3 D

  3. Concave with power 1.0 D

  4. convex with power 0.5 D
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

To see at 1 m (near point correction), the lens needs P = 1/0.25 - 1/1 = 3D. To see at infinity (far point correction), the lens needs P = 1/infinity - 1/2 = -0.5D. Bifocals are needed.

Multiple choice structure of human eye human eye and colourful world

Which of the following lenses of appropriate focal length is used to correct shortsightedness ?

  1. Concave

  2. Convex

  3. Both A & B

  4. None of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A convex lens of appropriate focal length is used to correct farsightedness.
Farsightedness is the inability to see nearby objects clearly due to the formation of image by convergence of rays at a point behind the retina. A convex or converging lens with the correct focal length allows the rays to converge at a point on the retina. The convex lens first converge the rays before it reaches the eye and thus, reducing the image distance. The eye-lens will now be able to converge the refracted rays ton the retina.

Multiple choice evs reflection of light by plane surfaces characteristics of an image formed by a plane mirror formation of image in a plane mirror characteristics of the image formed by a plane mirror

If $x _1$ be the size of the magnified image and $x _2$ the size of the diminished image in Lens Displacement Method, then the size of the object is

  1. $\sqrt{x _1x _2}$
  2. $x _1x _2$
  3. $x _1^2x _2$
  4. $x _1x^2 _2$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The size of the object in accordance with the Fresnel's displacement law is given by $\sqrt{x _1x _2}$.

Multiple choice evs we are special defects of eye disorders of nervous system braille script

Concave lens is used to correct 

  1. Myopia

  2. Presbiopia

  3. Hypermetropia

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

Myopia is nearsightedness and short-sightedness, is a condition of the eye where the light that comes in does not directly focus on the retina but in front of it, causing the image that one sees when looking at a distant object to be out of focus, but in focus when looking at a close object.
It can be corrected by the use of corrective lenses that have a negative optical power i.e., concave glasses which compensates for the excessive positive diopters of the myopic eye.
So, the correct answer is option A.

Multiple choice evs we are special defects of eye disorders of nervous system braille script

Concave lens is employed to correct _______.

  1. Presbyopia

  2. Hypermetropia

  3. Cataract

  4. Myopia
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
A. Presbyopia occurs in the late age (generally after 40 years) due to loss of elasticity of eye lens due to which nearby objects are not correctly visible. It is corrected by using bifocal lengths.
B. Hypermetropia occurs when eye ball becomes shorter and it results in the formation of image behind the retina. It is corrected using convex lens which focus the light rays on the retina.
C. Cataract is an eye disease that occurs in older people. The visibility is reduced because the eye lens becomes opaque. It is treated by surgery.
D. Myopia occurs when eye ball becomes longer and it results in the formation of image in front of retina. It is corrected using concave lens which diverge the light rays to get focussed on the retina. 
So, the correct answer is 'Myopia'.
Multiple choice evs we are special defects of eye disorders of nervous system braille script

Convex lenses correct

  1. Presbyopia

  2. Myopia

  3. Hypermetropia

  4. Glaucoma
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
A. Presbyopia occurs in the late age (generally after 40 years) due to loss of elasticity of eye lens due to which nearby objects are not correctly visible. It is corrected by using bifocal lengths.
B. Myopia occurs when eye ball becomes longer and it results in the formation of image in front of retina. It is corrected using concave lens which diverge the light rays to get focussed on the retina. 
C. Hypermetropia occurs when eye ball becomes shorter and it results in the formation of image behind the retina. It is corrected using convex lens which focus the light rays on the retina.
D. Glaucoma is a disorder of eye in which the optic nerve which carries visual information to brain, is damaged and this leads to blindness.
So, the correct answer is 'Hypermetropia'.
Multiple choice evs we are special defects of eye disorders of nervous system braille script

Convex lens is used to correct 

  1. Hypermetropia

  2. Myopia

  3. Cataract

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

Hypermetropia occurs when the light is focused behind the retina. So, the lens changes its thickness, which aims to bring the light into focus on the retina - a process is called as accommodation. But, people with long sight cannot accommodate fully and so the light does not focus sharply and vision is blurred. This occurs because either the eyeball is too short, the cornea is too flat or the lens cannot become round enough. The simplest, cheapest and safest way to correct long-sightedness is with glasses. 

Convex prescription lenses (called as plus lenses) are used to bend light rays slightly inwards. The light rays then have a lesser angle to bend back to focus, when travelling through the cornea and lens. As a result, the light rays focus further forward on the retina. 

Multiple choice evs we are special defects of eye disorders of nervous system braille script

To correct myopia, one should use 

  1. Convex lens

  2. Concave lens

  3. Plane lens

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Myopia also known as nearsightedness or short-sightedness is a condition of the eye where light focuses in front, instead of on the retina. People having myopia can see close objects clearly, but objects farther away appear blurred. It occurs if the eyeball is too long or the cornea is too curved. So, the correct answer is option B.

Multiple choice botany cell and cellular organization cell theory microscope cell and its discovery

Lenses used in ultraviolet microscope are

  1. Glass lenses.

  2. Quartz fluorite.

  3. Lithium fluoride.

  4. Both B and C.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Standard glass lenses absorb ultraviolet light, making them unsuitable for UV microscopy. Quartz and fluorite are transparent to UV radiation, so lenses made from these materials are used instead.

Multiple choice

Type of lens to correct for myopia

  1. Diverging

  2. Convex

  3. Converging

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

Myopia (nearsightedness) is corrected with a diverging (concave) lens, which spreads out the light rays before they reach the eye to compensate for the eye's tendency to focus light too far in front of the retina.