Lakhmir Singh & Manjit Kaur Test: The Human Eye & the Colourful World - 1 - UPSC MCQ

The near point of the eye is the minimum distance of the object from the eye, which can be seen distinctly without strain. For a normal human eye, this distance is 25 cm.

The far point of the eye is the maximum distance to which the eye can see the objects clearly. The far point of the normal human eye is infinity.

The light ray bends towards the normal as it travels from a rarer medium of air to a denser medium of water, undergoes refraction. Refraction is due to change in speed of light  as it enters from one transparent medium to another. The speed of light increases in rarer medium and decreases in denser medium.

The human eye forms the image of an object at its Retina.
The retina is a light-sensitive layer of tissue located at the back of the eye. It contains specialized cells called photoreceptors that convert light into electrical signals. These signals are then transmitted to the brain via the optic nerve, where they are interpreted as visual images.
Explanation:
- The retina is responsible for capturing the image of an object and converting it into electrical signals.
- It is composed of multiple layers, including the outermost layer called the pigmented epithelium, which absorbs excess light and provides nourishment to the photoreceptor cells.
- The innermost layer of the retina contains the photoreceptor cells, namely rods and cones. Rods are responsible for detecting dim light and are more sensitive to motion, while cones are responsible for color vision and detailed visual acuity.
- When light enters the eye, it passes through the cornea, the transparent outer covering of the eye, and the lens, which focuses the light onto the retina.
- The lens adjusts its shape to allow for accommodation, which is the process of focusing on objects at different distances.
- The light that reaches the retina stimulates the photoreceptor cells, which then send electrical signals to the brain via the optic nerve.
- The brain processes these signals and interprets them as visual images, allowing us to perceive the world around us.
In conclusion, the retina is the part of the eye where the image of an object is formed. It plays a crucial role in the process of vision by converting light into electrical signals that the brain can interpret.

To correct a myopic (nearsighted) person's vision, a concave lens is required. Here's a detailed explanation:
Definition:
- Myopia is a refractive error in which distant objects appear blurred, while close objects can be seen clearly.
- The far point is the point at which parallel rays of light entering the eye converge to form a focused image on the retina without any additional accommodation by the eye.
Explanation:
- In a myopic person, the far point of vision is closer than the normal distance of infinity.
- In this case, the far point is given as 80 cm in front of the eye.
- To correct the problem and bring the far point back to infinity, a lens is used.
Types of lenses:
- Convex lenses are thicker in the middle and thinner at the edges. They converge light rays and are used to correct hyperopia (farsightedness).
- Concave lenses are thinner in the middle and thicker at the edges. They diverge light rays and are used to correct myopia (nearsightedness).
Correct answer:
- In this case, to correct the myopic person's vision with a far point of 80 cm, a concave lens is required. Therefore, the correct answer is option A: Concave.

When red and blue light are combined, the result is magenta. When green and blue light are combined, they make cyan. Red and green light make yellow. And when all three primary colors of light  are combined, we see white light.

C is the correct option.Refractive Index (Index of Refraction) is a value calculated from the ratio of the speed of light in a vacuum to that in a second medium of greater density. In the question the lowest refractive index is of Q (1.33), then P (1.73), and the highest is R (2.24).

Presbyopia is a condition associated with the aging of the eye that results in progressively worsening ability to focus clearly on close objects.

Light waves are electromagnetic waves:

• Light waves are a type of electromagnetic waves.


• Electromagnetic waves are waves that consist of both electric and magnetic fields oscillating perpendicular to each other and to the direction of wave propagation.


• Light waves are a form of electromagnetic radiation that can be detected by the human eye.


• They have a wide range of wavelengths, which determine the color of light.


• Light waves can travel through a vacuum as well as through various mediums, such as air, water, and glass.


• They can be reflected, refracted, diffracted, and polarized.


• Light waves also exhibit properties of both particles and waves, known as the wave-particle duality.

Therefore, the correct answer is A: Electromagnetic waves.

The iris consists of two sheets of smooth muscle with contrary actions : expansion and contraction. These muscle control the size of the pupil and thus determine how much light reaches the sensory tissues of the retina.

When shooting sports the frame rate needs to be much higher than 24. frames per second remember that to slow down footage. it's explosions or cellular division filming for science usually means shooting at a higher framerate more. frames researchers can better study their subject.

The least distance up to which we can see the objects clearly without any strain is called least distance of distinct vision.In old age least distance is about 25cm.

The correct option is Option B.

The phenomenon of light responsible for the working of the human eye is refraction.

The angle through which a ray of light turns on passing through a prism is called the Angle of Deviation.
Explanation:
When a ray of light passes through a prism, it undergoes refraction (bending) due to the change in speed as it enters a different medium. This refraction causes the ray of light to change its direction.
The angle through which the ray of light is deviated from its original path is known as the Angle of Deviation. It is measured between the incident ray and the emergent ray of light.
Here is a detailed explanation of the angles involved in the passage of light through a prism:
1. Angle of Incidence: This is the angle between the incident ray and the normal (perpendicular) to the surface of the prism at the point of incidence.
2. Angle of Emergence: This is the angle between the emergent ray and the normal to the surface of the prism at the point of emergence.
3. Angle of Deviation: This is the angle between the incident ray and the emergent ray of light. It is the difference between the angle of incidence and the angle of emergence.
The angle of deviation depends on the refractive index of the prism and the angle of incidence. Different materials and angles of incidence will result in varying angles of deviation.
In conclusion, the angle through which a ray of light turns on passing through a prism is called the Angle of Deviation.

Definition of Color Blindness
Color blindness, also known as color vision deficiency, is a condition in which a person is unable to differentiate between certain colors. It is a typically inherited condition, although it can also be caused by certain diseases or eye injuries.
Factors to Determine Color Blindness
Color blindness is determined by a person's inability to perceive specific colors or a difficulty in differentiating between them. It does not affect a person's ability to see in the dark or in the light.
When is a person considered color blind?
A person is considered color blind when they cannot differentiate between colors accurately. This can manifest in various ways, such as:
- Inability to distinguish between certain colors, especially red and green.
- Difficulty identifying shades or hues of certain colors.
- Seeing colors as dull or washed out.
- Confusing certain colors with others.
Common Tests for Color Blindness
There are several tests that can be conducted to determine color blindness, such as:
- Ishihara color plates: This test involves identifying numbers or patterns within a series of colored circles.
- Farnsworth-Munsell 100 hue test: This test measures a person's ability to arrange color chips in a specific order.
- Anomaloscope: This device allows individuals to adjust the intensity of different colors to match one another.
Treatment and Coping Strategies
Unfortunately, there is no cure for inherited color blindness. However, people with color blindness can employ certain strategies to cope with the condition, such as:
- Using color-coded labels or markers.
- Relying on texture or pattern cues to distinguish between objects.
- Seeking assistance from devices or apps that can help identify colors.
Conclusion
Color blindness is a condition characterized by an individual's inability to differentiate between certain colors accurately. It is not related to a person's ability to see in the dark or in the light. Testing for color blindness can be done using various methods, and while there is no cure, individuals can develop coping strategies to manage their color vision deficiency.

Since the person can't read an object at a distance of 50 cm, therefore focal length must be 0.5 m. We know that ; 
P = 1/f , hence, P = 1/0.5 = 2 dioptre. 

What Causes Astigmatism?
Astigmatism is a common vision problem that occurs when the cornea or lens of the eye is irregularly shaped. This irregular shape prevents light from focusing properly on the retina, resulting in blurred or distorted vision. The exact cause of astigmatism is not fully understood, but there are several factors that may contribute to its development.
Causes of Astigmatism:
1. Varying Curvature in Horizontal Lines:
- One possible cause of astigmatism is an uneven curvature of the cornea or lens in the horizontal meridian.
- This means that the cornea or lens is steeper in one direction (horizontal) than in the other (vertical), causing light to focus differently in each direction.
- This can result in blurred vision at both near and far distances.
2. Varying Curvature in Vertical Lines:
- Another possible cause of astigmatism is an uneven curvature of the cornea or lens in the vertical meridian.
- This means that the cornea or lens is steeper in one direction (vertical) than in the other (horizontal), causing light to focus differently in each direction.
- Similar to horizontal astigmatism, this can result in blurred vision at both near and far distances.
3. Combination of Both:
- In some cases, astigmatism can be caused by a combination of varying curvatures in both the horizontal and vertical meridians.
- This means that the cornea or lens has irregularities in multiple directions, leading to distorted vision in various orientations.
4. Other Factors:
- Astigmatism can also be associated with other eye conditions, such as keratoconus (cone-shaped cornea) or corneal scars.
- In some cases, astigmatism may be present from birth (congenital) or develop later in life due to eye injury, surgery, or certain diseases.
Conclusion:
In conclusion, the cause of astigmatism is typically an irregular shape of the cornea or lens, resulting in varying curvature in horizontal, vertical, or both directions. It is important to consult an eye care professional for a comprehensive eye examination to determine the exact cause and severity of astigmatism, as well as to discuss appropriate treatment options.

The bending of light as it passes from one medium to another is called refraction. The angle  and wavelength at which the light enters a substance and the density of that substance determine how much the light is refracted. The bending occurs because light travels more slowly in a denser medium. Hence, by a glass prism as well as a rectangular glass slab.

Dispersion:
- Dispersion is the phenomenon where a beam of light splits into its component colors when passing through a prism.
- This occurs because different colors of light have different wavelengths and thus refract at different angles when passing through a medium like a prism.
- The prism acts as a triangular glass block that refracts the light and separates it into its constituent colors.
- The process of dispersion is the basis for many optical phenomena, including the formation of rainbows and the creation of spectra in spectroscopy.
- The dispersion of light allows scientists to study and analyze the different wavelengths and colors present in a light source.
Reflection:
- Reflection is the phenomenon where light bounces off a surface and changes direction.
- While reflection can occur when light interacts with a prism, it is not the main process responsible for splitting the light into its component colors.
- Reflection is more commonly associated with the bouncing of light off smooth surfaces, such as mirrors or shiny objects.
Refraction:
- Refraction is the bending of light as it passes from one medium to another, such as from air to glass or water.
- Refraction plays a crucial role in the phenomenon of dispersion.
- As light enters a prism, it slows down and changes direction due to the change in density between the air and the glass.
- The change in direction, or bending, of the light is what causes the separation of colors.
Spectrum:
- A spectrum refers to the range of colors produced when light is dispersed by a prism or other means.
- The spectrum is a continuous sequence of colors, ranging from red to violet, with all the colors of the rainbow in between.
- Each color in the spectrum corresponds to a specific wavelength of light.
- The study of spectra and the analysis of the different wavelengths of light can provide valuable information about the composition and properties of light sources.
In conclusion, when a light passes through a prism, it splits into its component colors due to the phenomenon of dispersion. This process involves the refraction of light as it enters and exits the prism, causing the different colors to bend at different angles and separate. The resulting sequence of colors is known as a spectrum.

Observation of Sky Color from the Moon Surface:
The observed color of the sky as seen from the Moon surface is black. Here's a detailed explanation:
1. Absence of Atmosphere:
- The Moon does not have an atmosphere like Earth.
- Earth's atmosphere scatters sunlight, which results in the blue color of the sky as seen from the surface.
- Since the Moon lacks an atmosphere, there is no scattering of sunlight, and hence the sky appears black.
2. Direct View of Space:
- Without an atmosphere to scatter sunlight, the Moon's surface provides a direct view of space.
- When an astronaut stands on the Moon, they can see the vast expanse of space filled with stars, planets, and the Sun.
- The absence of scattering and atmospheric interference allows for a clearer view of celestial objects.
3. Contrast with Lunar Surface:
- The black color of the sky provides a stark contrast with the grayish color of the Moon's surface.
- This contrast enhances the visibility of the lunar terrain and other features.
4. Astronaut Testimonies:
- Astronauts who have been on the Moon, such as the Apollo mission astronauts, have reported that the sky appears black from the lunar surface.
Conclusion:
The observed color of the sky from the Moon surface is black due to the absence of an atmosphere and the direct view of space. This black sky provides a striking contrast with the grayish lunar surface and allows for a clear view of celestial objects.

What is spectrum-
The spectrum refers to the band of colors that is produced when white light is passed through a prism or diffracted by a grating. It is a fundamental concept in physics and optics and is an essential component of understanding the behavior of light.
The band of 7 colors:
- The spectrum is commonly represented as a band of 7 colors: red, orange, yellow, green, blue, indigo, and violet. This is often remembered using the acronym "ROYGBIV".
- Each color in the spectrum corresponds to a different wavelength of light, with red having the longest wavelength and violet having the shortest.
The band of 5 colors:
- This option is incorrect as the spectrum consists of 7 colors, not 5.
The band of 6 colors:
- This option is also incorrect as the spectrum consists of 7 colors, not 6.
None of these:
- This option is incorrect as the correct answer is option A, which states that the spectrum is the band of 7 colors.
In conclusion, the correct answer is option A, which states that the spectrum is the band of 7 colors. This band of colors is a result of the dispersion of white light and is an important concept in physics and optics.

When a person is suffering from both myopia and hypermetropia, they have a condition known as astigmatism. To correct this vision problem, bifocal lenses are required. Here's a detailed explanation:
1. Astigmatism:
- Astigmatism is a refractive error that occurs when the cornea (the clear front surface of the eye) is irregularly shaped.
- This irregular shape causes light rays to focus on multiple points instead of a single point on the retina, leading to blurred or distorted vision.
2. Myopia:
- Myopia, also known as nearsightedness, is a common refractive error where distant objects appear blurry while close objects are clear.
- It occurs when the eyeball is too long or the cornea is too curved, causing light to focus in front of the retina instead of directly on it.
3. Hypermetropia:
- Hypermetropia, also known as farsightedness, is a refractive error where close objects appear blurry while distant objects may be clear.
- It occurs when the eyeball is too short or the cornea is not curved enough, causing light to focus behind the retina instead of directly on it.
4. Bifocal Lenses:
- Bifocal lenses have two different optical powers in a single lens.
- The upper portion of the lens corrects myopia by having a concave (minus) power to focus distant objects properly on the retina.
- The lower portion of the lens corrects hypermetropia by having a convex (plus) power to focus close objects properly on the retina.
5. Corrective Lens for Astigmatism:
- Astigmatism requires correction through a cylindrical lens, which has different powers in different meridians to correct the irregular corneal shape.
- Bifocal lenses can be designed with a cylindrical correction as well to address astigmatism along with myopia and hypermetropia.
Therefore, when a person is suffering from both myopia and hypermetropia, bifocal lenses are required to correct their vision. These lenses provide the necessary correction for both conditions, including the additional cylindrical correction for astigmatism.

If you have concerns about your vision or any other health-related issues, it is always recommended to consult with a qualified healthcare professional.

∵ Near point = 75 cm and Power of lens = + 1 D
∴    P = 100 / f ( in cm )
f = 100 / P
= 100 / 1
= 100 cm
The distance of distinct vision v can be found as below.
Using lens formula here ,
1/f  = 1/v - 1/u
⇒ 1/v = 1/f + 1/u
= 1 / 100 + 1 / - 75  =  3 - 4 / 300
= - 1 / 300
v = ₋300 cm
=  - 3m  ( in meters)

The ability of the eye to adjust its focal length is known as accommodation. Since, a nearby object is typically focused at a further distance,the eye accommodates by assuming a lens shape that has shorter focal length.

The maximum focal length of eye lens is 2.5 cm.