The Human Eye and the Colourful World - Class 10 Science - Chapter 10 - Notes, NCERT Solutions & Extra Questions
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Notes - The Human Eye and the Colourful World | Class 10 NCERT | Science
The Human Eye and the Colourful World: Comprehensive Class 10 Notes
The human eye is an intricate organ that allows us to perceive the world in all its vibrant colors. Let's delve into the structure and function of the human eye and understand various optical phenomena that contribute to the colorful world around us.
Structure and Function of the Human Eye
Main Parts of the Human Eye:
Cornea: The clear, outermost layer that focuses incoming light.
Iris: The colored part of the eye that controls the size of the pupil.
Pupil: The opening in the center of the iris that regulates the amount of light entering the eye.
Retina: The light-sensitive layer where images are formed.
Optic Nerve: Transmits visual information from the retina to the brain.
How the Human Eye Functions:
The human eye functions much like a camera. Light enters through the cornea and passes through the adjustable pupil. The crystalline lens focuses light onto the retina, where photoreceptor cells translate it into electrical signals sent to the brain via the optic nerve.
Power of Accommodation
Definition and Importance:
The power of accommodation refers to the eye's ability to adjust its lens's focal length to see objects clearly at different distances. This adjustment is achieved by the ciliary muscles altering the lens's curvature.
Least Distance of Distinct Vision:
The least distance of distinct vision is about 25 cm for a young adult. It is the closest distance at which the eye can focus on an object comfortably.
Common Vision Defects and Corrections
Myopia (Near-Sightedness):
Causes: Excessive curvature of the cornea or elongation of the eyeball.
Correction: Using concave lenses to diverge incoming light so that the image forms on the retina.
Hypermetropia (Far-Sightedness):
Causes: Shortened eyeball or reduced curvature of the cornea.
Correction: Using convex lenses to converge light so that the image falls on the retina.
Presbyopia:
Age-Related Changes: Gradual loss of the eye's ability to focus on close objects due to the weakening of ciliary muscles.
Correction: Using bi-focal lenses that have segments for distant and close vision.
Optical Phenomena in Nature
Rainbow Formation:
Rainbows are formed by the dispersion of sunlight by water droplets in the atmosphere. Each droplet acts like a prism, separating the light into different colors.
Blue Colour of the Sky:
The sky appears blue due to the scattering of sunlight by air molecules and other small particles. Shorter blue wavelengths are scattered more prominently than longer red wavelengths.
Atmospheric Refraction:
Atmospheric refraction causes the apparent position of stars to change, resulting in the twinkling effect. It also allows us to see the sun slightly above the horizon even when it is below it.
Scattering of Light
Tyndall Effect:
The Tyndall effect is the scattering of light by particles in a colloid or in very fine suspensions. It explains phenomena like the visibility of a beam of sunlight passing through a room filled with dust particles.
Why is the Sky Blue?:
The blue color of the sky is due to Rayleigh scattering, where shorter (blue) wavelengths are scattered more than longer (red) wavelengths by atmospheric particles.
Eye Health and Vision Care
Cataract:
Cataracts occur when the lens becomes cloudy, leading to blurred vision. It can be corrected through a simple surgical procedure to replace the cloudy lens with an artificial one.
Importance of Eye Donation:
Eye donation can restore vision for individuals with corneal blindness. It is a noble act that can light up a life even after one's death.
Conclusion
Understanding the human eye and the various optical phenomena helps us appreciate the world in all its splendor. Proper eye care and vision correction techniques ensure that we continue to experience this colorful world with clarity.
By comprehending the human eye's capabilities and limitations, we can take better steps to preserve our vision and appreciate the beautiful world around us.
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Extra Questions - The Human Eye and the Colourful World | NCERT | Science | Class 10
A person can see an object beyond 1m but not closer than it. The defect of the person is
A. Myopia
B. Hypermetropia
C. Presbyopia
D. No defect
The correct option is B Hypermetropia
Hypermetropia, also known as far-sightedness, is a common visual defect where an individual can see distant objects clearly but has difficulty focusing on objects that are close up. This specific condition means that the person’s near point is further away than normal, explaining why they cannot see objects clearly if they are closer than 1 meter.
What are the four colours of the spectrum of white light which have a wavelength longer than blue light?
A. Green, Yellow, Orange, Violet
B. Green, Yellow, Indigo, Red
C. Green, Yellow, Orange, Red
D. Green, Yellow, Indigo, Orange
The correct option is C: Green, Yellow, Orange, Red.
The colors listed in the spectrum of white light that exhibit longer wavelengths than blue light include green, yellow, orange, and red. These colors follow blue in the visible spectrum and are arranged in order of increasing wavelength.
Green ($ \approx 495-570 \text{ nm} $)
Yellow ($ \approx 570-590 \text{ nm} $)
Orange ($ \approx 590-620 \text{ nm} $)
Red ($ \approx 620-750 \text{ nm} $)
Thus, the sequence Green, Yellow, Orange, and Red meets the criterion of colors with wavelengths longer than blue.
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The human eye can focus on objects at different distances by adjusting the focal length of the eye lens. This is due to
(a) presbyopia.
(b) accommodation.
(c) near-sightedness.
(d) far-sightedness.
The human eye can focus on objects at different distances by adjusting the focal length of the eye lens due to (b) accommodation. This adjustment is made by changing the curvature of the lens with the help of the ciliary muscles, allowing us to see objects clearly at various distances.
The human eye forms the image of an object at its
(a) cornea.
(b) iris.
(c) pupil.
(d) retina.
The human eye forms the image of an object at its (d) retina. The retina is a layer of tissue at the back of the eye that is sensitive to light. When light passes through the eye's optical system (cornea, pupil, and lens), it is focused to form an image on the retina. The retina then converts this image into electrical signals that are sent to the brain via the optic nerve, allowing us to see.
The least distance of distinct vision for a young adult with normal vision is about
(a) $25 \mathrm{~m}$.
(b) $2.5 \mathrm{~cm}$.
(c) $25 \mathrm{~cm}$.
(d) $2.5 \mathrm{~m}$.
The least distance of distinct vision, also known as the near point, for a young adult with normal vision is approximately $25 , \text{cm}$. This distance represents the closest point at which the eye can focus on an object clearly.
Therefore, the correct answer is:
(c) $25 , \text{cm}$.
The change in focal length of an eye lens is caused by the action of the
(a) pupil.
(b) retina.
(c) ciliary muscles.
(d) iris.
The change in focal length of an eye lens is caused by the action of the ciliary muscles. When these muscles contract or relax, they change the shape of the lens, thus adjusting its focal length. This process is known as accommodation, and it allows the eye to focus on objects at various distances.
So, the correct answer is: (c) ciliary muscles.
A person needs a lens of power -5.5 dioptres for correcting his distant vision. For correcting his near vision he needs a lens of power +1.5 dioptre. What is the focal length of the lens required for correcting (i) distant vision, and (ii) near vision?
To find the focal length of the lens required for correcting vision, we can use the formula relating the power of a lens (in dioptres) to its focal length (in meters):
$$ \text{Power} = \frac{1}{\text{Focal length}} $$
or
$$ \text{Focal length} = \frac{1}{\text{Power}} $$
Here, the focal length ($f$) is measured in meters, and the power ($P$) is in dioptres.
(i) Distant Vision Correction
For distant vision correction, a lens of power (-5.5) dioptres is required.
Substituting the power in the formula gives:
$$ f_{distant} = \frac{1}{-5.5} = -\frac{1}{5.5} , \text{m} $$
The negative sign indicates that a concave lens is required, as it has a diverging effect, which is necessary for correcting myopia (nearsightedness).
(ii) Near Vision Correction
For near vision correction, a lens of power (+1.5) dioptres is required.
Substituting the power in the formula gives:
$$ f_{near} = \frac{1}{1.5} = \frac{2}{3} , \text{m} $$
The positive sign indicates that a convex lens is required, as it has a converging effect, which is necessary for correcting hypermetropia (farsightedness).
Conclusion
Distant vision correction: The focal length of the lens required is $-\frac{1}{5.5}$ meters, indicating a concave lens.
Near vision correction: The focal length of the lens required is $\frac{2}{3}$ meters, indicating a convex lens.
The far point of a myopic person is $80 \mathrm{~cm}$ in front of the eye. What is the nature and power of the lens required to correct the problem?
To correct myopia (nearsightedness), a diverging lens (concave lens) is needed. This lens will help to diverge the incoming light so that the image can be formed on the retina.
The power (P) of a lens in diopters (D) is given by the formula:
$$ P = \frac{1}{f} $$
where (f) is the focal length of the lens in meters. Since the far point of the myopic person is 80 cm in front of the eye, the lens needs to have a focal length of -80 cm to correct the vision. Note that the focal length is negative for a concave lens, indicating its diverging nature.
First, convert the focal length from cm to meters, as the power is expressed in diopters (D) and diopters are measured in meters:
$$ f = -80 , \text{cm} = -0.8 , \text{m} $$
Then, substitute (f) into the equation:
$$ P = \frac{1}{-0.8} = -1.25 , \text{D} $$
Therefore, the required lens to correct the myopic person's vision has a power of -1.25 diopters and is a concave lens.
Make a diagram to show how hypermetropia is corrected. The near point of a hypermetropic eye is $1 \mathrm{~m}$. What is the power of the lens required to correct this defect? Assume that the near point of the normal eye is $25 \mathrm{~cm}$.
To correct hypermetropia (far-sightedness), a convex lens is used. This is because the eye lens of a hypermetropic person focuses the image of near objects beyond the retina. A convex lens helps by converging the light rays before they enter the eye, so that the image forms on the retina.
Diagram Illustration:
Calculating the Power of the Lens:
To calculate the power of the lens required to correct this defect, we use the formula:
$$ P = \frac{1}{f} $$
Where (P) is the power of the lens in diopters (D) and (f) is the focal length of the lens in meters.
The lens should be able to form an image at the near point of the normal eye (25 cm or 0.25 m) from an object placed at the near point of the hypermetropic eye (1 m).
We want the virtual image to form at the normal near point when the object is at the hypermetropic near point using the lens formula:
$$ \frac{1}{f} = \frac{1}{v} - \frac{1}{u} $$
Where:
(f) is the focal length of the lens.
(v) is the image distance (for a normal eye, the near point is at (-0.25) m, (v) is negative because the image is formed on the same side as the object).
(u) is the object distance (for a hypermetropic eye, the near point is (+1) m).
The formula simplifies to:
$$ \frac{1}{f} = \frac{1}{-0.25} - \frac{1}{1} $$
Solving for (f), we can find the power ((P)) of the lens. Let's calculate it.
The power of the lens required to correct this hypermetropic defect is -5 diopters (D). Note that the negative sign denotes the use of a convex lens, but when referring to the power needed to correct for farsightedness (hypermetropia), we generally imply positive diopters. Therefore, the correct power is +5 D.
Why is a normal eye not able to see clearly the objects placed closer than $25 \mathrm{~cm}$ ?
The normal eye is not able to see objects clearly when they are placed closer than (25 , \text{cm}) because of the limitations of the eye's focusing mechanism. The eye focuses light using the lens, which changes shape to adjust the focal distance – a process known as accommodation. However, there is a limit to how much the lens can change its shape to increase its curvature for focusing light from very close objects onto the retina.
When an object is closer than about $25 , \text{cm}$ (the near point for a normal eye), the lens cannot become curved enough to bring the light rays from the object to a focus on the retina. Instead, the focal point falls behind the retina, causing the image to appear blurred. This minimum distance where the eye can focus on an object clearly without strain is referred to as the "near point" of the eye. For most young people with normal vision, the near point is around $25 , \text{cm}$.
As people age, the lens becomes less flexible, a condition known as presbyopia, making it more difficult to focus on close objects, and the near point gets further away.
What happens to the image distance in the eye when we increase the distance of an object from the eye?
When the distance of an object from the eye is increased, the image distance within the eye remains essentially constant. This is because the image formed by the eye's lens is always projected on the retina, which does not change its position. Instead, the eye adjusts its focal length to accommodate for changes in the object's distance, a process known as accommodation.
For closer objects, the ciliary muscles contract, causing the lens to become more curved (thicker), increasing its optical power, and enabling the formation of a clear image on the retina.
For distant objects, the ciliary muscles relax, allowing the lens to become less curved (thinner), decreasing its optical power, thus forming a clear image of the distant object on the retina.
These adjustments ensure that despite changes in the object distance, the image distance within the eye effectively remains constant, focusing the image on the retina. This process allows us to see objects clearly at different distances.
Why do stars twinkle?
Stars twinkle due to a phenomenon called atmospheric refraction. When starlight enters Earth's atmosphere, it passes through layers of air with varying temperatures and densities. This causes the light path to bend or refract. As the temperature and density of the air layers constantly change (due to wind, temperature gradients, and other factors), the bending of the light also changes. This results in the star's light appearing to change in brightness and position rapidly, which we perceive as twinkling.
This twinkling effect is more pronounced for stars near the horizon than for those overhead because light from stars near the horizon passes through more air and is refracted more. Additionally, planets usually don't twinkle as much because they appear as disks with a larger apparent size than stars (which appear as point sources of light), so the variations in brightness and position due to atmospheric refraction average out more for planets.
Explain why the planets do not twinkle.
Planets do not twinkle like stars do due to differences in their apparent sizes as seen from Earth. This difference in behavior is primarily due to two main factors: apparent size and light path distortion caused by Earth's atmosphere.
Apparent Size: Stars are incredibly far away from Earth, so they appear as point sources of light—tiny dots in the sky. Planets, being much closer to Earth, have a larger apparent size. They appear as tiny disks rather than points.
Atmospheric Turbulence: The atmosphere of the Earth is constantly moving and changing temperature. This causes the light from celestial objects to bend and scatter as it passes through, a phenomenon known as atmospheric refraction.
For point sources of light like stars, this bending and scattering cause the stars' light to change intensity and color rapidly, making them appear as if they are twinkling.
For planets, because they have a larger apparent size (their light comes from a 'disk' rather than a point), the scattering and bending effects average out across their disk. Different parts of their light are distorted in slightly different ways at the same time, effectively cancelling out the twinkling effect.
In summary, planets do not twinkle because their larger apparent size compared to stars allows them to present a more stable appearance through the atmospheric turbulence of Earth.
Why does the sky appear dark instead of blue to an astronaut?
The sky appears dark instead of blue to an astronaut because of the absence of a substantial atmosphere in space. On Earth, the sky appears blue during the day due to a phenomenon known as Rayleigh scattering.
Here's how it works:
Rayleigh scattering occurs because molecules and small particles in Earth's atmosphere scatter sunlight in all directions.
Shorter wavelengths of light (blue and violet) are scattered more than longer wavelengths (such as red).
Our eyes are more sensitive to blue light, and some of the violet light gets absorbed by the upper atmosphere and also gets scattered away in other directions more than blue light. That's why we perceive the sky as blue.
In the vacuum of space, where astronauts orbit the Earth or travel, there is no atmosphere to scatter sunlight. Without any molecules to scatter the sunlight, the sky appears to be a dark, black void, even though the sun itself can be incredibly bright. This stark contrast between the bright light from the sun and the darkness of space creates the dark sky perceived by astronauts.
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Ask Chatterbot AIExtra Questions and Answers - The Human Eye and the Colourful World | NCERT | Science | Class 10
Answer briefly:
(a) How do you perceive the colour of an object?
(b) Which part of our body helps us in maintaining body balance?
(c) How does the eye regulate the amount of light that falls on the retina?
(a) Color perception in humans is facilitated by specialized cells in the retina known as cone cells. There are three types of cone cells, each sensitive to different wavelengths of light: one type for red light, one for green light, and one for blue light. The signals from these cells combine to allow us to perceive a spectrum of colors.
(b) The inner ear plays a crucial role in maintaining body balance. It contains the cochlea and three semi-circular canals, which are specifically designed to help detect and manage balance.
(c) The amount of light that enters the eye is regulated by the pupil, a small opening surrounded by the iris. The pupil dilates (expands) in low light and constricts (contracts) in bright light to control the light intensity reaching the retina.
Which of the following is not a property of water?
A. Colourless
B. Odourless
C. Tasteless
D. Colourful
The correct option is D. Colourful.
Water is a vital natural resource on Earth, characterized by being colourless, tasteless, and odourless. Therefore, the description of water as "colourful" is inaccurate.
What is the near and far point of a normal eye?
The near point of the eye, known as the least distance of distinct vision, is the minimum distance at which objects can be seen clearly without strain. For a young adult with normal vision, this is typically around $25 \text{ cm}$.
Conversely, the far point refers to the farthest point up to which objects can be clearly seen. In a normal eye, this is effectively infinity. Thus, a normal eye can clearly see objects that are anywhere between 25 cm and infinity.
Why are particles not seen in colloids?
A) Particle size between $1 \mathrm{~nm} - 1000 \mathrm{~nm}$
B) Particle size $<1 \mathrm{~nm}$
C) Particle size $>1000 \mathrm{~nm}$
D) Particle size between 1nm - $10000 \mathrm{~nm}$
The correct answer is A) Particle size between $1 \mathrm{~nm}$ and $1000 \mathrm{~nm}$.
Colloidal particles are in the size range that lies between the visible (>1000 nm) and the submicroscopic (<1 nm) range. This makes them not visible to the naked eye, as they are smaller than the wavelengths of visible light, which prevents light scattering that could make them visible.
Why is blind spot devoid of vision?
The blind spot refers to a specific small area in the visual field of each eye, aligning with the location of the optic disk (also referred to as the optic nerve head) on the retina. This area lacks photoreceptors (such as rods and cones), the cells necessary for converting light into neural signals. As a result, the optic disk is incapable of image detection, leading to an absence of vision in this part of the visual field.
Raw tomato and unripe chillies are green. During ripening, the chlorophyll degenerates and the masked red takes over.
During the ripening process of raw tomatoes and unripe chillies, the previously dominant chlorophyll pigment breaks down. This pigment, responsible for the green color, is found in structures called chloroplasts within the plant cells. As chlorophyll degenerates, the masked red pigments, which were present but not visible, become prominent, changing the color of the fruit from green to red.
What is the function of the choroid in the human eye? Explain in detail.
The choroid or choroidea serves as the vascular layer of the eye, positioned between the retina and the sclera. It is made up of connective tissues and varies in thickness: approximately $$0.2 , \text{mm}$$ at the back of the eye and narrows to about $$0.1 , \text{mm}$$ toward the front.
A critical function of the choroid is to supply oxygen and nourishment to the outer layers of the retina. It forms part of the uveal tract, together with the ciliary body and iris, contributing to the overall health and functionality of the eye.
Which type of epithelium is found in the cornea of the eye?
A) Squamous epithelium
B) Stratified epithelium
C) Cuboidal epithelium
D) Columnar epithelium
The correct answer to the question is Option B: Stratified epithelium.
The epithelium that is found in the cornea of the eye is characterized as stratified epithelium. This type of epithelium consists of multiple layers of cells, which is essential for providing the necessary protection and resistance required in such a delicate and exposed area as the eye.
A lens has a focal length of $-10 \text{ cm}$. What is the power of the lens and what is its nature?
The focal length given for the lens is $ f = -10 \text{ cm} $, which indicates a negative focal length. Therefore, this lens is a concave lens, meaning it is diverging in nature.
To find the power of the lens, we first convert the focal length from centimeters to meters: $$ f = -10 \text{ cm} = -0.1 \text{ m} $$
The formula for calculating the power ($ P $) of a lens is: $$ P = \frac{1}{f} $$
Substituting the value of $f$ into the formula gives: $$ P = \frac{1}{-0.1} = -10 \text{ diopters} (D) $$
Thus, the lens has a power of $ \boldsymbol{-10 \text{ D}} $, confirming it as a diverging concave lens.
Colour blindness is due to a defect in:
A) Rods and cones
B) Rods
C) Cones
D) Rhodopsin
The correct answer is C) Cones.
Color blindness is primarily attributed to issues with the cone cells in the eyes. These cells are responsible for detecting color. If one or more types of cone cells are deficient, it results in color blindness.
Define Braille, cone cell, and rod cell.
Braille: Braille is a written language for blind people, characterized by patterns of raised dots that are felt with the fingertips. This system allows individuals who are visually impaired to read by touch.
Cone Cells: Cone cells, or simply cones, represent one of three types of photoreceptor cells found in the retina of mammalian eyes, such as the human eye. These cells are essential for color vision and operate best under bright light conditions. Cone cells are heavily populated in the fovea centralis, a 0.3 mm diameter area in the retina devoid of rod cells where cones are densely packed. They are significantly fewer in number towards the peripheral areas of the retina. The human eye contains approximately six to seven million cone cells, concentrated primarily around the macula. These findings were first recorded in 1935 by Osterberg.
Rod Cells: Rod cells are another type of photoreceptor cell located in the retina of the eye, pivotal for functioning under low-light conditions. In contrast to cone cells, rods are mostly situated at the outer edges of the retina and play a significant role in peripheral vision. The human retina contains about 90 million rod cells. Rod cells are more sensitive than cone cells and are almost exclusively responsible for night vision. However, they contribute minimally to color vision, which explains why colors appear less vivid in low-light conditions.
Our eyes detect light in:
A. The simple form of a particular colour.
B. RGB form: Red, Blue, Green form.
C. ROYGBIV, rainbow colour form.
D. None of these ways.
The correct answer is C. ROYGBIV, rainbow colour form.
Our eyes are capable of perceiving light primarily in the spectrum of the seven colors of the rainbow, represented by the acronym VIBGYOR, which stands for Violet, Indigo, Blue, Green, Yellow, Orange, and Red. Each of these colors has a specific wavelength and frequency, which our eyes are tuned to detect.
Statement 1: Deafness is caused due to rupturing of the pinna. Statement 2: Ciliary muscles regulate the size of the pupil.
A) Statement 1 is true and statement 2 is false.
B) Statement 1 is false and statement 2 is true.
C) Both the statements are true.
D) Both the statements are false.
The correct option is D) Both the statements are false.
Statement 1 is incorrect because deafness is typically not caused by rupturing of the pinna. The pinna is the external part of the ear. Significant hearing loss often results from damage to the tympanic membrane (eardrum) or other internal structures, not merely the external part. Conditions like loud noises, poking the eardrum, or sudden pressure changes can result in eardrum ruptures which impact hearing.
Statement 2 is incorrect as well. It is the iris that regulates the size of the pupil, not the ciliary muscles. The ciliary muscles are responsible for changing the shape of the lens to focus light on the retina, a process known as accommodation.
Which of the following patterns can be observed when we see the three traffic lights at a traffic signal?
A) Number Pattern
B) Colour Pattern
C) Language Pattern
D) No pattern can be seen.
The correct option is B) Colour Pattern.
Traffic lights consistently follow a preset sequence of colors: red, yellow, green, and then back to yellow before returning to red. This cycle repeats itself, establishing a recognizable color pattern. Thus, it is clear that we observe a color pattern at a traffic signal.
When you are looking at the objects closer to the eye, then focal length of the eye:
A) remains the same
B) increases
C) decreases
D) can't say
The correct answer is C) decreases.
When we look at objects that are close to our eyes, the eye's lens adjusts by increasing its curvature and becoming thicker. This adjustment decreases the focal length of the lens to keep the image focused on the retina. This capability of the eye to change the lens' shape and adjust the focal length is known as the power of accommodation.
The change in focal length of an eye lens is caused by the action of the: (a) pupil (b) retina (c) ciliary muscles (d) iris.
The correct answer is (c) ciliary muscles. The focal length of the eye lens is altered by changes in its curvature, which are directly controlled by the contraction and relaxation of the ciliary muscles. These muscles adjust the lens's shape to focus light properly onto the retina, allowing us to see clearly at various distances. Thus, it is the ciliary muscles that are responsible for changes in the focal length of an eye lens.
Choose the option that correctly describes night blindness.
A) No visibility at night
B) Visibility decreases in low light
C) Visibility decreases in daylight
D) Visibility increases during night
The correct option is B) Visibility decreases in low light.
Night blindness, also known as nyctalopia, refers to a condition where an individual's ability to see in low-light or dim environments is impaired. This condition occurs because of the malfunctioning of the rods — the cells in the retina responsible for vision in low light. Contrary to what the name might suggest, night blindness does not render a person completely blind at night but rather significantly decreases their low-light vision. Vitamin A deficiency is a common cause of this condition.
When you keep objects very close to the eye, ciliary muscles
A) Expand
B) Contract
C) Remain the same
D) Reflect all the light
The correct answer is B) Contract.
When objects are brought very close to the eye, the ciliary muscles contract. This contraction allows the eye's lens to increase in curvature, enabling the eye to focus properly on the closer object. This process is essential for maintaining clear vision when observing objects at varying distances.
Which colour is represented by the letter "I" in "VIBGYOR"?
A) Indigos
B) Ink
C) Indigo
D) Indica
The correct option is C) Indigo
Indigo is the color represented by the letter "I" in "VIBGYOR". The acronym VIBGYOR stands for Violet, Indigo, Blue, Green, Yellow, Orange, and Red, which are the colors of the rainbow in descending order of their wavelengths.
In a myopic eye, the image of a distant object is formed in front of the retina and not at the retina itself. Why does this defect arise?
This defect in myopic eyes, where the image of a distant object is formed in front of the retina rather than on it, occurs due to:
Excessive curvature of the eye lens: This leads to a higher refractive power, causing light rays to converge too soon.
Elongation of the eyeball: A longer eyeball causes the focal point of the incoming light to fall short of the retina.
Both conditions prevent light from focusing correctly on the retina, resulting in blurred vision for distant objects.
In the human eye, the power of accommodation is controlled by
A. Ciliary body
B. Cornea
C. Rectar muscles
D. Oblique muscles
The correct answer is A. Ciliary body.
Power of Accommodation: This term refers to the eye's ability to adjust its focal length to clearly focus images of objects at various distances onto the retina. This adjustment is primarily achieved through the action of the ciliary body. The ciliary muscles within this structure alter the shape of the eye lens, which is biconvex and crystalline, enabling the eye to focus on both near and distant objects effectively.
What would be the effect on the image seen by a human if the person had just one eye instead of two?
Having only one eye significantly impacts a person’s ability to perceive depth. Depth perception is crucial for recognizing the three-dimensionality of the surroundings. When depth perception is compromised, various everyday tasks become more challenging since it is difficult to gauge distances accurately. For instance, a step might not be perceived in its full 3D form which might lead to a person not recognizing it as an object that 'stands out,' hence potentially leading to more accidents such as falls.
Moreover, having a single eye also cuts the field of vision in half, further reducing a person's ability to navigate their environment effectively.
If hypothetically humans evolved or were naturally born with one eye, perhaps centrally located on the forehead, the issue of not having peripheral vision would still exist. However, over time, adaptations in behavior and cognition might have evolved to mitigate some of these challenges, making it a new kind of 'normal.'
Which vitamin helps to keep our skin and eyes healthy?
Vitamin A is crucial for promoting good vision, and it is essential in maintaining healthy eyes and skin.
Why can't we see in the dark?
Option 1) Our eyes respond only to sunlight
Option 2) There is no light to reflect from the objects
Option 3) Power of eye is reduced
Option 4) Objects absorb all the light in the dark
Correct Option: B
Our eyes need light to observe our surroundings. We see objects when light enters our eyes, either emitted or reflected by the objects. Here's a more detailed breakdown:
Light Entry: For vision, light must reach our eyes.
Light Emission or Reflection: This light can either be emitted by the object itself or be reflected off the object.
Eye Sensitivity: Our eyes respond to light from any source, not just sunlight.
Additionally, some animals, such as cats and owls, have the ability to see better in the dark because their pupils can open wider, allowing more light to enter their eyes compared to human eyes.
In complete darkness, there is no light to reflect off objects, which is why we can't see them. Therefore, the correct option is Option 2: There is no light to reflect from the objects.
The colour of scattered light depends upon the size of the scattering particles.
True
False
The correct option is A: True
The color of scattered light is indeed dependent on the size of the scattering particles. Very fine particles predominantly scatter blue light, while larger particles scatter light of longer wavelengths. If the scattering particles are sufficiently large, the scattered light may appear white because light rays of all wavelengths are scattered, and together they constitute white light.
The animals which are prey have:
(a) two eyes at the front
(b) two eyes at the back
(c) two eyes on the sides
(d) one eye at the front and one on the side
The animals which are prey have:
(c) two eyes on the sides
Prey animals often have eyes positioned on the sides of their heads, which allows for a wider field of vision. This adaptation helps them to better detect predators approaching from various directions.
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