NTSE Level Test: The Human Eye & the Colourful World - Class 10 MCQ

The light must be travelling from a more dense medium into a less dense medium the angle of incidence must be greater than the critical angle. 

As the angle of incidence increases, the angle of refraction also increases proportionally to the increase of incidence.
( By Snell's law) .

The lateral displacement of an incident ray passing out of a rectangular glass slab  is directly proportional to the thickness of glass slab, angle of incidence, and refractive index however it is inversely proportional to the wavelength of incident light. 

Incorrect Statement: D: Sun is visible 2 minutes after sunrise and 2 minutes before sunset.
Detailed
The correct statement among the given options is D. The sun is not visible exactly 2 minutes after sunrise and 2 minutes before sunset. This statement is incorrect due to the following reasons:
1. Sunrise and Sunset:
- Sunrise is the moment when the upper edge of the sun appears on the horizon in the morning.
- Sunset is the moment when the upper edge of the sun disappears below the horizon in the evening.
- These moments vary based on the geographical location and time of the year.
2. Atmospheric Conditions:
- The visibility of the sun after sunrise and before sunset depends on various atmospheric conditions such as the presence of clouds, haze, pollution, and geographical features like mountains or tall buildings.
- These factors can affect the visibility of the sun and the duration before or after the official sunrise or sunset.
3. Twilight:
- Twilight is the period before sunrise and after sunset when the sun is below the horizon but still illuminates the sky.
- During this time, the sky can be lit to varying degrees, creating a period of dim light even though the sun is not visible.
Therefore, the statement that the sun is visible exactly 2 minutes after sunrise and 2 minutes before sunset is incorrect. The visibility of the sun depends on various factors and can vary from location to location.

The person developing nearsightedness is experiencing:
A: The focal length of eye lens has decreased
- Nearsightedness, or myopia, occurs when the eye is unable to focus light properly, resulting in blurred vision for distant objects.
- The focal length of the eye lens refers to its ability to bend light rays and bring them to a clear focus on the retina.
- In nearsightedness, the focal length of the eye lens decreases, causing the light rays to converge in front of the retina instead of directly on it.
- This leads to the inability to see distant objects clearly.
B: The size of eye ball has elongated
- Another factor contributing to nearsightedness is the elongation of the eye ball.
- When the eye ball becomes longer from front to back, it causes a mismatch between the length of the eye and its focusing power.
- This elongation results in the focal point falling in front of the retina, leading to nearsightedness.
C: Power of eye lens has increased
- Nearsightedness can also occur if the power of the eye lens increases excessively.
- The eye lens plays a crucial role in focusing light onto the retina.
- If the power of the eye lens becomes stronger, it can cause the light to focus in front of the retina, causing nearsightedness.
D: All of these
- In most cases, nearsightedness is caused by a combination of factors, including a decrease in the focal length of the eye lens, elongation of the eye ball, and an increase in the power of the eye lens.
- Therefore, the correct answer is D: All of these.
In conclusion, the development of nearsightedness is influenced by multiple factors, including changes in the focal length of the eye lens, elongation of the eye ball, and an increase in the power of the eye lens. These factors result in the inability to focus light properly onto the retina, leading to blurred vision for distant objects.

Twinkling of stars is due to atmospheric refraction. Distant star acts like a point source of light. When the Starlight enters the earth's atmosphere it undergoes refraction continuously, due to changing refractive index ie. From rarer to denser medium. 

Why are danger signals red in colour?
There are several reasons why danger signals are red in colour:
1. Red colour is least scattered:
- Red light has the longest wavelength among all visible light.
- It is least scattered by particles in the atmosphere, allowing it to travel long distances without losing much intensity.
- This makes it highly visible, even in foggy or smoky conditions.
2. Wavelength of red colour is less than that of other colours:
- The wavelength of red light is around 620-750 nanometers, which is longer than the wavelengths of other colours in the visible spectrum.
- This longer wavelength allows red light to penetrate through obstacles and be perceived more easily.
3. Red colour is eye-catching:
- Red is a highly noticeable colour that naturally draws attention.
- It stands out against many backgrounds and is easily distinguishable from other colours, making it an effective choice for warning signals.
4. Red has cultural associations with danger:
- Red has long been associated with danger, caution, and warning in many cultures.
- This cultural symbolism reinforces the effectiveness of red as a colour choice for danger signals.
In conclusion, danger signals are red in colour because red light is least scattered, has a longer wavelength, is eye-catching, and has cultural associations with danger. These factors make red an ideal colour for effectively communicating warnings and ensuring visibility in hazardous situations.

Optical fibre is used for:
- Communication over long distances: Optical fibre is primarily used for long-distance communication because it can transmit large amounts of data quickly and efficiently. It is widely used in telecommunications networks, including telephone systems, internet connections, and cable television.
- Medical applications: Optical fibre is also used in various medical applications. It is commonly used in endoscopy procedures, where a thin, flexible optical fibre is inserted into the body to visualize and diagnose internal organs. Optical fibre is also used in laser surgery and photodynamic therapy.
- Biomedical engineering: Optical fibre plays a crucial role in biomedical engineering. It is used in the development of medical devices and sensors, such as fibre-optic biosensors for detecting various substances in the body. Optical fibre is also used in imaging techniques, such as optical coherence tomography (OCT), which provides high-resolution images of biological tissues.
- All of these: Optical fibre is used in all of the above-mentioned applications. It is a versatile technology that has revolutionized communication, healthcare, and various other industries. Its ability to transmit data quickly and accurately over long distances makes it an essential component in modern society.
In conclusion, optical fibre is used for communication over long distances, medical applications, and biomedical engineering. Its high data transmission capabilities and flexibility make it an indispensable technology in various fields.

A lens which can bring an object at infinity to 40 cm is required here. 
So, u = infinity, v = -40 cm 
We know, 1/f  = 1/ v - 1/u 
1/ f  = 1/-40 - 1/infinity
So, f = -40 cm = -0. 4 m
Power of lens, P = 1/ f = 1/ -0. 4 = -2. 5 D

Bees are sensitive to Ultraviolet light
- Bees have the ability to see ultraviolet light, which is invisible to the human eye.
- The ultraviolet spectrum is shorter than the visible spectrum, and bees can detect wavelengths ranging from 300 to 400 nanometers.
- Bees use their sensitivity to ultraviolet light for various purposes, such as finding nectar and pollen in flowers.
- Many flowers have patterns or markings that are only visible in ultraviolet light, guiding bees to the nectar.
- Bees can also see the ultraviolet patterns on other bees, helping them identify each other and maintain social cohesion within the hive.
- The ability to see ultraviolet light is an important adaptation for bees, as it allows them to navigate their environment and find food sources more effectively.
Conclusion: Bees are sensitive to ultraviolet light, which plays a significant role in their foraging and social behaviors.

Statement A: Improper functioning of rod shaped cells causes colour blindness
- Rod shaped cells, also known as rods, are responsible for vision in low light conditions and the perception of black and white.
- Colour blindness, also known as color vision deficiency, is a condition where an individual has difficulty distinguishing certain colors.
- The main cause of color blindness is the malfunctioning or absence of cone cells, which are responsible for color vision.
- Rod cells do not play a significant role in color vision, so their improper functioning would not directly cause color blindness.
- Therefore, Statement A is false.
Statement B: The focal length of the human eye can be increased or decreased
- The focal length is the distance between the lens of an optical system and its focus point.
- In the human eye, the cornea and the lens work together to focus light onto the retina.
- The shape of the lens can be adjusted to change the focal length and bring objects into focus at different distances.
- This process is known as accommodation and is controlled by the ciliary muscles.
- When the ciliary muscles contract, the lens becomes thicker, increasing its refractive power and decreasing the focal length.
- When the ciliary muscles relax, the lens becomes thinner, decreasing its refractive power and increasing the focal length.
- Therefore, the focal length of the human eye can be increased or decreased.
- Statement B is true.
Based on the explanations above, the correct answer is:
Answer: C. Statement B is true, A is false

The boy is suffering from Myopia (short-sightedness) because he uses spectacles with a negative focal length of -50cm. Myopia is a condition in which a person can see nearby objects clearly but has difficulty seeing distant objects.
Explanation:
- Myopia is a common vision problem where the light entering the eye focuses in front of the retina instead of directly on it. This can be caused by the eyeball being too long or the cornea being too curved.
- Focal length is a measure of how strongly a lens converges or diverges light. Negative focal length indicates that the lens is a diverging lens, which is used to correct myopia.
- In myopia, the light rays from distant objects converge in front of the retina, resulting in a blurred image.
- By using spectacles with a negative focal length (diverging lens), the light rays are diverged before entering the eye, allowing them to focus correctly on the retina and improving distant vision.
Therefore, based on the information provided, the boy's condition corresponds to myopia, and the correct answer is A: Myopia.

Explanation:
When we increase the distance of an object from the eye, the image distance in the eye remains the same. This can be explained by understanding the functioning of the eye.
The human eye works by focusing light rays from an object onto the retina, which is the light-sensitive layer at the back of the eye. The lens in the eye adjusts its shape to ensure that the light rays converge at a specific point on the retina, forming a clear image.
Key Points:
- The image distance refers to the distance between the lens and the image formed on the retina.
- When an object is moved closer to the eye, the lens adjusts its shape to maintain focus, causing the image distance to decrease.
- Conversely, when an object is moved farther away from the eye, the lens again adjusts its shape to maintain focus, keeping the image distance the same.
- This is because the lens has the ability to change its focal length, allowing it to focus light from objects at different distances onto the retina.
- The ability of the lens to adjust its shape and focal length is known as accommodation.
Therefore, when the distance of an object from the eye is increased, the image distance in the eye remains the same due to the accommodation of the lens to maintain focus.

u = -75 cm 
P = 1/f 
f = 1 m = 100 cm 
So, by lens formula ; 
1/f = 1/v - 1/ u 
So, 1/ v = 1/f +1/u
1/ v =  1/100 + (-1/75) 
1/v = -1/300 
v = -300 cm

Sine(Critical angle) = 1/refractive index so sin 45 = 1/1.41/1.4 = 1/ refractive index hence refractive index = 1.44

The ability of eye lens to focus near and far objects is called power of accommodation. 
Nearest point which the eye can see clearly is called near points. 
The farthest point to which the eye see clearly is known as far point. 
Least distance of distinct vision is the minimum distance at which eye can see the object clearly without strain.

A medium bounded by two plane refracting surfaces at an angle is known as prism. 
Splitting up of white light into its components is called spectrum. 
Scattering of beam of light, when it passes  through colloidal solution is called Tyndall effect. Rainbow is a spectrum of white light when it passes through small rain drops.

Advanced sunrise and delayed sunset are phenomena caused due to atmospheric refraction. In this the sun appears to rise early by 2 minutes and set late by 2 minutes. 
A rainbow is a meteorological phenomena that is caused by total internal reflection refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky.