Class 10 Science Chapter 10 Question Answers - The Human Eye and the Colourful World

Q1: Explain the process of accommodation of the eye. Describe how the shape of the eye lens changes when focusing on a near object and a distant object.
Ans: Accommodation is the ability of the human eye to adjust its focal length to focus on objects at different distances. This process involves changes in the shape of the eye lens. When focusing on a near object and a distant object, the shape of the eye lens changes as follows:
Focusing on a Near Object:

• When the eye is focusing on a near object, the ciliary muscles contract.
• This causes the suspensory ligaments attached to the lens to relax.
• As a result, the lens becomes thicker and more convex, increasing its refractive power.
• The increased curvature of the lens allows for greater bending of light rays, enabling the near object to be focused on the retina.

Focusing on a Distant Object:

• When the eye is focusing on a distant object, the ciliary muscles relax.
• This causes the suspensory ligaments to become taut.
• As a result, the lens becomes thinner and less convex, reducing its refractive power.
• The decreased curvature of the lens allows for less bending of light rays, enabling the distant object to be focused on the retina.

In summary, the process of accommodation involves the contraction and relaxation of the ciliary muscles, which in turn affects the shape of the eye lens. This allows the eye to adjust its focus and form clear images of objects at varying distances.

Q2: Explain the concept of dispersion of light. Describe how a glass prism disperses white light into its component colors and forms a spectrum.
Ans: Dispersion of light refers to the separation of white light into its component colors when it passes through a medium that refracts different colors by different amounts. A glass prism is a classic example of a medium that disperses white light into its component colors, forming a spectrum.
Process of Dispersion and Spectrum Formation:

• White light consists of a mixture of colors with different wavelengths, each corresponding to a different color in the visible spectrum.
• When white light enters a glass prism, it undergoes refraction at both of its surfaces. However, the degree of refraction is different for each color due to their varying wavelengths.
• As a result, different colors deviate from their original path by different angles, causing them to spread out as they emerge from the prism.
• The colors arrange themselves in a specific order: red, orange, yellow, green, blue, indigo, and violet (ROYGBIV). This arrangement is called a spectrum.

Significance and Applications:
The dispersion of light and the formation of a spectrum are fundamental to various optical devices and phenomena. Examples include rainbows, the splitting of light in camera lenses, and the operation of spectrometers used in scientific research to analyze the composition of materials based on the wavelengths of light they absorb or emit.

Q3: Explain the process of formation of a rainbow. Describe how sunlight is refracted, internally reflected, and dispersed in raindrops to create a rainbow.
Ans: A rainbow is a beautiful natural phenomenon that occurs when sunlight is refracted, internally reflected, and dispersed within raindrops in the atmosphere.
The process of forming a rainbow involves the following steps:

• Refraction: When sunlight enters a raindrop, it is refracted (bent) as it passes from air to water. Different colors (wavelengths) of light are refracted by different amounts due to their varying speeds in water.
• Internal Reflection: After refraction, light undergoes total internal reflection within the raindrop. This occurs when the angle of incidence is greater than the critical angle, causing the light to bounce off the inner surface of the raindrop.
• Dispersion: As light undergoes internal reflection, it is also dispersed within the raindrop. Different colors are refracted by varying angles upon exiting the raindrop, causing the light to spread out into a spectrum.
• Multiple Reflections: The dispersed light undergoes further internal reflections and refractions within the raindrop, resulting in the separation of colors and the formation of a circular arc of colored light.
• Emergence: The rainbow's colors emerge from the raindrop and reach the observer's eyes. The observer sees a semicircular arc of colors, with red on the outer side and violet on the inner side.

It's important to note that the observer must be situated with their back to the Sun to observe a rainbow. Raindrops act as tiny prisms, refracting, reflecting, and dispersing sunlight to create the stunning phenomenon of a rainbow in the sky.

Q4: Describe the functioning of a human eye. Explain the role of the cornea, iris, pupil, and retina in the process of vision.
Ans: The human eye is a complex organ that allows us to perceive the world around us through the process of vision. It involves the coordinated functioning of various parts, including the cornea, iris, pupil, and retina.

• Cornea: The cornea is the transparent, outermost layer of the eye. It acts as a protective covering and also plays a significant role in focusing light onto the retina. The cornea refracts light as it enters the eye.
• Iris and Pupil: The iris is the colored part of the eye surrounding the pupil. The iris controls the size of the pupil, which is the central opening of the eye. The size of the pupil changes in response to varying light conditions. In bright light, the iris contracts, reducing the pupil size to limit the amount of light entering the eye. In dim light, the iris relaxes, allowing the pupil to dilate and allow more light to enter.
• Retina: The retina is the innermost layer of the eye and contains photoreceptor cells called rods and cones. These cells are sensitive to light and are responsible for capturing visual information. When light falls on the retina, it triggers a chemical reaction in the photoreceptor cells, generating electrical signals that are transmitted to the brain through the optic nerve.

The process of vision involves the cornea and lens focusing light onto the retina, where the photoreceptor cells capture the image and convert it into electrical signals. These signals are then transmitted to the brain, which processes the information to create the visual perception of the external world.

Q5: Explain the concept of myopia and hypermetropia. Describe how these refractive defects of the eye can be corrected using appropriate lenses.
Ans: Myopia and hypermetropia are two common refractive defects of the eye that affect a person's ability to focus on objects at different distances. These conditions can be corrected using corrective lenses.
Myopia (Nearsightedness):

• In myopia, the eyeball is too long or the cornea is too curved, causing light rays to focus in front of the retina instead of directly on it.
• As a result, distant objects appear blurred, while near objects can be seen more clearly.
• Corrective Lens: A concave lens is used to correct myopia. The concave lens diverges light before it enters the eye, allowing the light to focus properly on the retina.

Hypermetropia (Farsightedness):

• In hypermetropia, the eyeball is too short or the cornea is too flat, causing light rays to focus behind the retina instead of directly on it.
• People with hypermetropia may have difficulty focusing on nearby objects, and distant objects may also appear blurred.
• Corrective Lens: A convex lens is used to correct hypermetropia. The convex lens converges light before it enters the eye, allowing the light to focus properly on the retina.

In both cases, the corrective lens helps to adjust the focal length of the eye, allowing the light to be properly focused on the retina. The lens compensates for the refractive error, allowing the person to see objects clearly at different distances. It's important for individuals with myopia or hypermetropia to have their eyes examined by an optometrist to determine the appropriate prescription for their corrective lenses.

Q6: Explain the phenomenon of persistence of vision. Describe how it is related to the perception of motion in a motion picture.
Ans: Persistence of vision is a phenomenon in which the human eye retains an image for a brief moment after it has disappeared from view. This phenomenon plays a crucial role in the perception of motion in a motion picture.
Perception of Motion in a Motion Picture:

• A motion picture consists of a sequence of individual frames, each containing a slightly different image.
• When these frames are projected onto a screen at a rapid rate (usually 24 frames per second or higher), the persistence of vision causes the brain to blend these individual frames into a continuous and seamless motion.
• The brain interprets the rapid succession of frames as a moving scene, creating the perception of motion.
• This phenomenon is utilized in various forms of visual entertainment, such as movies, animations, and television shows, to create the illusion of movement and bring static images to life.

Q7: Explain the concept of a rainbow. How does the dispersion and internal reflection of sunlight in raindrops lead to the formation of a primary rainbow? Provide a detailed explanation.
Ans: A rainbow is a meteorological phenomenon that results from the dispersion, refraction, and internal reflection of sunlight in water droplets in the atmosphere.
The formation of a primary rainbow involves several optical processes:

• Dispersion: Sunlight is a mixture of different colors with varying wavelengths. When sunlight enters a water droplet, it is refracted, and its colors are separated due to differences in their refractive indices. Dispersion causes the different colors to spread out.
• Internal Reflection: Once inside the water droplet, the dispersed light undergoes multiple internal reflections at the inner surface of the droplet. Total internal reflection occurs when the angle of incidence is greater than the critical angle, causing the light to bounce off the inner surface.
• Refraction: After internal reflection, the light exits the droplet and undergoes another refraction as it transitions from water to air. The refraction bends the light as it exits the droplet.
• Separation and Spectrum Formation: The combination of dispersion, internal reflection, and refraction causes the dispersed light to spread out even further. This results in the formation of a spectrum of colors, with red on the outer edge and violet on the inner edge.
• Observer's Perspective: To see a rainbow, the observer must have the Sun at their back and be facing the area where raindrops are present. The observer's eye receives the dispersed light from numerous raindrops at various angles, creating the semicircular arc of colors that we perceive as a rainbow.

The primary rainbow is the result of one internal reflection within the raindrop. The sequence of dispersion, internal reflection, and refraction working together in each droplet collectively creates the beautiful phenomenon of a primary rainbow in the sky.

Question 8: Describe the working principle of a compound microscope. Explain how the objective lens and the eyepiece lens magnify the image of a specimen.
Ans: A compound microscope is an optical instrument used to magnify small objects or specimens that are not visible to the naked eye. It consists of two main lenses: the objective lens and the eyepiece lens. The working principle of a compound microscope involves the magnification of an image through the combined action of these lenses.
Working Principle:

• Objective Lens: The objective lens is placed close to the specimen and produces a magnified real image. It has a short focal length, allowing it to capture details of the specimen.
• Real Inverted Image: The objective lens forms a real, inverted, and magnified image of the specimen on the other side of the lens.
• Intermediate Image: The real image formed by the objective lens serves as an intermediate image. This image is further magnified by the eyepiece lens.

Magnification by the Objective Lens:

• The magnification produced by the objective lens is determined by the ratio of the angular size of the image to the actual size of the object.
• The objective lens provides the initial magnification of the specimen, making its details visible.

Eyepiece Lens:

• The eyepiece lens is positioned near the observer's eye and acts as a simple magnifying glass.
• Virtual Image: The eyepiece lens magnifies the intermediate image formed by the objective lens, creating a virtual, upright, and further magnified image.
• Combined Magnification: The combined magnification of the compound microscope is the product of the magnification of the objective lens and the magnification of the eyepiece lens.

Total Magnification: The total magnification of the compound microscope is given by the product of the magnification of the objective lens and the magnification of the eyepiece lens.
In summary, the compound microscope uses the objective lens to create a real, inverted, and magnified image of the specimen, which is further magnified by the eyepiece lens to create a virtual, upright, and highly magnified final image for observation.

Q9: Explain the concept of scattering of light. Describe how the blue color of the sky is a result of scattering by air molecules and the reddish-orange hue during sunrise and sunset is a consequence of a longer path of light through the atmosphere.
Ans: Scattering of light is the process by which light is deflected in various directions as it interacts with particles or molecules in a medium. The blue color of the sky and the reddish-orange hue during sunrise and sunset are both outcomes of scattering phenomena in the Earth's atmosphere.
Blue Color of the Sky:

• The Earth's atmosphere contains numerous gas molecules and tiny particles that interact with sunlight.
• Shorter wavelengths of light, such as blue and violet, are scattered more effectively by air molecules than longer wavelengths (red and yellow).
• When sunlight enters the atmosphere, blue light is scattered in all directions by air molecules, resulting in a diffuse blue glow across the sky.
• This phenomenon, known as Rayleigh scattering, is responsible for the blue color of the daytime sky when the Sun is directly overhead.

Reddish-Orange Hue during Sunrise and Sunset:

• During sunrise and sunset, the Sun is positioned near the horizon, and its light has to pass through a larger portion of the atmosphere.
• The longer path through the atmosphere scatters shorter wavelengths (blue and violet) even more, allowing primarily red, orange, and yellow wavelengths to dominate.
• The scattered blue and violet light is effectively removed from the line of sight, causing the remaining sunlight to appear reddish-orange.
• The atmosphere acts as a filter, allowing only longer wavelengths to reach our eyes, creating the warm hues characteristic of sunrise and sunset.
• The phenomenon of scattering contributes to the beautiful array of colors observed in the sky and provides insight into the behavior of light as it interacts with particles in the atmosphere.

Q10: Describe the structure of the human eye. Explain the role of the following parts in the process of vision: cornea, iris, lens, retina, and optic nerve.
Ans: The human eye is a complex sensory organ that allows us to perceive the visual world. It consists of various parts, each playing a crucial role in the process of vision.

• Cornea: The cornea is the transparent outer covering of the eye. It helps focus light onto the retina and acts as a protective barrier against dust and foreign particles. The cornea is responsible for about two-thirds of the eye's total refractive power.
• Iris: The iris is the colored part of the eye that surrounds the pupil. It controls the size of the pupil and regulates the amount of light entering the eye. In bright light, the iris contracts, and in dim light, it expands, adjusting the pupil's diameter.
• Lens: The lens is a transparent, flexible structure located behind the iris. It further focuses light onto the retina by changing its shape through the process of accommodation. The lens adjusts its curvature to focus on objects at varying distances.
• Retina: The retina is the innermost layer of the eye, consisting of photoreceptor cells (rods and cones) that capture light and convert it into electrical signals. These signals are sent to the brain through the optic nerve, initiating the process of vision.
• Optic Nerve: The optic nerve is a bundle of nerve fibers that carries visual information from the retina to the brain. It connects the eye to the brain's visual centers, allowing us to perceive and interpret visual stimuli.

Process of Vision:

• Light enters the eye through the cornea and pupil.
• The lens adjusts its shape to focus the light onto the retina.
• Photoreceptor cells in the retina detect the light and generate electrical signals.
• These signals are transmitted through the optic nerve to the brain.
• The brain processes the signals to create the perception of a visual image.

In summary, the coordinated functioning of the cornea, iris, lens, retina, and optic nerve allows the human eye to capture, transmit, and interpret visual information, enabling us to perceive the world around us.