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Practice Class 8 Science MCQs on human eye, cornea, retina, mirrors, multiple reflections, periscope, owl vision, and image formation with detailed explanations.
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Q1. The part of the eye which is a transparent front portion?
Correct Answer: Cornea
Detailed Explanation:
The cornea is the transparent, curved front layer of the human eye. It acts as a protective covering and is the first part of the eye through which light enters. Since the cornea is transparent, it allows light rays to pass through easily and helps focus them toward the retina.
The cornea performs an important role in vision. In fact, most of the bending (refraction) of light entering the eye occurs at the cornea. After passing through the cornea, light travels through the pupil and lens before reaching the retina, where images are formed.
The cornea also protects the delicate inner parts of the eye from dust, germs, and other harmful particles. Because it contains many nerve endings, even a small particle entering the eye can cause irritation or discomfort.
Any damage to the cornea can affect vision significantly. Doctors often examine the cornea during eye checkups because its health is essential for clear vision.
The cornea works together with the lens to focus light correctly. If the cornea is not shaped properly, vision problems such as blurred vision can occur.
Real-Life Examples:
- Eye doctors examine the cornea during vision tests.
- Contact lenses rest directly on the cornea.
- Dust entering the eye often irritates the cornea first.
Important NCERT Points:
- Cornea is the transparent front part of the eye.
- It allows light to enter the eye.
- It helps refract light.
- It protects internal eye structures.
Exam-Oriented Fact:
Most of the eye’s focusing power comes from the cornea.
Quick Revision Line:
The cornea is the transparent front part of the eye that helps focus incoming light.
Q2. Number of images formed by two parallel plane mirrors is?
Correct Answer: Infinite
Detailed Explanation:
When two plane mirrors are placed parallel to each other facing one another, they produce multiple reflections. Light reflected from one mirror strikes the second mirror and gets reflected again. This process continues repeatedly, creating a large number of images.
In theory, the number of images formed by perfectly parallel mirrors is infinite. Each image acts as an object for the opposite mirror, producing another image. As a result, a seemingly endless series of images appears.
This phenomenon is called multiple reflection of light. It occurs because light keeps bouncing back and forth between the mirrors. In practical situations, some images become faint because a small amount of light is absorbed during each reflection, but the principle remains the same.
Multiple reflections are used in several optical devices and decorative arrangements. The concept helps students understand how light behaves when reflected repeatedly.
The number of images formed by mirrors depends on the angle between them. When mirrors are parallel, the angle is zero degrees, resulting in an infinite number of images.
Real-Life Examples:
- Looking between two facing mirrors in a dressing room.
- Decorative mirror arrangements in hotels.
- Optical instruments based on repeated reflections.
Important NCERT Points:
- Parallel mirrors produce multiple reflections.
- Reflected light keeps bouncing between mirrors.
- Theoretical number of images is infinite.
- Each image becomes an object for the next reflection.
Exam-Oriented Fact:
Two plane mirrors placed parallel to each other form infinitely many images.
Quick Revision Line:
Parallel plane mirrors create an infinite number of images due to repeated reflections.
Q3. Human eye forms the image of an object at its?
Correct Answer: Retina
Detailed Explanation:
The retina is the light-sensitive layer located at the back of the eye. It is the part where the final image of an object is formed. The retina contains special cells called rods and cones that detect light and convert it into electrical signals.
When light enters the eye, it passes through the cornea, pupil, and lens. The lens focuses the light onto the retina, creating a real and inverted image. The retina then sends information to the brain through the optic nerve.
The brain interprets these signals and allows us to see objects in their correct orientation. Without the retina, vision would not be possible because the brain would not receive visual information.
The retina works similarly to the film in a traditional camera or the image sensor in a digital camera. It captures incoming light and helps create visual images.
A healthy retina is essential for clear vision. Diseases affecting the retina can cause partial or complete loss of sight.
Real-Life Examples:
- Reading books requires images to form on the retina.
- Cameras and eyes both use image-forming surfaces.
- Eye specialists examine the retina during eye checkups.
Important NCERT Points:
- Retina is located at the back of the eye.
- Images are formed on the retina.
- Rods and cones detect light.
- Optic nerve carries signals to the brain.
Exam-Oriented Fact:
The image formed on the retina is real and inverted.
Quick Revision Line:
The retina is the light-sensitive screen where images are formed in the eye.
Q4. Night birds like Owls have?
Correct Answer: More cones than rods
Detailed Explanation:
According to the given answer key, the correct option is A, but scientifically, owls and most night birds actually have more rods than cones in their retinas. Rod cells are highly sensitive to dim light and help animals see in darkness, while cone cells are responsible for color vision and work best in bright light.
Owls are nocturnal birds, meaning they are active during the night. Their eyes are specially adapted for low-light conditions. A large number of rod cells enables them to detect movement and objects even in very dim environments.
The retina contains two types of photoreceptor cells:
- Rods – Help in night vision and low-light conditions.
- Cones – Help in color vision and daylight vision.
Because of their rod-rich retinas, owls can hunt effectively at night. Their large eyes also collect more light, improving visibility in darkness.
This adaptation gives owls an advantage over many other animals during nighttime hunting.
Real-Life Examples:
- Owls hunt effectively at night.
- Cats also possess excellent night vision.
- Humans see less clearly in darkness due to fewer rod cells.
Important NCERT Points:
- Rods help in dim-light vision.
- Cones help in color vision.
- Nocturnal animals have better night vision.
- Retina contains both rods and cones.
Exam-Oriented Fact:
Rod cells are more sensitive to low-intensity light than cone cells.
Quick Revision Line:
Night vision mainly depends on rod cells present in the retina.
Q5. Which instrument works on the principle of multiple reflections and is used by soldiers in submarines?
Correct Answer: Periscope
Detailed Explanation:
A periscope is an optical instrument that allows a person to see objects that are not in the direct line of sight. It works on the principle of multiple reflections of light. Inside a periscope, mirrors or prisms are arranged at specific angles so that light can be reflected from one end to the observer’s eye.
Periscopes are widely used in submarines. When a submarine remains underwater, sailors use a periscope to observe ships, land, or other objects above the water surface without exposing the submarine.
The basic design of a periscope contains two plane mirrors placed parallel to each other at an angle of 45°. Light from the object reflects off the top mirror, travels through the tube, reflects again from the lower mirror, and finally reaches the observer’s eye.
Periscopes are also used in military vehicles, observation towers, and scientific instruments. The device demonstrates an important practical application of reflection of light.
Understanding the working of a periscope helps students connect scientific principles with real-world technology.
Real-Life Examples:
- Submarines use periscopes for observation.
- Military vehicles may contain periscopes.
- Observation towers sometimes use similar optical systems.
Important NCERT Points:
- Periscope works on multiple reflections.
- Plane mirrors are usually placed at 45°.
- Used in submarines and defense applications.
- Helps observe objects not directly visible.
Exam-Oriented Fact:
A periscope uses repeated reflection of light to transmit images.
Quick Revision Line:
A periscope uses multiple reflections to allow viewing of distant or hidden objects.
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