CBSE Class 7 Science Important Questions Chapter 11 - Light

1. What is light, and why is it essential for vision?
Light is a form of energy that travels in straight lines and allows us to see objects. When light reflects off objects and reaches our eyes, it creates an image, enabling us to see. Without light, vision is not possible as there would be no source to illuminate objects.

2. What is meant by the reflection of light?
Reflection of light is the phenomenon where light bounces off a surface, like a mirror, and changes direction. When light hits a smooth, shiny surface, it reflects at the same angle at which it strikes the surface, following the laws of reflection.

3. Define the laws of reflection.
The laws of reflection state that:

1. The angle of incidence (the angle at which light hits a surface) is equal to the angle of reflection (the angle at which it bounces off).

2. The incident ray, reflected ray, and the normal (line perpendicular to the surface) all lie in the same plane.

4. What is a mirror? Describe its types.
A mirror is a smooth surface that reflects light to form images. There are three main types:

1. Plane mirrors - flat surfaces that produce upright images.

2. Concave mirrors - curved inward and used to focus light.

3. Convex mirrors - curved outward, used to spread light.

5. What is the difference between real and virtual images?
A real image is formed when light rays meet at a point and can be displayed on a screen. It’s usually inverted. A virtual image is formed when light rays appear to meet but do not actually converge; it cannot be projected on a screen and is usually upright.

6. How does a plane mirror form an image?
A plane mirror forms an image by reflecting light rays in a way that makes the image appear as if it is behind the mirror. The image formed is virtual, upright, and the same size as the object, but it is laterally inverted, meaning left and right are reversed.

7. What is lateral inversion?
Lateral inversion is the reversal of left and right in the image formed by a mirror. For example, in a plane mirror, if you raise your right hand, the image seems to raise its left hand. This effect is why letters appear reversed in mirrors.

8. What is a concave mirror, and where is it used?
A concave mirror is a mirror curved inward, like the inside of a bowl. It focuses light rays to a point, creating a real image. Concave mirrors are used in makeup mirrors, telescopes, and headlights as they can magnify and focus light.

9. Describe a convex mirror and its applications.
A convex mirror curves outward, spreading light rays and creating a virtual image that is smaller than the object. It’s commonly used in rearview mirrors in vehicles and security mirrors because it provides a wider field of view.

10. Explain the concept of a focal point in a concave mirror.
The focal point of a concave mirror is the point where parallel light rays converge after reflecting from the mirror’s surface. This point is located along the principal axis, in front of the mirror, and is used to focus light in applications like headlights.

11. What is the refraction of light?
Refraction is the bending of light when it passes from one medium to another, like from air to water. This happens because light changes speed as it enters a different medium. For instance, a straw in a glass of water looks bent due to refraction.

12. Define the lens and its types.
A lens is a transparent object that refracts light rays to either converge or diverge them. The two main types are:

1. Convex lens - thicker at the centre, converges light rays to a focal point.

2. Concave lens - thinner at the centre, diverges light rays outward.

13. How does a convex lens form an image?
A convex lens focuses parallel light rays to a focal point, forming an image. The nature of the image depends on the object’s position. It can form a real, inverted image when the object is beyond the focal point or a virtual, upright image when the object is within the focal point.

14. Explain how a concave lens affects light rays.
A concave lens diverges light rays, spreading them out so that they appear to originate from a point behind the lens. This lens forms a virtual, upright, and smaller image than the object, making it useful in devices like eyeglasses for correcting short-sightedness.

15. What is the dispersion of light?
Dispersion is the splitting of white light into its constituent colours (red, orange, yellow, green, blue, indigo, and violet) when it passes through a prism. This happens because different colours bend at slightly different angles, creating a spectrum.

16. How does a prism create a spectrum?
A prism creates a spectrum by refracting or bending each colour in white light at different angles as the light passes through it. Since each colour has a different wavelength, they spread out to form a rainbow-like pattern known as a spectrum.

17. Describe the structure and function of the human eye.
The human eye is a spherical organ that detects light and sends visual information to the brain. Key parts include the cornea, lens, retina, and optic nerve. Light enters through the cornea, passes through the lens, and focuses on the retina, where signals are sent to the brain to interpret images.

18. What role does the retina play in vision?
The retina is a layer of light-sensitive cells at the back of the eye that captures light and converts it into electrical signals. These signals are sent to the brain through the optic nerve, allowing us to perceive images and colours.

19. What is the blind spot in the human eye?
The blind spot is an area on the retina where the optic nerve connects, lacking light-sensitive cells. This area cannot detect light, so it does not capture any part of an image, resulting in a small area of vision where we are "blind."

20. Explain how we see colours.
We see colours because the retina contains special cells called cones that respond to different wavelengths of light. Each cone is sensitive to red, green, or blue light. The brain processes the signals from these cones to create a full spectrum of colours.

21. What are the primary colours of light?
The primary colours of light are red, green, and blue. By combining these colours in different intensities, we can create a wide range of other colours, which is how screens like TVs and phones display colours.

22. How do convex and concave lenses differ in terms of image formation?
A convex lens converges light rays and can form real, inverted images or virtual, upright images depending on the object's position. A concave lens diverges light rays, always forming a virtual, upright, and smaller image than the object.

23. Why is the sky blue?
The sky appears blue because molecules in the atmosphere scatter blue light from the sun more than other colours. Since blue light is scattered in all directions, it reaches our eyes from every part of the sky, making it appear blue.

24. What is total internal reflection?
Total internal reflection is the phenomenon where light, passing through a denser medium like water or glass, hits the boundary with a less dense medium like air at an angle and reflects entirely into the denser medium instead of refracting out.

25. How does a periscope work?
A periscope uses two mirrors placed at 45-degree angles to each other. Light from an object hits the top mirror, reflects down to the lower mirror, and then to the viewer’s eye, allowing the person to see objects that are above or around obstacles.

5 Important Topics of Class 7 Science Chapter 11 You Shouldn’t Miss!

Benefits of Class 7 Chapter 11 Science Important Questions

• Simplifies Light Concepts - Important questions clarify core ideas like light’s path, reflection, and refraction, making these easier to understand.

• Strengthens Image Formation Skills - Practising with mirrors and lenses helps students see how different types form images, a key part of the chapter.

• Connects to Natural Phenomena - Questions on light dispersion allow students to link concepts to everyday examples like rainbows.

• Explains Vision Basics - Questions about the human eye help students learn how we see and cover essential vision topics.

• Ideal for Quick Revision - These questions summarise main points, making them useful for efficient review before exams.

Conclusion

Important Questions for Chapter 11 - Light in Class 7 Science helps students understand how light works, interacts with mirrors and lenses and enables us to see. By learning about reflection, refraction, and dispersion, students see how light affects things around us and learn about common effects like rainbows and mirrors. This chapter encourages curiosity about the natural world and lays the foundation for more learning about light in future classes.

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