E X E R C I S E S CHAPTER 9 Light – Reflection and Refraction SCIENCE NCERT TEXTBOOK (CBSE) CLASS 10:

 E X E R C I S E S  

CHAPTER  9  Light – Reflection and  Refraction


1. Which one of the following materials cannot be used to make a lens?

  • Answer: (d) Clay
    • Explanation: Lenses are typically made from materials like glass or plastic, which have optical properties that can bend light. Clay, on the other hand, does not have these properties and is not suitable for lens-making.

2. The image formed by a concave mirror is observed to be virtual, erect, and larger than the object. Where should the position of the object be?

  • Answer: (d) Between the pole of the mirror and its principal focus.
    • Explanation: In a concave mirror, if the object is placed between the pole and the focus (closer to the mirror than the focal point), the image formed will be virtual, erect, and magnified.

3. Where should an object be placed in front of a convex lens to get a real image of the size of the object?

  • Answer: (a) Between the optical centre of the lens and its principal focus.
    • Explanation: To form a real image of the same size as the object using a convex lens, the object should be placed at twice the focal length (2F), which is between the optical center and the focus.

4. A spherical mirror and a thin spherical lens have each a focal length of –15 cm. The mirror and the lens are likely to be:

  • Answer: (a) Both concave.
    • Explanation: A negative focal length indicates that both the spherical mirror (concave) and the spherical lens (concave lens) are diverging. Concave mirrors and concave lenses both have negative focal lengths.

5. No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be:

  • Answer: (d) Either plane or convex.
    • Explanation: A plane mirror always forms an erect, virtual image. A convex mirror also forms an erect, virtual image regardless of the object’s position.

6. Which of the following lenses would you prefer to use while reading small letters found in a dictionary?

  • Answer: (c) A convex lens of focal length 5 cm.
    • Explanation: A convex lens with a short focal length (5 cm) is suitable for reading small letters because it has a stronger converging power, making it ideal for near objects like a dictionary.

7. We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this case.

  • Answer: The object should be placed between the pole and the focal point of the concave mirror (less than 15 cm). The image formed will be virtual, erect, and magnified.

  • Ray Diagram:

    • The ray diagram for this case shows the object placed closer than the focal point of the concave mirror, resulting in a magnified, erect, and virtual image.

8. Name the type of mirror used in the following situations:

  • (a) Headlights of a car: Concave mirror (Focuses light to a single point for better illumination.)
  • (b) Side/rear-view mirror of a vehicle: Convex mirror (Forms a smaller, erect image and provides a wide field of view.)
  • (c) Solar furnace: Concave mirror (Concentrates sunlight to a focal point to generate heat.)

9. One-half of a convex lens is covered with black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.

  • Answer: Yes, the convex lens will still produce a complete image. When half of a convex lens is covered, the remaining half can still bend light to form a complete image, though the intensity of the image will be reduced. The image will still be formed as the entire lens is not needed to form the image.

10. An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size, and nature of the image formed.

  • Answer:
    • Ray Diagram:
      • Object placed at 25 cm and focal length is 10 cm.
      • Using the lens formula: 1f=1v−1u\frac{1}{f} = \frac{1}{v} - \frac{1}{u} 110=1v−1−25\frac{1}{10} = \frac{1}{v} - \frac{1}{-25}Solving gives v=16.67cm.
    • Nature of the image: Real, inverted, and reduced in size.
    • Size of the image: Use magnification formula m=vu×object sizem = \frac{v}{u} \times \text{object size}.

11. A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.

  • Answer:
    • Using the lens formula: 1f=1v−1u\frac{1}{f} = \frac{1}{v} - \frac{1}{u} 1−15=110−1u\frac{1}{-15} = \frac{1}{10} - \frac{1}{u} Solving gives u=−30u = -30cm (object is placed 30 cm from the lens).
    • Ray Diagram: The image will be virtual, upright, and diminished.

12. An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.

  • Answer:
    • Using the lens formula: 1f=1v−1u\frac{1}{f} = \frac{1}{v} - \frac{1}{u} 115=1v−1−10\frac{1}{15} = \frac{1}{v} - \frac{1}{-10} Solving gives v=−6 (virtual image).
    • Nature of image: Virtual, erect, and diminished.

13. The magnification produced by a plane mirror is +1. What does this mean?

  • Answer: A magnification of +1 means that the image is the same size as the object and it is upright (virtual image) in a plane mirror.

14. An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position of the image, its nature, and size.

  • Answer:
    • Focal length f=R2=15cm.
    • Using the lens formula: 1f=1v−1u\frac{1}{f} = \frac{1}{v} - \frac{1}{u} 115=1v−1−20\frac{1}{15} = \frac{1}{v} - \frac{1}{-20} Solving gives v=−12v = -12 cm (virtual, diminished).
    • Nature: Virtual, erect, and diminished.

15. An object of size 7.0 cm is placed at 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed, so that a sharp focused image can be obtained? Find the size and the nature of the image.

  • Answer:
    • Using the lens formula: 1f=1v−1u\frac{1}{f} = \frac{1}{v} - \frac{1}{u} 1−18=1v−1−27\frac{1}{-18} = \frac{1}{v} - \frac{1}{-27}Solving gives v=54v = 54 cm (real and inverted).
    • Size of the image: Use magnification formula to calculate the size.

16. Find the focal length of a lens of power –2.0 D. What type of lens is this?

  • Answer:
    • Focal length f=1P=1−2.0=−50f = \frac{1}{P} = \frac{1}{-2.0} = -50cm.
    • Type of lens: Diverging lens (concave lens).

17. A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?

  • Answer:
    • Focal length f=1P=11.5=66.67f = \frac{1}{P} = \frac{1}{1.5} = 66.67cm.
    • Type of lens: Converging lens (convex lens).

Comments

Post a Comment

Popular posts from this blog

NOTES Chapter 15: Our Environment Class 10 Science – CBSE NCERT

  Chapter 15: Our Environment Class 10 Science – CBSE NCERT Chapter 15 focuses on the various components that make up our environment, including ecosystems , biotic and abiotic factors , and food chains and webs . It highlights the balance of nature , biodiversity , and environmental issues like pollution, deforestation, and the need for sustainable development. The chapter also explains the impact of human activities on the environment and emphasizes the importance of conserving natural resources for future generations. 1. The Environment and Its Components The environment is the surrounding in which organisms live. It includes both living and non-living things and can be broadly classified into two categories: 1.1 Biotic Components : These are the living organisms in the environment. They include: Plants (producers), Animals (consumers), Microorganisms (decomposers). 1.2 Abiotic Components : These are the non-living factors that affect the living organisms in th...
Read more

NOTES Chapter 12: "Sound" from Class 9 Science CBSE NCERT:

  summary of Chapter 12: "Sound" from Class 9 Science CBSE NCERT : 1. What is Sound? Sound is a form of energy that is produced by the vibration of objects and propagates through a medium (solid, liquid, or gas) in the form of waves. Sound travels in waves and can be heard when it reaches our ears . How is sound produced? Sound is produced when an object vibrates. These vibrations cause the particles of the medium to move, creating compressions and rarefactions (regions of high and low pressure) that travel through the medium. 2. Propagation of Sound Sound needs a medium (like air, water, or solid objects) to travel. It cannot travel in a vacuum. How sound waves travel : Sound waves are longitudinal waves (particles of the medium move in the same direction as the wave). When an object vibrates, it creates a series of compressions (regions where particles are close together) and rarefactions (regions where particles are spread apart) in the surrounding medium. These co...
Read more

Moments Chapter 3 of CBSE Class 9, titled "Iswaran the Storyteller" by R.K. Narayan:

  summary of Chapter 3 of Moments for CBSE Class 9, titled "Iswaran the Storyteller" by R.K. Narayan : Summary: In this chapter, the story is centered around Iswaran , a cook who works for the narrator, and his fascinating way of telling stories. Iswaran's storytelling skills and his adventurous nature provide both entertainment and a sense of mystery to the narrator, who works in a small town. The narrator begins by describing Iswaran as an enthusiastic and talented cook who makes delicious food and is always happy to serve. Iswaran is very devoted to his job and never seems to get tired, no matter how much work is piled up. He is also well known for his remarkable storytelling abilities. He often entertains the narrator with thrilling stories, which he describes in vivid detail. The Background of Iswaran’s Life: Iswaran is originally from a village, and he later moves to the town where he works for the narrator. He is described as a "man of strong character...
Read more