Key Concepts| Class 6 science Ch Light, Shadow and Reflection(Oxford Book)

  1. Light:
    • Light is a form of energy that helps us see objects.
    • Luminous objects produce their own light (e.g., the Sun, stars, candle).
    • Non-luminous objects do not produce light (e.g., table, book).
  2. Shadows:
    • Shadows are formed when an opaque object blocks the path of light.
    • The shadow of an object shows its outline or shape, not its color.
    • A shadow can be sharp or blurry depending on the light source and the object’s distance from the surface.
  3. Reflection:
    • Reflection occurs when light bounces off a surface.
    • A regular surface (like a mirror) produces a clear reflected image.
    • A rough surface causes diffused reflection, where the reflected rays scatter, making the image unclear.
  4. Pinhole Camera:
    • A pinhole camera uses a small hole to project an inverted image of an object onto a screen.
    • The image formed is inverted and reversed.
  5. Transparent, Translucent, and Opaque Materials:
    • Transparent materials allow all light to pass through (e.g., glass, air).
    • Translucent materials allow only some light to pass through (e.g., butter paper).
    • Opaque materials do not allow light to pass through (e.g., wood, metal).

Important Points:

  • Light travels in a straight line and forms shadows when blocked by an opaque object.
  • Reflection of light helps us see images in mirrors and smooth surfaces.
  • The size and clarity of shadows depend on the distance between the object and the screen, and the size of the light source.

Types of Reflection:

  • Regular Reflection: Light reflects in parallel rays, forming a clear image (e.g., mirror).
  • Diffused Reflection: Light scatters in different directions, forming unclear or no image (e.g., rough walls).

This is a concise summary of the key concepts in the chapter on Light, Shadow, and Reflection. Let me know if you need further details!

Ch Light, Shadow and Reflection

Page 175| Exercises

I. Objective type questions

  1. Choose the correct option

1. Light enable us to

a. hear               b. see

c.taste               d. None of the above

2. Which of these is not a natural source of light?

a. A star                b. Firefly

c. Tubelight         d. The sun

3. Pick out the opaque material from the following.

a. Grass                                                b. Air

c. Clear glass                       d. Clean water

4. Which of these is not necessary to form a shadow?

a. The sun                           b. A source of light

c. An opaque object       d. A screen or surface

5. A pinhole camera produces which of the following?

  1. Coloured inverted image
  2. Black and white inverted image
  3. Black and white upright image
  4. Coloured upright image

6. Which of these is not a source of light?

a. A star                                c. A lit candle

b. A lit light bulb                d. A book

7. Which of these is transparent?

a. Butter paper                                 b. Pure air

c. Mud                                  d. A mirror

8. What happens when we look at an object through a translucent material?

a. We can see it very clearly.

b. Can not see it at all.

c. We can see it, but not very clearly.

d. We can see its image.

9. The shadow of an object shows its

a. size                                    b. colour

c. shape or outline           d. all of these

10. Unlike its shadow, the image of an object shows its.

a, outline                             b. shape

d. none of these              c. colour

Objective Type Questions

A. Choose the correct option

  1. Light enables us to
    b. see
  2. Which of these is not a natural source of light?
    c. Tubelight
  3. Pick out the opaque material from the following.
    a. Grass
  4. Which of these is not necessary to form a shadow?
    a. The sun
  5. A pinhole camera produces which of the following?
    b. Black and white inverted image
  6. Which of these is not a source of light?
    d. A book
  7. Which of these is transparent?
    b. Pure air
  8. What happens when we look at an object through a translucent material?
    c. We can see it, but not very clearly.
  9. The shadow of an object shows its
    c. shape or outline
  10. Unlike its shadow, the image of an object shows its
    c. colour

B. Write T for the true statement and F for the false one. Correct the false statement(s).

1. We cannot see an object through a transparent material.

2. Clear air is opaque.

3. Shadows cannot be formed without a source of light.

4. The shadow of an object shows its colour.

5. The image formed by a pinhole camera is coloured.

B. Write T for the true statement and F for the false one. Correct the false statement(s).

  1. We cannot see an object through a transparent material.
    F – Correction: We can see through a transparent material.
  2. Clear air is opaque.
    F – Correction: Clear air is transparent.
  3. Shadows cannot be formed without a source of light.
    T
  4. The shadow of an object shows its colour.
    F – Correction: The shadow of an object shows its shape or outline, not its colour.
  5. The image formed by a pinhole camera is coloured.
    F – Correction: The image formed by a pinhole camera is black and white.

II. Very short answer type questions.

A. Give two examples of the following.

1. Human-made sources of light

2. Opaque materials

3. Objects that can form a shadow

4. Irregular surfaces (with respect to reflection)

5. Regular surfaces (with respect to reflection)

Ans:

1.Human-made sources of light:

Electric bulb and Candle

2.Opaque materials:

Wood and Metal

3.Objects that can form a shadow:

A chair and A book

iv.Irregular surfaces (with respect to reflection):

Rough wall and Wooden surface

v. Regular surfaces (with respect to reflection):

Mirror and Still water

B. Define the following terms.

1. A natural source of light

2. Transparent material

3. Translucent material

4. Opaque material

5. Shadow

6. Diffused reflection

Ans:

  1. A natural source of light:
    A natural source of light is something that produces its own light naturally, without the need for an external power source. Example: The sun.
  2. Transparent material:
    A transparent material allows light to pass through it so that objects behind can be clearly seen. Example: Glass.
  3. Translucent material:
    A translucent material allows some light to pass through but scatters it, making objects on the other side appear blurry. Example: Butter paper.
  4. Shadow:
    A shadow is a dark area created when an opaque object blocks light from a light source.
  5. Diffused reflection:
    Diffused reflection occurs when light strikes a rough surface, and the reflected rays scatter in many directions, leading to a blurry or diffused image.

Opaque material:
An opaque material does not allow light to pass through it, and as a result, objects behind it cannot be seen. Example: Wood

III. Short answer type questions.

1. Classify the following as ‘luminous’ and ‘non-luminous’:

A table, a cup, a star in the night sky, candle flame, a cupboard, a book, water

Ans:

Non-luminous: A table, a cup, a cupboard, a book, water

Luminous: A star in the night sky, candle flame

2. What are natural sources of light? Give two examples.

Ans:Natural sources of light are those that produce light naturally.

Example 2: A star

Example 1: The Sun

3. If you want a wall, so that you can see clearly on the other side, what kind of material would you use to build it?

Ans: To see clearly through the wall, the material should be transparent, such as glass.

4. What property of light is demonstrated by formation of shadows and pinhole camera?

Ans: The rectilinear propagation of light is demonstrated by the formation of shadows and images in a pinhole camera.

5. Write down any two characteristics of a shadow.

  • A shadow is always formed in the opposite direction of the light source.
  • The size of a shadow depends on the distance between the light source and the object.

IV. Long answer type questions.

1. Can you see clearly through a transparent material? Give two examples of transparent materials. Describe an activity to determine whether a given material is transparent or not.

Yes, you can see clearly through a transparent material because it allows light to pass through it without scattering, making objects on the other side visible.

Examples of Transparent Materials:

  1. Glass
  2. Water

Activity to Determine if a Material is Transparent:

Objective: To check if a material is transparent.

Materials Required:

  • A piece of paper with a simple drawing (like a letter “A”)
  • A transparent material (like a glass sheet)
  • An opaque material (like a book or cardboard)

Procedure:

  1. Place the paper with the drawing (the letter “A”) on a table.
  2. Hold the transparent material (glass sheet) above the paper.
  3. If you can clearly see the drawing of the letter “A” through the glass, it means the material is transparent.
  4. Repeat the same procedure with an opaque material like a book or cardboard. If you cannot see the drawing through the material, then it is opaque.

Conclusion: If you can see through the material and clearly view the object on the other side, the material is transparent. If the material blocks the view, it is opaque.

This simple activity helps determine whether a material is transparent, allowing light to pass through and making objects visible behind it.

2. Why is it that we cannot see a reflected image on a rough wall?

Ans: We cannot see a reflected image on a rough wall because of diffused reflection.

Explanation: When light strikes a smooth surface, such as a mirror, it reflects at a uniform angle, and the rays remain parallel. This produces a clear, distinct image because all the reflected light rays follow the same path.

However, when light hits a rough surface, like a rough wall, the surface does not reflect the light uniformly. Instead, the light rays are scattered in many different directions. This scattering of light is called diffuse reflection.

Since the reflected rays are scattered in various directions, they do not come together to form a clear, focused image. Instead, the reflected light is spread out, and we cannot see a sharp or distinct image as we would on a smooth surface.

Conclusion: A rough surface scatters the reflected light in many directions, preventing the formation of a clear, reflected image, unlike a smooth surface like a mirror that reflects light uniformly to form an image.

3. Draw a diagram to illustrate reflection of a parallel beam of light from a smooth surface.

Diagram:

image 22
Class 6 science Ch Light, Shadow and Reflection(Oxford Book) 3

4. Draw a diagram to show how an image is formed in a pinhole camera. Label all the parts of the pinhole camera.

Ans:

image 21
Class 6 science Ch Light, Shadow and Reflection(Oxford Book) 4

Labels:

  • Object: The object outside the pinhole camera.
  • Camera Box: The outer casing of the camera.
  • Pinhole: The small hole that allows light to enter the camera.
  • Screen: The surface where the inverted image is formed.
  • Light Rays: Straight lines of light passing through the pinhole to form the image.

Conclusion: The pinhole camera forms an inverted and reversed image of the object on the screen inside. The image quality can be affected by the size of the pinhole and the distance between the pinhole and the screen.

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