Class 6 Science Notes Chapter 11 (Light; Shadows and Reflections) – Science Book

Detailed Notes with MCQs of Chapter 11: Light, Shadows and Reflections. This is an important chapter, not just for your class but also as a foundation for concepts tested in various government exams. Pay close attention to the details.

Chapter 11: Light, Shadows and Reflections - Detailed Notes

1. What is Light?

• Light is a form of energy that enables us to see objects around us.
• We see objects when light coming from the object (either emitted by it or reflected from it) enters our eyes.

2. Sources of Light:

• Luminous Objects: Objects that emit or give out their own light.
  • Examples: Sun, stars, electric bulb (when switched on), torch, candle flame, firefly.
• Non-Luminous Objects: Objects that do not emit their own light. We see them because they reflect light falling on them from luminous sources.
  • Examples: Moon (reflects sunlight), planets, chair, table, book, trees, humans.

3. How Light Travels:

• Light travels in straight lines. This property is called the rectilinear propagation of light.
• Evidence: Formation of shadows, image formation in a pinhole camera, beams of light from a projector or lighthouse.

4. Classification of Objects based on Interaction with Light:

• Transparent Objects: Allow light to pass through them completely. We can see clearly through them.
  • Examples: Clear glass, clean water, air, cellophane paper (clear).
• Translucent Objects: Allow light to pass through them partially. We cannot see clearly through them; objects appear blurry.
  • Examples: Frosted glass, butter paper, tracing paper, thin plastic sheet, muddy water.
• Opaque Objects: Do not allow any light to pass through them. We cannot see through them at all.
  • Examples: Wood, metal sheet, brick wall, thick cardboard, book, stone.

5. Shadows:

• What is a Shadow? A shadow is a dark region formed behind an opaque object when it blocks the path of light.
• Conditions necessary for shadow formation:
  1. A source of light.
  2. An opaque object to obstruct the light.
  3. A screen or surface behind the object where the shadow can be formed.
• Properties of Shadows:
  • Shadows are always formed on the opposite side of the opaque object from the source of light.
  • The shape of the shadow roughly resembles the shape (outline) of the opaque object, but it can be distorted depending on the angle of light and the surface.
  • The size of the shadow depends on:
    • The distance between the light source and the object (closer the source, larger the shadow).
    • The distance between the object and the screen (closer the object to the screen, smaller and sharper the shadow; farther the object from the screen, larger and fuzzier the shadow).
  • Shadows are always dark, regardless of the colour of the opaque object. They only show the outline, not the details or colour of the object.
  • Shadows require a screen (ground, wall, paper) to be formed. No shadow is formed in empty space.

6. Pinhole Camera:

• Principle: Based on the rectilinear propagation of light (light travels in straight lines).
• Construction: A simple light-proof box with a tiny hole (pinhole) on one side and a translucent screen (like tracing paper) on the opposite side.
• Image Formation:
  • Light rays from different points on an object travel in straight lines through the pinhole and form an image on the screen.
  • The image formed is inverted (upside down) and usually smaller than the object.
  • Light rays from the top of the object pass through the pinhole and strike the bottom of the screen.
  • Light rays from the bottom of the object pass through the pinhole and strike the top of the screen.
  • The image can be colourful if the object is colourful.
  • Uses: Can be used to safely view bright objects like the Sun (during an eclipse, for example, by projecting the image).

7. Mirrors and Reflection:

• Reflection: The bouncing back of light rays when they strike a surface.
• Mirror: A smooth, highly polished surface (like glass coated with a reflective material) that reflects most of the light falling on it. Plane mirrors are flat mirrors.
• Image Formation by a Plane Mirror:
  • When you look into a plane mirror, you see an image of yourself or objects.
  • The image formed is virtual (cannot be obtained on a screen).
  • The image is erect (upright, same way up as the object).
  • The image is the same size as the object.
  • The image is formed behind the mirror at the same distance as the object is in front of it.
  • The image shows lateral inversion. This means the left side of the object appears as the right side of the image, and vice versa. (Example: The word AMBULANCE is written in reverse on the front of ambulance vehicles so that drivers ahead can read it correctly in their rearview mirrors).

Key Takeaways for Exams:

• Understand the difference between luminous and non-luminous objects with examples.
• Know the definitions and examples of transparent, translucent, and opaque materials.
• Remember the conditions required for shadow formation and the key properties of shadows (shape, size dependence, colour).
• Understand the principle of a pinhole camera and the characteristics of the image formed (inverted, real, can be smaller/larger depending on distances, can be colourful).
• Define reflection.
• Memorize the characteristics of the image formed by a plane mirror (virtual, erect, same size, same distance, laterally inverted). Be very clear about lateral inversion.

Multiple Choice Questions (MCQs)

Here are 10 questions to test your understanding. Choose the best answer.

1. Which of the following is a luminous object?
   (a) Moon
   (b) Earth
   (c) A burning candle
   (d) A mirror

2. An object that allows light to pass through it completely is called:
   (a) Opaque
   (b) Translucent
   (c) Transparent
   (d) Luminous

3. Shadows are formed because:
   (a) Light travels in curved lines.
   (b) Opaque objects reflect light.
   (c) Light travels in straight lines and opaque objects block it.
   (d) Transparent objects absorb light.

4. Which of these is required to form a shadow?
   (a) A source of light only
   (b) An opaque object only
   (c) A screen only
   (d) A source of light, an opaque object, and a screen

5. The image formed by a pinhole camera is generally:
   (a) Erect and larger
   (b) Inverted and smaller
   (c) Erect and same size
   (d) Inverted and virtual

6. Butter paper is an example of a:
   (a) Transparent object
   (b) Translucent object
   (c) Opaque object
   (d) Luminous object

7. The phenomenon where the left side appears right and the right side appears left in a plane mirror image is called:
   (a) Reflection
   (b) Rectilinear propagation
   (c) Lateral inversion
   (d) Shadow formation

8. Which statement is TRUE about the image formed by a plane mirror?
   (a) It is real and inverted.
   (b) It is virtual and smaller than the object.
   (c) It is virtual, erect, and the same size as the object.
   (d) It is real, erect, and larger than the object.

9. If you stand 2 meters in front of a plane mirror, how far behind the mirror does your image appear to be?
   (a) 1 meter
   (b) 2 meters
   (c) 4 meters
   (d) 0 meters

10. A shadow's colour is always:
    (a) The same colour as the object
    (b) Black or dark grey
    (c) White
    (d) Dependent on the colour of the light source

Answer Key for MCQs:

1. (c) A burning candle
2. (c) Transparent
3. (c) Light travels in straight lines and opaque objects block it.
4. (d) A source of light, an opaque object, and a screen
5. (b) Inverted and smaller (Note: Size depends on distances, but typically smaller in simple setups. The key feature is inversion).
6. (b) Translucent object
7. (c) Lateral inversion
8. (c) It is virtual, erect, and the same size as the object.
9. (b) 2 meters
10. (b) Black or dark grey

Revise these notes thoroughly. Understanding these fundamental concepts of light is crucial. Let me know if any part needs further clarification.