Chapter 11: Light – Shadows and Reflections

Introduction

Light is a form of energy that enables us to see objects. It travels in straight lines and interacts with objects to produce shadows, reflection, and images. Understanding light is essential for optics, daily life, and technology.

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1. Shadows

• Definition: A shadow is a dark area formed when an opaque object blocks light.
• Characteristics of shadows:
  • Formed when light is blocked
  • Size and shape change with distance from the light source and object
  • Can be partial or total
• Examples: Shadow of a tree, building, or hand

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2. Reflection of Light

• Definition: Reflection is the bouncing back of light from a surface.
• Laws of Reflection:
  1. Angle of incidence = Angle of reflection
  2. Incident ray, reflected ray, and normal lie in the same plane
• Types of reflection surfaces:
  • Plane mirror: Flat surface, produces virtual images
  • Spherical mirrors: Concave and convex, produce magnified or diminished images

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3. Image Formation by Mirrors

• Plane mirror: Upright, virtual, same size, laterally inverted
• Concave mirror: Converges light; can produce real or virtual images
• Convex mirror: Diverges light; produces virtual, diminished images

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4. Key Points to Remember

• Light travels in straight lines.
• Shadows form when light is blocked.
• Reflection obeys laws of reflection.
• Mirrors produce images that can be real or virtual depending on the type of mirror.

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Questions – Light: Shadows and Reflections

1. Very Short Answer (1 mark)

1. Define shadow.
2. Give one example of a shadow in daily life.
3. Define reflection.
4. Name the two laws of reflection.
5. Give one example of a plane mirror.
6. Name a concave mirror.
7. Name a convex mirror.
8. What is a virtual image?
9. What is a real image?
10. How does the size of a shadow change when the object moves closer to the light source?

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2. Multiple Choice Questions (MCQ)

1. Light travels in:
   a) Curved lines
   b) Straight lines
   c) Circles
   d) Zig-zag
2. Which mirror converges light?
   a) Plane
   b) Concave
   c) Convex
   d) None
3. Laws of reflection include:
   a) Angle of incidence = Angle of reflection
   b) Normal lies in a different plane
   c) Reflected ray bends randomly
   d) Light slows down
4. Image in a plane mirror is:
   a) Real and inverted
   b) Virtual and upright
   c) Magnified
   d) Real and magnified
5. Convex mirrors produce:
   a) Virtual and diminished images
   b) Real images
   c) Magnified images
   d) No image

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3. Fill in the Blanks

1. A shadow is formed when __________ light is blocked.
2. Angle of incidence is equal to __________.
3. Plane mirrors produce __________ images.
4. Concave mirrors __________ light.
5. Convex mirrors __________ light.

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4. True/False Type

1. Shadows can only form in the dark. (True/False)
2. Reflection occurs when light bounces back from a surface. (True/False)
3. Plane mirror images are laterally inverted. (True/False)
4. Convex mirrors converge light to a point. (True/False)
5. Laws of reflection apply to all types of mirrors. (True/False)

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5. Short Answer Questions (2–3 marks)

1. Explain how a shadow is formed with an example.
2. State the laws of reflection.
3. Describe the characteristics of an image formed by a plane mirror.
4. Give one difference between concave and convex mirrors.
5. Give two examples of reflection in daily life.

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6. Long Answer Questions (4–5 marks)

1. Explain the formation of shadows and factors affecting their size and shape.
2. Describe reflection of light and laws of reflection with a diagram.
3. Explain image formation by plane, concave, and convex mirrors.
4. Discuss the uses of concave and convex mirrors in daily life.
5. Explain why plane mirror images appear laterally inverted.

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7. Higher-Order Thinking (HOT) & Application

1. Why does a concave mirror produce a magnified image when an object is placed between the focus and the mirror?
2. Explain why convex mirrors are used as rear-view mirrors in vehicles.
3. How does distance from the light source affect the length of a shadow?

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8. Passage-Based Questions

Read the passage and answer:
Light travels in straight lines. When it is blocked, shadows form. Mirrors reflect light according to laws of reflection. Plane mirrors produce virtual, upright images. Concave mirrors converge light, while convex mirrors diverge light, producing diminished virtual images.

1. What happens when light is blocked?
2. Name the types of mirrors that converge and diverge light.
3. What type of image is formed by a plane mirror?
4. State one use of a convex mirror.

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Answer Key – Light: Shadows and Reflections

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1. Very Short Answer

1. Dark area formed when an opaque object blocks light
2. Shadow of a tree or building
3. Bouncing back of light from a surface
4. Angle of incidence = Angle of reflection; Incident ray, reflected ray, and normal lie in the same plane
5. Mirror in a bathroom
6. Makeup mirror, shaving mirror
7. Rear-view mirror in vehicles
8. Image that cannot be projected on a screen
9. Image that can be projected on a screen
10. It becomes larger

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2. MCQ Answers

1. b) Straight lines
2. b) Concave
3. a) Angle of incidence = Angle of reflection
4. b) Virtual and upright
5. a) Virtual and diminished images

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3. Fill in the Blanks

1. opaque
2. angle of reflection
3. virtual
4. converges
5. diverges

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4. True/False

1. False
2. True
3. True
4. False
5. True

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5. Short Answer

1. Shadow forms when light is blocked by an opaque object; e.g., shadow of a hand
2. Laws: Angle of incidence = Angle of reflection; Incident, reflected ray, and normal lie in the same plane
3. Upright, virtual, same size, laterally inverted
4. Concave – converges light; Convex – diverges light
5. Reflection from mirrors, rear-view mirrors, shaving mirrors

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6. Long Answer

1. Shadow size depends on distance from light and object; closer light → larger shadow
2. Reflection: Incident ray strikes surface → bounces back; laws explained with diagram
3. Plane – virtual upright; Concave – magnified/diminished, real/virtual; Convex – virtual, diminished
4. Concave – shaving mirrors, torches; Convex – rear-view mirrors, security mirrors
5. Lateral inversion occurs due to reflection angles

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7. HOT & Application

1. Object within focus → reflected rays diverge → magnified virtual image
2. Convex mirrors give wide field of view → safer for driving
3. Closer object to light → shadow larger; farther → shadow smaller

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8. Passage-Based

1. A shadow forms
2. Concave – converges; Convex – diverges
3. Virtual and upright
4. Rear-view mirror in vehicles