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Study notes

Light & Shadows

Light is a form of energy that travels in straight lines and allows us to see the world around us.

Learn it step by step

Sources of Light

A light source is an object that gives off its own light, such as the Sun, a lit candle, or a lamp. The Moon and mirrors are not light sources because they only reflect light from other sources.

How Light Travels and How We See

Light always travels in straight lines. We see an object when light from a light source bounces off the object and enters our eyes.

Materials and Light

Different materials allow different amounts of light to pass through them.

Type of MaterialAmount of Light Passing ThroughExamples
TransparentAllows most light to pass throughClear glass, clear plastic sheet
TranslucentAllows some light to pass throughFrosted glass, tracing paper
OpaqueDoes not allow any light to pass throughCardboard, wood, metal
Comparison of transparent, translucent, and opaque materials

Formation of Shadows

A shadow forms when light travelling in straight lines is blocked by an opaque or translucent object. The shadow always appears on the side opposite to the light source.

Changing Shadow Sizes

A shadow becomes bigger when the object is moved closer to the light source, or when the screen is moved further away from the object. Moving the object further from the light source makes its shadow smaller.

Worked examples

Meiling placed a wooden toy between a torch and a wall. Explain how the shadow of the toy is formed on the wall.
  1. State the property of light: Light travels in straight lines.
  2. State the property of the object: The wooden toy is an opaque object.
  3. Explain how the shadow is cast: The wooden toy blocks the light travelling from the torch, forming a dark area called a shadow on the wall behind it.
Why is the Moon not considered a source of light, even though it looks bright at night?
  1. Define a light source: A light source must produce and give off its own light.
  2. Explain what happens with the Moon: The Moon does not produce its own light.
  3. Conclude clearly: The Moon only reflects light from the Sun into our eyes, so it is not a light source.
A student wants to make the shadow of an apple on a screen larger. Name two different ways to do this without changing the position of the screen.
  1. Recall the factor involving the light source and the object: Moving the light source closer to the object makes the shadow bigger.
  2. Method 1: Move the torch closer to the apple.
  3. Method 2: Move the apple closer to the torch (which also moves it further from the screen).
Bala looks at a book in a completely dark room with no light sources. Can he see the book? Explain your answer.
  1. State the direct answer: No, Bala cannot see the book.
  2. Explain the science rule for sight: We can only see an object when light bounces off it into our eyes.
  3. Connect to the question context: In a completely dark room, there is no light source to give off light, so no light can bounce off the book into Bala's eyes.

Mind map

Mind map for Light.

  • Light Sources
    • Give off own light (Sun, lamp)
    • Non-sources reflect light (Moon, mirror)
  • How Light Moves
    • Travels in straight lines
    • Reflects off surfaces into our eyes
  • Types of Materials
    • Transparent (allows most light)
    • Translucent (allows some light)
    • Opaque (blocks all light)
  • Shadows
    • Formed when light is blocked
    • Bigger when object is near torch
    • Smaller when object is far from torch
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