- Define and explain Changing Shadows in your own words
- Use key terms such as shadow accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on Changing Shadows: investigating how moving a light or object makes shadows grow, shrink and move.
Investigating how moving a light or object makes shadows grow, shrink and move.
Key ideas
Moving the light or object changes the shadow
Hold a puppet close to a lamp and its shadow on the wall is huge; move it away and the shadow shrinks. Bringing the object nearer the light blocks a wider spread of rays, so the shadow grows. This is how shadow puppet shows make giant characters from small hands.
Light travels in straight lines
Light cannot bend around corners — it always moves in straight lines called rays. That is why you cannot see around a wall but you can see down a straight corridor. Shadows have sharp edges because light cannot curve around the object making them.
Key term — shadow: The dark shape formed when an object blocks light from reaching a surface.
A torch shines at a wooden block standing on a table. Where will the shadow appear, and what happens if the torch is moved closer to the block?
The block is opaque, so it blocks the torch's straight-travelling rays. The shadow forms on the table and wall on the far side from the torch. Moving the torch closer means the block blocks a wider spread of rays. The shadow grows larger.
Answer: The shadow appears on the opposite side from the torch, and moving the torch closer makes the shadow bigger.
- Believing light bends around objects Light travels in straight lines, which is exactly why shadows exist.
- Thinking shadows can appear on the same side as the light A shadow always falls opposite the light source, where the light is blocked.
Practice
Glass is transparent, so light passes straight through instead of being blocked.
The shadow gets smaller, because the toy blocks a narrower spread of rays.
At midday the Sun is high overhead so light comes almost straight down; in the evening the Sun is low, so your body blocks rays at a shallow angle and the shadow stretches out.
The Sun and stars (also acceptable: lightning, fireflies, glow-worms).
Quick check
Which of these best defines "shadow"?
Why can't you see someone standing around a corner?
Is a mirror a light source? Explain.
- Changing Shadows: investigating how moving a light or object makes shadows grow, shrink and move.
- Moving the light or object changes the shadow: Hold a puppet close to a lamp and its shadow on the wall is huge; move it away and the shadow shrinks.
- opaque: A material that light cannot pass through, so it makes a clear dark shadow.
- Watch out for: believing light bends around objects