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Grade 4 (age 9-10)

grade 4 Shadows and Mirrors

Shadows and Mirrors

Light travels in straight lines, so an opaque object casts a dark shadow behind it. The closer the light, the bigger the shadow; moving it away shrinks it again. A mirror bounces light back, and the angle in always matches the angle out: that is the law of reflection. Move the slider to change the light's place and angle, and the shadow grows while the rays bounce off the mirror.

Why do shadows form?

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🌗 For a shadow to form?
①There must be light
②An object must block the light
③Opaque objects cast a dark shadow; transparent ones cast a faint shadow
④Closer light → bigger shadow
⑤Farther light → smaller shadow

Mirrors bounce light

30
🪞 Mirror Reflection
①Light bounces off mirrors
②Incoming angle = outgoing angle
③This is the law of reflection
④You see your image because of reflection

Summary

Shadow Condition
Light + opaque object → Shadow
Blocking light creates a dark shadow behind
Law of Reflection
Incident angle = Reflection angle
Light bounces off a mirror at the same angle it arrives
🎯 Key Points
①Light travels in straight lines
②Shadows form behind opaque objects
③Closer light = bigger shadow
④Mirrors reflect at equal angles
⑤Transparent objects make faint shadows

Examples and Unit Test

Example 1
If you move a flashlight closer to an object, what happens to the size of the shadow?
1
A shadow forms behind an object when light is blocked by the opaque object.
2
The closer the light source is to the object, the larger the shadow becomes.
▸ The shadow becomes larger
A closer light source makes a larger shadow; a farther one makes it smaller.
Example 2
Light hits a mirror at a slant of 30 degrees. What is the angle of reflection?
1
When light hits a mirror, it bounces off at the same angle it came in (law of reflection).
2
Since the angle of incidence is 30 degrees, the angle of reflection is also 30 degrees.
▸ 30 degrees (incidence = reflection)
In a mirror reflection, the angle of incidence equals the angle of reflection.
Unit-test style
Which statement about shadows and mirrors is correct?
①Light curves as it travels, which makes shadows
②In a mirror, the angle of incidence equals the angle of reflection
③A shadow gets larger as the light source moves away
④Clear glass makes a dark shadow
⑤A mirror absorbs all the light
▸ ② In a mirror, the angle of incidence equals the angle of reflection
1
Light bounces off a mirror at the same angle it came in, so incidence equals reflection.
2
Light travels straight and makes shadows (①), a closer light source makes a larger shadow (③), clear objects let light through so their shadow is faint (④), and a mirror reflects light (⑤).
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