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Grade 5 (age 10-11)

grade 5 Light and Lenses

Light and Lenses

Light travels straight, so a blocked object casts a shadow, and a smooth mirror bounces the light back. The angle in (angle of incidence) always equals the angle out (angle of reflection). Light also bends when it passes from air into water or glass, which is why a straw in a cup looks broken; this is refraction. Change the angle of incidence and the reflection shows itself; move the object and the convex lens and the rays gather into an image.

How Does Light Travel?

45°
💡 Properties of Light
①Light travels in straight lines — that creates shadows
②Light reflects off mirrors
③Angle of incidence = angle of reflection (always equal!)
④We see objects because light reflects into our eyes

What Do Lenses Do?

120
🔍 Convex vs Concave Lens
①Convex lens: thicker in the middle — focuses light
②Magnifier, camera, eye lens are convex!
③Concave lens: thinner in the middle — spreads light
④Glasses for nearsightedness use concave lenses

What is Refraction?

Refraction of Light
Light bends when entering a different material (refraction)
Why a coin in water looks closer!
🌊 Refraction in Daily Life
①A straw in a cup looks bent
②Pool bottom looks shallower than it is
③Rainbow: refraction + reflection in raindrops
④Prism: white light → seven rainbow colors!

Summary

Light & Lens Core
Straight + Reflect + Refract = 3 properties of light
Lenses use refraction to focus or spread light
🎯 Key Points
①Light goes straight → makes shadows
②Light reflects → incidence = reflection
③Light refracts → bends in different materials
④Convex lens: focuses light (magnifier, camera)
⑤Concave lens: spreads light (glasses for nearsightedness)

Examples and Unit Test

Example 1
Light hits a mirror at an angle of incidence of 30 degrees. What is the angle of reflection?
1
When light hits a mirror it reflects, and the angle of incidence always equals the angle of reflection.
2
Since the angle of incidence is 30 degrees, the angle of reflection is also 30 degrees.
▸ Angle of reflection = 30 degrees
In reflection, the angle of incidence always equals the angle of reflection.
Example 2
Why can a magnifying glass make small letters look bigger?
1
A magnifying glass is a convex lens, thicker in the middle.
2
A convex lens focuses light, making the letters look larger (magnified).
▸ A magnifier is a convex lens, so it focuses light and enlarges the letters
A convex lens focuses light, while a concave lens spreads it.
Unit-test style
Which statement about light and lenses is correct?
①Light always travels along curved paths
②When light reflects off a mirror, incidence equals reflection
③A convex lens spreads light out
④A concave lens focuses light
⑤A straw in water looks straight because of refraction
▸ ② When light reflects off a mirror, incidence equals reflection
1
In reflection, the angle of incidence always equals the angle of reflection.
2
Light travels straight (①), a convex lens focuses light (③), a concave lens spreads it (④), and refraction makes the straw look bent (⑤).
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