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3. Light Waves Light Travels in Straight Lines Speed of Light (Qualitative) Luminous and Non-luminous Objects Reflection of Light Ray Diagrams and Mirrors Refraction of Light Absorption, Transmission, and Scattering Dispersion of White Light Colours and Prisms
Year 8 • Physics
Light Waves
This lesson explores how light travels, how we see objects, how mirrors and prisms work, and why colours appear in nature — connecting physics concepts to real-life experiences to spark curiosity.
Lesson Objectives
- Understand light as a wave that travels in straight lines.
- Explain luminous and non-luminous objects.
- Describe reflection, refraction, and absorption of light.
- Use ray diagrams to explain mirrors.
- Understand dispersion and colours of white light.
1. Light Travels in Straight Lines
Light travels in straight lines. This is why shadows are formed and why we cannot see around corners.
Real-life curiosity:
If light could bend around objects, shadows would not exist. The sharp edges of shadows prove that light travels straight.
If light could bend around objects, shadows would not exist. The sharp edges of shadows prove that light travels straight.
Examples:
• Shadows of buildings in sunlight
• Torch beams in fog
• Laser pointers forming straight paths
2. Speed of Light (Qualitative)
Light travels extremely fast — much faster than sound.
Mind-blowing fact:
Light from the Sun takes about 8 minutes to reach Earth.
Light from the Sun takes about 8 minutes to reach Earth.
Curiosity moment:
When you see lightning before hearing thunder, it proves light travels faster than sound.
3. Luminous and Non-Luminous Objects
Luminous objects produce their own light.
Non-luminous objects do not produce light — we see them because they reflect light.
Luminous: Sun, bulb, candle, fire
Non-luminous: Moon, book, chair, humans
Non-luminous: Moon, book, chair, humans
Curiosity:
The Moon looks bright, but it does not produce light — it reflects sunlight.
4. Reflection of Light & Mirrors
Reflection happens when light bounces off a surface.
Key Rule:
Angle of incidence = Angle of reflection
Angle of incidence = Angle of reflection
Curiosity:
Why do mirrors reverse left and right but not up and down?
(This leads students towards later ideas of image formation.)
5. Ray Diagrams and Plane Mirrors
Ray diagrams help us understand how images are formed.
Plane mirror image properties:
• Same size as object
• Upright
• Same distance behind mirror as object in front
• Same size as object
• Upright
• Same distance behind mirror as object in front
6. Refraction of Light
Refraction happens when light changes direction as it moves between different materials.
Examples:
• Straw looks bent in water
• Swimming pools look shallower
• Lenses focus light
• Straw looks bent in water
• Swimming pools look shallower
• Lenses focus light
7. Absorption, Transmission & Scattering
Light can be absorbed, transmitted, or scattered.
• Absorption: Dark clothes absorb heat
• Transmission: Glass lets light pass
• Scattering: Sky appears blue
• Transmission: Glass lets light pass
• Scattering: Sky appears blue
Curiosity:
The sky is blue because blue light is scattered more than red light.
8. Dispersion of White Light
White light is made of many colours.
A prism splits white light into colours:
Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROYGBIV)
Red, Orange, Yellow, Green, Blue, Indigo, Violet (ROYGBIV)
Real-life wonder:
Rainbows form due to dispersion of sunlight by raindrops.
Practice Questions
A. Fill in the Blanks
- Light travels in __________ lines.
- The Sun is a __________ object.
- Reflection happens when light __________.
- A prism causes __________ of light.
- The sky looks blue due to __________.
B. True or False
- Light travels faster than sound.
- The Moon produces its own light.
- Refraction happens in mirrors.
- Glass transmits light.
- White light contains many colours.
C. Short Answer
- What is reflection?
- Why do shadows form?
- What is refraction?
- Name two luminous objects.
- Why does a straw look bent in water?
D. Curiosity Questions
- Why do we see lightning before thunder?
- Why are rainbows curved?
- Why do mirrors reverse left and right?
- Why are dark clothes hotter in sunlight?
- Why does fog make torch beams visible?
✅ Show Answer Key
A. Fill in the Blanks
- straight
- luminous
- bounces
- dispersion
- scattering
B. True or False
- True
- False
- False
- True
- True
C. Short Answer
- Reflection is the bouncing back of light.
- Because light travels in straight lines.
- Bending of light between materials.
- Sun, bulb.
- Because of refraction.
D. Curiosity Questions
- Light travels faster than sound.
- Because raindrops act like tiny prisms.
- Due to image formation rules of mirrors.
- They absorb more light energy.
- Light scatters off water droplets.
© Aviate Learning – Light Waves (Year 8)