Light and Reflection
Discover how light travels, how we see objects, and what happens when light bounces off surfaces or bends through water.
How Light Travels
Light travels in straight lines called rays. It travels incredibly fast -- about 300,000 kilometres per second! That means light from the Sun reaches Earth in just over 8 minutes.
We can see objects because light bounces off them and enters our eyes. Without light, we cannot see anything -- that is why it is dark in a room with no light source.
Light Travels in Straight Lines
Light rays travel in straight lines from the source to our eyes
How Materials Interact with Light
Different materials let different amounts of light through. We classify them into three groups:
Transparent
Lets all light through. You can see clearly through it.
Examples: clear glass, clean water, air
Translucent
Lets some light through, but scatters it. You can see shapes but not clearly.
Examples: frosted glass, tissue paper, wax paper
Opaque
Lets no light through. You cannot see through it. Creates shadows.
Examples: wood, metal, cardboard, your body
Inquiry Question: Why do shadows form? Think about what happens when light hits an opaque object. What shape will the shadow be?
Reflection
Reflection happens when light bounces off a surface. Smooth, shiny surfaces (like mirrors, calm water, or polished metal) reflect light very well. This is why you can see your reflection in a mirror!
The Law of Reflection
Incoming ray
Normal line
Reflected ray
Key rule: The angle of incidence (incoming) equals the angle of reflection (bouncing off).
Think about it: Why can you see yourself in a calm lake but not in a choppy one? When the water surface is smooth, light reflects evenly. When it is rough, light scatters in many directions.
Refraction: Bending Light
Refraction happens when light passes from one material to another (like from air into water) and changes speed, causing it to bend.
Everyday Examples
- ●A straw in a glass of water looks bent or broken at the water line
- ●A pool looks shallower than it really is
- ●Rainbows form when light refracts through raindrops, splitting into colours
Why Does It Happen?
Light travels at different speeds through different materials. When it moves from air (fast) into water or glass (slower), it changes direction -- just like a car wheel turning when it goes from smooth road onto sand.
Key Vocabulary
Light Source
Something that produces its own light (e.g. the Sun, a lamp, a candle flame).
Reflection
When light bounces off a surface, like a mirror.
Refraction
The bending of light as it passes from one material to another.
Transparent
A material that lets all light pass through, allowing you to see clearly through it.
Translucent
A material that lets some light through but scatters it, making images blurry.
Opaque
A material that blocks all light and creates a shadow on the other side.
Worked Examples
You shine a torch at a mirror. Where will the light go?
Step 1: Light travels in a straight line from the torch to the mirror.
Step 2: The mirror is smooth and shiny, so it reflects the light.
Answer: The light will bounce off (reflect) at the same angle it hit the mirror. If it arrives at 45 degrees, it will reflect at 45 degrees.
Is frosted glass transparent, translucent, or opaque?
Step 1: Can you see clearly through frosted glass? No, but you can see blurry shapes and light.
Step 2: Does all light pass through? Some does, but it is scattered.
Answer: Frosted glass is translucent. It lets some light through but scatters it so you cannot see clear images.
Why does a pencil look bent when placed in a glass of water?
Step 1: Light travels at different speeds through air and water.
Step 2: When the light from the underwater part of the pencil exits the water, it bends (refracts).
Answer: Refraction bends the light at the air-water boundary, making the pencil appear bent or shifted where it enters the water.
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
Light travels in:
Question 2
A wooden door blocks all light. It is:
Question 3
When light bounces off a mirror, this is called:
Question 4
A straw in water appears bent because of:
Question 5
In reflection, the angle of incidence is equal to the:
Key Concepts Summary
- ●Light travels in straight lines at extremely high speed.
- ●Materials are transparent (all light through), translucent (some light), or opaque (no light).
- ●Reflection is light bouncing off a surface. The angle in equals the angle out.
- ●Refraction is light bending when it passes from one material to another (e.g. air to water).
- ●We see objects because light reflects off them and enters our eyes.