Light and Optics
Grade 4 · Science · Study Guide
Discover how light travels, bends, and bounces to help us see the world.
Light is a form of energy that travels in straight lines called rays. It is the fastest thing in the universe, traveling about 186,000 miles per second. Light travels as waves, and different colors of light have different wavelengths. When all the colors combine, we see white light.
When light hits an object, three things can happen. Light can be reflected (bounced back), like when you see yourself in a mirror. Light can be absorbed (taken in), which is why dark objects get hot in the sun. Light can be transmitted (passed through), like through a glass window. When light passes from one material into another (like from air into water), it bends — this is called refraction. Refraction is why a straw in a glass of water looks bent.
Lenses and mirrors are tools that use reflection and refraction. A concave lens spreads light apart and makes things look smaller. A convex lens focuses light together and can magnify objects. Prisms use refraction to separate white light into its rainbow of colors: red, orange, yellow, green, blue, indigo, and violet.
Key terms
- Light
- A form of energy that travels in waves at extremely high speed
- Reflection
- When light bounces off a surface
- Absorption
- When light is taken in by a material rather than reflected or transmitted
- Refraction
- The bending of light as it passes from one material to another
- Transparent
- A material that allows light to pass through it clearly
- Opaque
- A material that does not allow light to pass through it
Flashcards
- Reflection
- Light bouncing off a surface
- Refraction
- Light bending as it passes from one material to another
- Absorption
- When a material takes in light rather than reflecting it
- Transparent
- Allows light to pass through clearly (glass, water)
- Opaque
- Blocks light from passing through (wood, metal)
- Prism
- A glass shape that separates white light into rainbow colors
Practice questions
What is it called when light bounces off a surface?
- Refraction
- Absorption
- Reflection
- Transmission
Show answer
Answer: Reflection
Reflection is when light bounces off a surface. Mirrors are designed to reflect nearly all light that hits them.
What happens to light when it passes from air into water?
- It speeds up
- It bends
- It disappears
- It turns white
Show answer
Answer: It bends
When light passes from air into water, it slows down and bends — this is called refraction. It's why a straw in water looks bent.
Light travels in straight lines.
Show answer
Answer: True
Light always travels in straight lines called rays unless it is reflected or refracted by a material.
An opaque object allows light to pass through it.
Show answer
Answer: False
An opaque object blocks light from passing through. Transparent objects (like glass) allow light to pass through.
The bending of light as it passes from one material to another is called ___.
Show answer
Answer: refraction
Refraction happens when light changes speed as it enters a new material, causing it to bend at the surface.
Fun facts
- Light from the sun takes about 8 minutes to reach Earth — traveling 93 million miles!
- A rainbow forms when sunlight is refracted and reflected inside millions of water droplets.
- Cats have a special layer behind their eyes that reflects light, helping them see in near-darkness.
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