- Define and explain Light Travels Straight in your own words
- Use key terms such as opaque accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on Light Travels Straight: learning that light travels in straight lines and cannot bend around corners.
Learning that light travels in straight lines and cannot bend around corners.
Key ideas
Light travels in straight lines
Light cannot bend around corners — it always moves in straight lines called rays. That is why you cannot see around a wall but you can see down a straight corridor. Shadows have sharp edges because light cannot curve around the object making them.
Shadows form when light is blocked
Stand in sunshine and your body blocks the Sun's rays, leaving a dark patch — your shadow — on the ground behind you. Only opaque objects make proper shadows; transparent glass lets the light straight through. The shadow always falls on the opposite side from the light source.
Key term — opaque: A material that light cannot pass through, so it makes a clear dark shadow.
Why can't you see someone standing around a corner?
Light travels in straight lines and cannot bend around the corner to reach your eyes.
Answer: Light travels in straight lines and cannot bend around the corner to reach your eyes.
- Believing light bends around objects Light travels in straight lines, which is exactly why shadows exist.
- Saying the Moon is a light source The Moon does not make its own light — it reflects sunlight towards us.
Practice
Glass is transparent, so light passes straight through instead of being blocked.
At midday the Sun is high overhead so light comes almost straight down; in the evening the Sun is low, so your body blocks rays at a shallow angle and the shadow stretches out.
The Sun and stars (also acceptable: lightning, fireflies, glow-worms).
No — a mirror reflects light from a real source; it does not produce light itself.
Quick check
Which of these best defines "opaque"?
You move a toy further from a lamp. What happens to its shadow on the wall?
- Light Travels Straight: learning that light travels in straight lines and cannot bend around corners.
- Light travels in straight lines: Light cannot bend around corners — it always moves in straight lines called rays.
- light source: Anything that gives out light, such as the Sun, a candle flame or a torch bulb.
- Watch out for: believing light bends around objects