Light and shadows · Year 3
Light travels from a source in straight lines. When it hits an opaque object it is blocked, leaving a shadow the same shape as the object. We see things because light from a source bounces off them into our eyes – our eyes do not send anything out. Shadows change size with the position of the light, and length with the time of day.
Key facts
- Light sources (the Sun, flames, bulbs, screens) make their own light; the Moon and most objects only reflect it.
- Transparent: lets light through clearly. Translucent: lets some through, blurred. Opaque: blocks it, making a shadow.
- Moving an object closer to the light makes its shadow bigger.
- Outdoor shadows are shortest at midday, when the Sun is highest, and point away from the Sun.
- Never look directly at the Sun – it can permanently damage your eyes.
Worked examples
Example 1
A 6 cm puppet is 20 cm from a small torch. The screen is 80 cm from the torch. How tall is the shadow?
Answer: 24 cm