Topics · Primary Science · Energy: Light & Shadows
Light and shadows
Light travels in straight lines. A shadow is where an object blocks it. Almost every question on this topic follows from those two sentences — including all the ones about shadow size.
- 294 exam papers analysed
- appears in 78% of P4 Science papers
- ~3 min read
01 Light travels in straight lines
Light goes straight until something stops it or turns it. It does not bend round corners, which is why you cannot see round a wall.
A shadow forms because an object blocks the light, leaving a dark patch behind it in the shape of the object.
Three things are needed for a shadow: a light source, an object that blocks light, and a surface for the shadow to fall on. A question removing any one of them has no shadow as its answer.
02 What blocks light, and what does not
How much light gets through decides whether there is a shadow and how dark it is.
| Material | Light passes through? | Can you see clearly through it? | Shadow |
|---|---|---|---|
| Opaque (wood, metal) | ✗ | ✗ | dark, sharp |
| Translucent (frosted glass) | some | ✗ | faint |
| Transparent (clear glass) | ✓ | ✓ | almost none |
03 What changes a shadow's size
This is the most-tested part, and it has one rule with two halves.
- Move the object closer to the light → the shadow gets bigger. It blocks more of the spreading light.
- Move the object closer to the screen → the shadow gets smaller, down to the object's own size.
- Move the light closer to the object → bigger shadow; further away → smaller.
- The object's own size never changes, and neither does the light. Only the distances do — say which distance changed, not just “it got bigger”.
04 Shape, direction and the sun
A shadow has the outline of the object as seen from the light, so turning an object changes its shadow's shape. A disc gives a circle face-on and a line edge-on.
A shadow always falls on the opposite side from the light. Move the light to the left and the shadow goes right.
Outdoors: the sun is low in the morning and evening, giving long shadows, and high at midday, giving short ones. The shadow points away from the sun and swings round through the day — which is how a sundial works.
05 How to say them
These are words most children have never said out loud, and a word you cannot say is a word you avoid using. Capitals mark the syllable you lean on. Tap the speaker to hear it.
- light sourcemore than onelight sources
Something that gives out its own light — the sun, a lamp, a candle. The moon is not one; it reflects the sun's light.
- opaquesayoh-PAYK
Lets no light through, so it casts a dark shadow.
- translucentsaytranz-LOO-suhnt
Lets some light through but you cannot see clearly, so the shadow is faint.
- transparentsaytrans-PA-ruhnt
Lets light through and you can see clearly, so there is almost no shadow.
- shadowmore than oneshadows
The dark area behind an object where light has been blocked.
- reflectsayri-FLEKT
To bounce light off a surface. A mirror reflects light well.
06 What each level is tested on
The same topic, asked differently as it goes up. The percentage is the share of papers at that level in which it appears.
- P4
Light sources, how shadows form, and which materials block light.
Practise P4 Energy: Light & Shadows — 10 questions →78% of P4 papers
- P5
What changes a shadow's size and shape, and fair tests about it.
Practise P5 Energy: Light & Shadows — 9 questions →43% of P5 papers
- P6
Light in longer questions, reflection, and shadows outdoors through the day.
Practise P6 Energy: Light & Shadows — 9 questions →71% of P6 papers
07 Mistakes worth knowing about
Each of these is wrong. Decide why before you open it.
“The shadow got bigger because the object got bigger.”
The object never changed. Say which distance changed — object to light, or object to screen.
“Light bends round the object, which is why the shadow has soft edges.”
Light travels in straight lines. Soft edges come from the light source being wide rather than a point.
“The moon is a light source.”
It reflects light from the sun. A light source gives out its own light.
“A transparent object casts a dark shadow.”
Light passes through it, so there is almost no shadow. Only opaque objects give a full dark one.
“Shadows are longest at midday.”
Shortest. The sun is highest at midday; shadows are longest when it is low, in the morning and evening.
Now try it
28 questions across 3 levels, marked as you go with the working shown.