P4 Science - Light & Shadows

Sources of Light

Sources of light are objects that give off their own light.

They can be natural (like the Sun and fire) or man-made (like lamps).

Type	Examples
Natural sources	Sun, fire, stars, firefly, lightning
Man-made sources	Lamps, torches, lighted candle

What about objects that do not give off light?
They can only be seen when light from a light source reflects off the object and enters our eyes.
Examples: Moon, mirrors

Properties of Light

Light travels in straight lines
Light can be reflected
Light can be blocked

Transmission of Light

Materials are classified by how they interact with light:

Type	Description	Example	Can you see through it?
Transparent	Allows most light to pass through	Window pane, clear glass, clear plastic	Yes, clearly (clear vision)
Translucent	Allows some light to pass through	Frosted glass door, frosted glass	Only partially (blurry vision)
Opaque	Allows no light to pass through	Mirror, wood, metal	Not at all (no vision)

Quick Review — Memory Trick:
Transparent = clear vision | Translucent = blurry vision | Opaque = no vision

Shadows

Shadows are formed when light from a light source, travelling in straight lines, is blocked by a translucent or opaque object.

Shadows prove that light travels in straight lines.
Shadows prove that light can be blocked.

Conditions to Form a Shadow:

A light source
An object (opaque or translucent)
A screen/surface for the shadow to fall on (usually opaque)

Types of Shadows:

Object Type	Shadow Formed
Opaque	Dark shadow
Translucent	Light shadow
Transparent	No shadow

Size of Shadows:

Object moves closer to light source → Bigger shadow
Screen moves further from object → Bigger shadow

Shadows During the Day:

As the Sun moves across the sky, it changes the angle of light, affecting shadows.

Time of Day	Sun's Position	Shadow
Morning	Rises in the East	Long shadow pointing West
Noon	Overhead (directly above)	Shortest shadow (under object)
Evening	Sets in the West	Long shadow pointing East

Key Takeaways

Sources of light give off their own light — natural (Sun, fire) and man-made (lamps, torches).
Moon and mirrors only reflect light — they are not sources of light.
Properties of light: travels in straight lines, can be reflected, can be blocked.
Transparent = most light passes (clear vision) | Translucent = some light passes (blurry vision) | Opaque = no light passes (no vision).
Shadows form when light is blocked by a translucent or opaque object.
Three conditions: light source + object + screen/surface.
Opaque → dark shadow | Translucent → light shadow | Transparent → no shadow.
Closer to light source or further screen → bigger shadow.
Morning: Sun in East, long shadow pointing West. Noon: Sun overhead, shortest shadow. Evening: Sun in West, long shadow pointing East.