Estimated time: 45 minutes | Difficulty: Medium | Ref: KS2-LI-4a
Learning objective: Investigate how shadow size relates to light source position
Use the pathway to build a clear mental model. Open each node and answer the check question.
When an object is close to the light source, it blocks a larger proportion of the spreading light rays, creating a larger shadow. When the object moves further from the light source (but stays the same distance from the screen), the shadow becomes smaller because the object blocks a smaller proportion of the light cone. Think of it like holding your hand close to a torch versus far away.
Check: If you move a puppet closer to a lamp, what happens to its shadow on the wall?
When an object is close to the screen/surface, the shadow is about the same size as the object. When the object moves further from the screen (keeping the light source position the same), the shadow gets larger because the blocked light rays have more distance to spread out. The light rays diverge (spread apart) as they travel, making the shadow expand.
Check: If you hold your hand halfway between a lamp and the wall, will your shadow be larger or smaller than your actual hand?
Light from most sources (like lamps and torches) spreads out in all directions. This spreading is key to understanding shadow size. Because light rays diverge (spread apart) as they travel away from the source, an object positioned in this spreading cone of light will block more or fewer rays depending on its position. Closer to the source = bigger shadow; closer to the screen = smaller shadow.
Check: Why does light from a nearby lamp create shadows that change size, while sunlight creates shadows that stay more constant?
The angle of the object relative to the light and screen affects shadow shape. Tilting an object changes which parts block light, altering the shadow's appearance. A circular disc held flat might cast a circular shadow, but tilted it casts an oval. The angle of the light source also matters - the Sun low on the horizon creates long shadows, while overhead it creates short ones.
Check: Why are your shadows longest in the morning and evening, but shortest at midday?
The size of a shadow depends on the positions of the light source, the object, and the screen (surface where the shadow appears). Understanding these relationships helps us predict and control shadow sizes.
Object CLOSE to the light source → LARGER shadow
When an object is positioned close to a light source, it intercepts a larger portion of the diverging (spreading) light rays. The blocked rays create a larger shadow region on the screen behind.
Object FAR from the light source → SMALLER shadow
When the object is moved away from the light source (but the screen stays in the same place), it now blocks a smaller proportion of the spread-out light, resulting in a smaller shadow.
Object CLOSE to the screen → SMALLER shadow (similar to object size)
When the object is very close to the surface where the shadow falls, the blocked light rays haven't had much distance to spread, so the shadow is roughly the same size as the object.
Object FAR from the screen → LARGER shadow
When the object is further from the screen, the blocked light region has more distance to expand, creating a larger shadow.
Most light sources (lamps, torches, candles) emit light that diverges - spreads out in all directions like a cone. This is different from the Sun, which is so far away that its rays are essentially parallel (not spreading). With diverging light, an object's position dramatically affects how much of the light cone it blocks.
Shadow shape is affected by:
Understanding shadow size and shape is essential for shadow puppetry, photography, filmmaking, and even architecture (designing buildings to control light and shade). It also explains everyday observations like why your shadow is longest in the morning and evening but shortest at noon.
Shadow puppet performances are regularly staged at UK venues like the Little Angel Theatre in London and the Puppet Theatre Barge. Shadow puppeteers are experts at controlling shadow size and shape. By moving a puppet closer to the light source, they can make a character appear to grow larger - perhaps a monster becoming more threatening! Moving the puppet closer to the screen makes it smaller and sharper. Tilting and rotating the puppet changes its shape, allowing a flat figure to create dynamic, 3D-looking movements. These techniques bring simple cut-out shapes to life on stage.
Your shadow changes dramatically during a day in Britain. In the early morning and late evening, when the Sun is low near the horizon, your shadow can be incredibly long - perhaps 10 or 20 times your height! The light hits you at a low angle, creating an elongated, stretched shadow. At midday (especially in summer when the Sun is higher), your shadow is much shorter - sometimes barely visible directly beneath your feet. This happens because the Sun's angle changes throughout the day. On the summer solstice (around 21st June), shadows are shortest; on the winter solstice (around 21st December), even midday shadows are quite long because the Sun never gets very high in British skies.
British film and television studios (like Pinewood and Elstree in Hertfordshire, or BBC studios in Salford) use sophisticated lighting to control shadow size and shape. Cinematographers and lighting directors carefully position lights to create specific shadow effects. A light placed low creates long, dramatic shadows (often used in horror films). Multiple lights from different angles can eliminate unwanted shadows or create interesting patterns. Moving a key light closer to an actor creates a larger, softer shadow. The British film industry has pioneered many lighting techniques that manipulate shadows for storytelling effect.
Around 240 BCE, the Greek scientist Eratosthenes used shadow size to calculate the Earth's circumference! He knew that at noon on the summer solstice in Syene (Egypt), the Sun cast no shadow (it was directly overhead). But in Alexandria, 800 km north, a vertical stick DID cast a shadow at the same time. By measuring the shadow's angle and knowing the distance between cities, he calculated the Earth's circumference to within about 2% of the actual value - using just shadows! British scientists and mathematicians later refined these techniques. Understanding how the Sun's angle affects shadow length was crucial to this amazing discovery.
Answer all questions, then check your answers. Your quiz result is saved on this device.
Wrong: "Moving the object closer to the light source makes the shadow smaller."
Right: Moving an object CLOSER to the light source makes the shadow LARGER (the object blocks more of the spreading light). Moving it FURTHER from the source makes it smaller. Think of it this way: hold your hand really close to a torch, and you block almost all the light. Move it away, and you only block a small part of the spreading beam.
Wrong: "It doesn't matter which distance you change - the effect is the same."
Right: These have OPPOSITE effects! Object closer to source → bigger shadow. Object closer to screen → smaller shadow. Both relationships exist because light diverges (spreads out) as it travels. A bigger light-to-object distance AND smaller object-to-screen distance BOTH make shadows smaller.
Wrong: "If I stand closer to the Sun, my shadow will be bigger."
Right: The Sun is 150 million kilometres away! Moving a few metres makes no difference. Sunlight rays reach Earth nearly parallel, so shadow size from sunlight depends mainly on the Sun's ANGLE in the sky (time of day), not your position relative to the Sun. Low Sun = long shadows; high Sun = short shadows. This is different from nearby light sources like torches or lamps.
Wrong: "The shadow gets bigger because the object somehow looks bigger to the light."
Right: The object stays exactly the same size! The shadow size changes because of how much of the diverging light the object BLOCKS. When close to the source, the object blocks a larger portion of the narrow light cone. Further away, the cone has spread out and the same-sized object blocks a smaller proportion. It's all about geometry and light spreading, not the object changing.