Light and shadow [replacing FYH109]

Leon is getting camping gear from the basement. Suddenly, the light goes out! It’s so dark, Leon can’t see anything. Luckily, he’s got an electric torch. He can use the light from it to help him see things.

Light is a form of energy, emitted by things such as fire, electric light bulbs, or stars, including our Sun. Something that emits light is a light source. Light from a light source travels through space in all directions, but always only in straight lines. Most things around you, however, do not emit light. How come you can still see them?

It’s because light is reflected by objects. Your eyes sense the light, both emitted and reflected, and your brain interprets it as visual images. If there is little or no light, you can’t see much. When Leon switches on the torch, the light bulb inside it becomes a light source. Hey, look!

There’s a spider, hanging on its web between Leon’s torch and the wall! When the light from the torch reaches the spider, it can’t reach any further. All the light around the spider continues and hits the wall. Where the blocked off light is “missing,” a dark spot forms on the wall, in the shape of the spider - a shadow. So, a shadow is created behind an object that doesn’t let light pass through it.

But why is the shadow of the spider so much bigger than the spider itself? The size of a shadow depends on the distances between the light source, object, and surface where the shadow lies. If the spider hangs far away from the light source, it blocks very little light, so the shadow appears small. But if the spider is close to the light source, it covers a much bigger portion of the light emitted, so the shadow is bigger. The shape of the shadow also changes depending on the position of the object and the light source.

If the light source is positioned so that light falls straight onto the object, the shadow will be short, reflecting the shape of the object quite accurately. But if light falls on the object at a lower angle, the shadow becomes longer and skinnier. Shadows form if an object is placed between a light source and a surface on which the light falls. The size and shape of a shadow can change depending on how these three things are positioned in relation to each other. But do all objects cast shadows?

Let’s investigate! A magnifying glass is exactly what we need to test this. Hold the magnifying glass between the source of light and a wall, Leon. Does it cast a shadow? Only the frame the glass is placed in!

The frame is made of a solid, opaque material that doesn’t let the light through, so it creates a shadow. But the glass lens mounted inside the frame is transparent. You can see through it, which means the light can pass through. If light can pass through an object, it doesn’t create a shadow. Can you think of any other objects that won’t have a shadow?

Maybe you can pick a few things around you and try to predict what their shadows will look like. Try changing the colour of the light, or add another light source! Keep experimenting, and see what else you can discover about light and shadow!