Getting rid of shadows
Look down at your keyboard. Are the keys making any shadows? You should be able to see some key shadows on the top line of keys where you find 1 and ! and + and =. Which way do the shadows point? Their direction gives you a clue about where the light is that is causing the shadow. To find the light source, simple look in the opposite direction to where the light is pointing and there it is! What is the light source that is causing shadows on your keyboard?

Now go on a shadow hunt. Look for shadows in every room. Look also for the source of light that is causing the shadow. You may find it to be a light in a ceiling, a wall light, a table lamp or light through a window or door. Everywhere you go you should be able to find shadows.

If you go outside to look for shadows on a sunny day, you will find very dark shadows with sharp edges. This is how everyone thinks of shadows. When you look inside a building you may find the shadows much more difficult to see. When you do find them they may be pale with fuzzy edges. As shadows are not always very dark you may wonder if it would be possible to get rid of them. Before you try, you should think about what you know about the science of shadows to question whether it might be possible.

When a light source shines it sends out huge numbers of rays of light. They travel in straight lines. If a ray of light travels from a source and hits a surface like the ground or a wall it lights or illuminates that surface. Many objects are opaque. That means they do not let light rays go through them. A light ray is stopped when it strikes an opaque object. Its path is blocked and it cannot continue on its way to light the ground or wall. As there is no light on the other side of the object, the area is dark because darkness is an absence of light. This dark place is called a shadow.

So far you have thought about one light source and one shadow. What would happen if there were two light sources shining from different directions? According to what you know, the light rays from the second light source should also be blocked by the object and make a shadow. It should be possible to have two shadows. Try this experiment to find out. Look at the shadows on your keyboard and switch on a torch. Point the torch so its light shines in a different direction from the light source that made the shadows. When you do this you see the keys have a second shadow. In some places it may overlap the first shadow.

Now, think about a shadow being a place where light is absent. What would happen if you shone your torch in the opposite direction to the light source that makes shadows of the keys? If light from the torch entered the place where light was absent it would no longer be dark. This means that if this were true the shadow would disappear. Take your torch, switch it on and point it down on the keyboard in the direction of the light source that is making the shadows. Sweep the beam of light along the keys and you should see the shadows disappear. Your thinking was correct. When light enters a shadow, the darkness is removed and the shadow disappears.

On your shadow hunt you found pale shadows. What has happened to them? If the shadows are pale and fuzzy it seems that some light is entering the place where the shadow is cast. Where could this light be coming from? This is where a bit more scientific knowledge comes in. When a light ray strikes a surface it may be reflected from it. The reflected light ray then travels on its way until it strikes another surface. If it strikes a surface in a shadow it will brighten or illuminate that surface. This will remove some of the darkness and make the shadow appear paler. The best surface for reflecting light is a mirror. You can test this idea about reflecting light making shadows paler in the following way. Take a small mirror and point at the light which makes the shadows of the keys. Now direct the mirror down onto the keyboard. You should find that the shadows become paler owing to the reflected light.

Next time you look for shadows look for the light sources too, You may find that they give an object two or more shadows or that one light source makes a shadow paler. Look also for reflecting surfaces like mirrors or white surfaces: the light from them can alter shadows too.

What causes light?
A light source is a place where light is produced. The light may be made when something burns. Fires and candles provide light in this way. Light may be made when electricity passes through them. Electric lamps and fluorescent tubes make light in this way. The Sun and stars make light by changing a gas called hydrogen into a gas called helium.

Does light from these different sources behave in the same way?
Yes, it does. The light rays produced from these sources travel in straight lines.

What can happen to a light ray when it hits a surface?
If the surface is made from an opaque material the path of the light ray is blocked. Some light rays are simply absorbed by the material but others are reflected. If the surface is made from a translucent material, some light rays may pass through but as they do so they are reflected off substances in the material and follow a different path when they come out on the other side. Some light rays may be absorbed by the material while yet others may be reflected back the way they came. If the surface is made from a transparent material most of the light rays will pass through and may not even change their paths. A few light rays will be absorbed and some will be reflected back the way they came.

Do all surfaces absorb the same amount of light?
No. A white surface absorbs the least light and reflects the most. A dark surface absorbs the most light and reflects the least. When you are mixing paint to make a darker colour you mix in a substance that absorbs more light. This makes the paint look darker.

Can light and dark surfaces in a room affect shadows?
Yes.
Light surfaces will reflect the most light. This may shine into shadows and make them paler. Dark surfaces reflect much less light and so the shadows remain dark.

Where can shadows be removed by a light-reflecting surface?
They
can be removed at a photographer's studio. When you have a photograph taken, a lamp is placed on one side of your face to light it and make a clearer picture. However, features on your face, such as your nose, cast a shadow. These shadows are removed by placing a light-reflecting material on the other side of you. This surface reflects the light from the lamp onto your face. The light shines into the shadows and they disappear.

Where are lights used to remove shadows?
Lights in ceilings of classrooms are arranged to reduce shadows and make them paler. This is done because dark shadows make it difficult to read or try practical work like science. In an operating theatre the lights are arranged to remove all shadows so the surgeons can see clearly to work on their patient.

You were asked, in the story, to think about science before doing an experiment. Is this sensible?
It is very sensible. You should think about what you have learned before you try some experiments. This will help you make a better experiment and may help you make even more discoveries. Scientists always think about what they know and what they are trying to find out before they make an experiment.