Eli5 Why is water see through?

Question

My 4 year old asked me and I think it’s a rather good question that I would like to answer so she understands. Thanks 🙏🏻

In: 1926

Answer 1

Well, have you ever played with a ball in a swimming pool? When the ball is underwater, it looks bigger and distorted, right? That’s because the water bends or refracts the light that passes through it.

Now, imagine if you had a really tiny ball that was made up of water molecules. When light passes through these tiny water molecules, it also gets bent or refracted, just like in the swimming pool.

But here’s the thing: when the light gets refracted, it doesn’t get absorbed by the water molecules. Instead, it just gets redirected in a different direction. This means that the light can keep traveling through the water without being absorbed or scattered, which allows it to pass through the water and reach our eyes, making the water appear transparent.

So in simple terms, water is transparent because it doesn’t absorb or scatter light, but instead bends or refracts it, allowing the light to pass through it without being absorbed, and reach our eyes.

Some materials, on the other hand, are not transparent because they absorb or scatter light instead of bending or refracting it like water.
For example, if you shine a flashlight through a piece of wood or a leather sheet, the light won’t pass through it easily like it does with water. Instead, the light will be absorbed or scattered by the wood or the sheet, which makes these materials appear opaque or non-transparent.
Opaque materials have a lot of atoms or molecules packed together very tightly, which makes it difficult for light to pass through them. When light hits an opaque material, the atoms and molecules in the material absorb the light’s energy and re-emit it in many different directions, which causes the light to scatter and reflect back towards us, making the material appear solid and not see-through.
In summary, the difference between transparent and opaque materials lies in how they interact with light. Transparent materials bend or refract light, allowing it to pass through without being absorbed or scattered, while opaque materials absorb or scatter light, preventing it from passing through easily and making the material appear solid and non-transparent.