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
I’d use a bubble machine as an analogue.
Have her and her friends pop as many bubbles as they can, then tell them the game’s to only pop the large ones, then give them an iPad and have the machine running.
Light is like bubbles that are travelling towards materials, some are excited to see all the bubbles and so will pop them all, those are dark.
Some are indifferent to the bubbles so all the bubbles go through, those are clear.
Some will only pop certain bubbles, letting the rest through, those are coloured.
I’d use a bubble machine as an analogue.
Have her and her friends pop as many bubbles as they can, then tell them the game’s to only pop the large ones, then give them an iPad and have the machine running.
Light is like bubbles that are travelling towards materials, some are excited to see all the bubbles and so will pop them all, those are dark.
Some are indifferent to the bubbles so all the bubbles go through, those are clear.
Some will only pop certain bubbles, letting the rest through, those are coloured.
Water is see-through because it lets light pass through it easily without changing the light’s direction too much. Light is made up of tiny particles called photons. When these photons travel through air, they can easily pass through because air is very thin. Water is thicker than air, but it is still not thick enough to stop most of the photons.
When light goes through something, like water, we call it transparent. Water is transparent because its molecules are arranged in a way that doesn’t block or scatter light much. This means we can see through water because the light can easily pass through it and reach our eyes, so we can see what’s on the other side.
Water is see-through because it lets light pass through it easily without changing the light’s direction too much. Light is made up of tiny particles called photons. When these photons travel through air, they can easily pass through because air is very thin. Water is thicker than air, but it is still not thick enough to stop most of the photons.
When light goes through something, like water, we call it transparent. Water is transparent because its molecules are arranged in a way that doesn’t block or scatter light much. This means we can see through water because the light can easily pass through it and reach our eyes, so we can see what’s on the other side.
It’s a bit hard to cover all the interactions in a way that a 4 year old would understand, but hopefully this will kind of make sense to the average person:
When light hits a material, two things happen. Some amount of light gets reflected, eg bounces off the material, and the remaining light is refracted, meaning it enters the material.
(The amount of light that is reflected vs refracted is determined by snells law, which requires the index of refraction of the two materials, eg air and water, or vacuum and air. Index of refraction can be wavelength dependent for some materials such as metal, meaning some metals reflect some colors more strongly than others)
As light travels through this material, some amount of it get absorbed. Some materials absorb a lot of light quickly (Eg solid surfaces such as rock, wood), some absorb slower such as leaves, grass, skin, murky liquids, and some absorb light very slowly such as pure water, air molecules, etc. (Metals absorb light immediately, they don’t have any diffuse/translucency) The further light travels through the medium, the more light gets absorbed.
The physical quantity that determines how much light is absorbed is called the extinction coefficient. This has been measured for a large number of materials. It can also be wavelength dependent, meaning some colors are absorbed more quickly. Pure water is a good example, it quickly absorbs red wavelengths, giving it an aqua color over a distance.
There is one other important component which is scattering. Pure water does not have any scattering, however it often has dissolved chemicals and small organic matter such as algae and plankton. As light transitions between the water medium and organic matter, it changes directions and non-green wavelengths are quickly absorbed by organic matter. This causes scattering which makes the medium appear murky or foggy. This is the same mechanism that causes fog to be hard to see through. Fog does not absorb much light, however when light hits it, it tends to scatter in all directions, this is determined by something called a phase function. Some mediums scatter light in many directions causing haze, such as fog or air, whereas others scatter most of the light forward, such as pure water. (Two types of common scattering are rayleigh scattering and mie scattering, these contribute to the color of the sky, and the hazy halo you see around the sun)
(Source: I have spent years working on computer graphics algorithms and have a good fundamental understanding of some of the equations and physics of light)
It’s a bit hard to cover all the interactions in a way that a 4 year old would understand, but hopefully this will kind of make sense to the average person:
When light hits a material, two things happen. Some amount of light gets reflected, eg bounces off the material, and the remaining light is refracted, meaning it enters the material.
(The amount of light that is reflected vs refracted is determined by snells law, which requires the index of refraction of the two materials, eg air and water, or vacuum and air. Index of refraction can be wavelength dependent for some materials such as metal, meaning some metals reflect some colors more strongly than others)
As light travels through this material, some amount of it get absorbed. Some materials absorb a lot of light quickly (Eg solid surfaces such as rock, wood), some absorb slower such as leaves, grass, skin, murky liquids, and some absorb light very slowly such as pure water, air molecules, etc. (Metals absorb light immediately, they don’t have any diffuse/translucency) The further light travels through the medium, the more light gets absorbed.
The physical quantity that determines how much light is absorbed is called the extinction coefficient. This has been measured for a large number of materials. It can also be wavelength dependent, meaning some colors are absorbed more quickly. Pure water is a good example, it quickly absorbs red wavelengths, giving it an aqua color over a distance.
There is one other important component which is scattering. Pure water does not have any scattering, however it often has dissolved chemicals and small organic matter such as algae and plankton. As light transitions between the water medium and organic matter, it changes directions and non-green wavelengths are quickly absorbed by organic matter. This causes scattering which makes the medium appear murky or foggy. This is the same mechanism that causes fog to be hard to see through. Fog does not absorb much light, however when light hits it, it tends to scatter in all directions, this is determined by something called a phase function. Some mediums scatter light in many directions causing haze, such as fog or air, whereas others scatter most of the light forward, such as pure water. (Two types of common scattering are rayleigh scattering and mie scattering, these contribute to the color of the sky, and the hazy halo you see around the sun)
(Source: I have spent years working on computer graphics algorithms and have a good fundamental understanding of some of the equations and physics of light)
If you tie a rope to a pole and move your arm up and down while holding the other end, you’ll see a wave form in the rope. The faster you move your arm, the closer the hills and valleys in the wave will be.
Light does the same thing, but at a much smaller size. More specifically, different colors of light “wave” at different speeds.
The faster it waves, which we see as color, the more energy the light has. Red light waves the slowest, blue light waves the fastest. Any slower or faster, and we can’t see it.
The reason some things, like water, are transparent is because materials only reflect certain energy levels (colors) of light. We can only see light that enters our eyes, and since most visible light passes through water, we see through it with few problems.
If you tie a rope to a pole and move your arm up and down while holding the other end, you’ll see a wave form in the rope. The faster you move your arm, the closer the hills and valleys in the wave will be.
Light does the same thing, but at a much smaller size. More specifically, different colors of light “wave” at different speeds.
The faster it waves, which we see as color, the more energy the light has. Red light waves the slowest, blue light waves the fastest. Any slower or faster, and we can’t see it.
The reason some things, like water, are transparent is because materials only reflect certain energy levels (colors) of light. We can only see light that enters our eyes, and since most visible light passes through water, we see through it with few problems.
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