Exploring Light & Particles in Water

• An Architect
In summary, the brightness of illuminated particles in water changes depending on the angle at which it is viewed due to the straight line nature of light and the fact that light can only be seen when it is either directly reaching the observer or being reflected off another object. However, when the experiment involves smoke particles instead of water and particles, the scattering of light is dependent on the size of the particles, with smoke particles being slightly bigger and causing less color effects. Additionally, it is noted that there should not be much scattering from salt in water due to the dissolving nature of salt.
An Architect
light and particles in water

I'm an architecture student with a very basic knowledge of phyics! My project involves shining a beam of light through water that contains particles (in this case salt). What I want to know is why the brightness of the illuminated particles changes when you look at it from different angles i.e. the beam almost disappears when you stand perpendicular to it and the intensity increases as you walk through a 90 degree angle to stand parallel to the beams of light (caught in the headlights!). Obviously, when you stand facing the beam of light its at its brightest, but why is is it that you don't see the reflection of light off the salt when standing perpendicular to the beam direction?

Last edited:
uh ? Its optics!

When you stand in front of a headlight, the intensity is more because the light rays are coming from the headlight straight to your eyes. In the other case, they aren't.

2 simple rules
Light travels in straight lines
You can only see light which ends up in your eye!

So you can only see light which either goes directly form the source to you or is reflected from another object.
In the case of the fog tank - you can see the brightest light looking straight through the tank toward the light source.
As you go to the side you see light which has been only slightly deflected by hitting a few particles, then at 90deg you onlysee light which happens to have bounced off particles at exactly 90deg. Finally as you go round the back it brightens again because you see light which has bounced back from any particle in the fog.

It's all a question of probabilities and the number of available paths - it's a bit like the path of a ball in a pinball machine.

equivalent set up but with smoke

ok, I understand.

I've set up a similar experiment projecting a beam of light through smoke (rather than particles and water) but in this case you can see the beam of light reflected off the smoke particles from whichever angle you view it. How come there's a difference?

The scattering depends on the size of particles.
For paticles roughly the size of a wavelenght of light raleigh scattering (http://en.wikipedia.org/wiki/Rayleigh_scattering) is th emost important, this is about the size of dust in the air. Smoke particles are a little bigger so you don't get the colour effects - they scatter all wavelengths similairly.

Re-reading your original post, you sholuldn't get much scattering from salt in water - it dissolves so there shouldn't be any particles to scatter from?

What is the importance of exploring light and particles in water?

Exploring light and particles in water is important because it helps us understand how light behaves and interacts with matter in aquatic environments. This knowledge is crucial for various fields such as oceanography, climate science, and marine biology.

How does light travel through water?

Light travels differently through water compared to air. In water, light is quickly scattered and absorbed due to the presence of particles and dissolved substances. This results in reduced visibility and changes in the color and intensity of light as it travels deeper into the water.

What are some techniques used to explore light and particles in water?

Some common techniques used to explore light and particles in water include spectrophotometry, fluorometry, and laser diffraction. These methods allow scientists to measure the amount of light absorption, scattering, and fluorescence in water samples, providing valuable information about the properties of particles and dissolved substances in the water.

How do particles affect the behavior of light in water?

Particles in water can significantly impact the behavior of light. The size, shape, and composition of particles can affect the way light is scattered, absorbed, and transmitted. For example, larger particles tend to scatter light more, while smaller particles tend to absorb more light, leading to changes in the color and clarity of water.

What is the role of light and particles in the marine ecosystem?

Light and particles play a crucial role in the marine ecosystem. Light is essential for photosynthesis, which is the process by which plants and algae produce energy. Particles in the water can also serve as food sources for various organisms, and they can help regulate temperature and nutrient levels in the water. Understanding the behavior of light and particles in water is crucial for studying and protecting marine life.

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