Question

Why Tyndall Effect is observed in colloids?

Answer 1

$\boxed{\textbf{DETAILED \quad EXPLANATION}}$

A Pure or a True Solution will have particles totally dissolved in the substance having a Molecular Size less than 1 nanometer, whereas, the light to get scattered or dispersed it should be in the range of 1 nanometer to 1000 nanometer, making true or pure solutions unable to exhibit the phenomenon of Tyndall Effect. Whereas, in a colloidal solution they contain macroparticles capable enough to scatter the light in a solution.

$\boxed{TYNDALL \quad EFFECT}$

$\textbf{John Tyndall}$ (Fellow of the Royal Society, a late 19th century physicist, rose to prominence by devising number of Experiments for the advancement if Human race) was the one who observed by observations and investigations of radiated heating source in a medium of Air should be neutralised by eliminating particulate matter which included, dust particles, water vapor, small microorganisms, etc. He used intensified light and projected it on air to be observable for seeing the particulate matter which evenly gets scattered around it, as, the impure mixtures or colloidal solutions get the light to get scattered, now coined and termed as, Tyndall Scattering Effect.

This is a special experiment which is performed in a dim or dark room with little to no light. After that the beam of light will enter the dim room making the dust particles surrounding the areas in the coming path visible to our naked eye, clear and clean.

The light or strong beam of light will follow through the passed path and enter into the path of colloidal or dispersed solution making different angles and hence can be viewed at different positions.

This strong beam of light will show up as a blurry or hazy beam or form a cone by the passing lens. Because of this the solution particulate matter will absorb this light beam or energy managing the light to emit itself in all the directions throughout the solution.

Light being mixed up in all directions and it's scattering is what is known to illuminate the light path of the beam in the colloidal projections and it's dispersed particle dispersion.

The methodology and the phenomenon of scattering of light in different directions or paths through a single strong bean by the medium or media of solution particles is regarded as Tyndall effects. Only colloidal solutions or the particles containing difference of dispersion can show this effect, any true solution with no mixture cannot exhibit the Tyndall effect.

This phenomenon has also been named as $\boxed{Willis-Tyndall \: \: Scattering}$ Effect which produces those dispersed light or small-looking dust particles oftenly seen in projection rooms in cinema halls, wavelength is approximated about 40 nanometers to 700 nanometers, if it comes in that range it will be a Tyndall Effect, whereas if it falls below the required minimum wavelength, it will be termed as $\boxed{Rayleigh's \: \: Scattering \: \: Effect}$.

Examples to illustrate by the methodology given as a experiment to observe Tyndall Effect will include some of these.

One Example would be to create a diluted colloidal Milk solution by adding at least half cup of water for spacing between the molecules in the colloid, this makes the scattering of the light inside the solution ultimately illuminating the whole colloidal solution with dust-like dispersed particles being visible to the naked eye. A skimmed or unpure milk can be used since it will contain some additional not required solutions and solutes.

Second example will be to produce a substance presented with high amounts of gelatinous mixtures, here, a projecting laser is pointed onto the substance with gelatin. Further on, gelatinous substance will exhibit the phenomenon of Tyndall Effect when it's equal projection is done throughout a glass containing the gelatinous colloidal dispersed solution, same goes for salt being dissolved into water to provide a hazy or colloidal solution for another excellent demonstration.

$\boxed{ADDITIONAL \quad INFORMATION \quad FOR \quad UNDERSTANDING}$

Coming back to the query stated (or just to add extra information for doubt clearance). Canopies of dense forests contain many water molecular droplets performing as a perfect colloidal solution present as a moisturised combination in vast quantities carried by the air. If a Sunlight prepares to infiltrate Canopies, entering throughout tiny water droplets, and, when multiple rays of sunlight fall on those droplets by a assisted media called "air", they evenly get scattered (as pitched and shown above). This produces the scattering effect with the assistance of Sunlight (Sun being the source) and Air (Being the medium to transfer it to you colloidal particulate solution or rain or water droplets) which is recognisable to ones naked eye, is called or termed as Tyndall effect.