======Brownian Motion in a Smoke Cell======


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**Alternative titles:** Smoke Particle Motion Under Microscope
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====Summary====                   
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====Procedure====  
  - Generate smoke using a paper straw or similar safe source.  
  - Fill a smoke cell with the smoke and cover it with a glass cover-slip to reduce loss of particles.  
  - Place the smoke cell on the microscope stage and connect the light source to a low-voltage power supply.  
  - Focus the microscope carefully until tiny bright specks (smoke particles) come into view.  
  - Observe the movement of the specks over time, noting their random jiggling and occasional disappearance as they move in and out of focus.



====Links==== 
A Smoke Cell demonstrating Brownian Motion in Air. - FranklyChemistry: 
{{youtube>ygiCHALySmM?}}\\

Observing Brownian Motion with a Smoke Cell - Physics with Simon Poliakoff: 
{{youtube>2Lthk5K3z7A?}}\\

📄 Brownian motion in a smoke cell - Institute of Physics: [[https://spark.iop.org/brownian-motion-smoke-cell]]\\


====Variations====
  * Use a camera or projector so the entire class can observe at once.  
  * Replace smoke with polystyrene microspheres suspended in water.  
  * Demonstrate the idea using a loudspeaker vibrating table tennis balls and a balloon as a large-scale analogy.



====Safety Precautions====
  * Do not allow sunlight to reflect up through the microscope.  
  * Use only small, controlled sources of smoke such as paper straws; avoid hazardous or plastic materials that may release harmful fumes.  
  * Clean the smoke cell regularly to maintain visibility and reduce residue build-up.  
  * Handle glassware with care to avoid breakage.




====Questions to Consider====
  * Why do the smoke particles appear to jiggle randomly? (They are being bombarded by invisible air molecules moving at high speeds.)  
  * Why might some particles drift slowly in one direction? (Large-scale convection currents or uneven air movement, which are not part of the true Brownian motion.)  
  * How does this experiment support the kinetic theory of gases? (It provides evidence that air molecules are real and in constant motion, even though they cannot be seen directly.)  
  * How small must air molecules be compared to smoke particles? (Much smaller—orders of magnitude smaller—since they can move visible smoke particles through collisions.)