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Physics Question. Need help please.

Guys. Can you help me out with this?
Really need to figure this out and I can't do it.

When a 0.6 mm diameter oil droplet is placed on a large surface of still water it spreads out to give a circular film of diameter 0.5 m. With an explanation of your method, roughly estimate the size of a
single molecule of the oil. You should state and justify any assumptions you make.

Thank you if you can solve this. I can't find anything online :frown:
Wel;come to TSR Physics.

You didn't look very far!

Just search on "size of an oil drop experiment" or similar.
All explained here...
http://www.nuffieldfoundation.org/practical-physics/estimating-size-molecule-using-oil-film
http://www.schoolphysics.co.uk/age16-19/Thermal%20physics/Kinetic%20theory%20of%20matter/text/Molecular_size_oil_drop/index.html
(edited 10 years ago)
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natninja
21
Original post by fhamid
Guys. Can you help me out with this?
Really need to figure this out and I can't do it.

When a 0.6 mm diameter oil droplet is placed on a large surface of still water it spreads out to give a circular film of diameter 0.5 m. With an explanation of your method, roughly estimate the size of a
single molecule of the oil. You should state and justify any assumptions you make.

Thank you if you can solve this. I can't find anything online :frown:


Sorry for the brevity of my answer - I got set a nice big Quantum mech sheet 10 mins ago due in at 6am tomorrow... (The joys of certain universities....)

But essentially your spherical droplet is changing shape into a cylinder that has the height of a single molecule (That is the assumption you make btw - it's not a bad approximation to be fair) In terms of justification for that - it spreads out to cover a maximum area and the height cannot be less than the diameter of a molecule (assuming spherical molecules.../random orientation of molecules)

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