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The surface tension and vapour pressure ...

The surface tension and vapour pressure of water at `20^(@)C` is `7.28xx10^(-2)Nm^(-1)` and `2.33xx10^(3)Pa`, respectively. What is the radius of the smallest spherical water droplet which can form without evaporating at `20^(@)C`?

Text Solution

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Given, surface tension of water
`" "(S)=7.28xx10^(-2) N//m`
Vapour pressure (p) `=2.33xx10^(3)` Pa
The drop will evaporate, if the water pressure is greater than the vapour pressure.
Let a water droplet or radius R can be formed without evaporating.
Vapour pressure=Excess pressure in drop.
`therefore p=(2S)/(R)`
or `R=(2S)/(p)=(2xx7.28xx10^(-2))/(2.33xx10^(3))`
`=6.25xx10^(-5)` m
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