Let\'s look at the surface tension of the liquid metal mercury. Mercury has an u

Question

Let's look at the surface tension of the liquid metal mercury. Mercury has an unusually high surface tension, about 465 dyn/cm. Calculate the excess pressure inside a drop of mercury 4.00 mm in diameter.

SET UP AND SOLVE We first convert the surface tension to SI units:

=465dyn/cm=465×103N/m

Now we have

ppatm===2R=(2)(465×103N/m)0.00200m465Pa0.00459atm

REFLECT The excess pressure (the difference between the inside and outside pressures) is a very small fraction of the atmospheric pressure.

What would the diameter of the drop be if the inside pressure were 2.115 atm ?

Explanation / Answer

excess pressure = 2*T*R = 2.115*1.01*10^5 - 1.011*10^5 = 2*0.465*R
R = 121091.3978 m

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