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Use of the Barometer equation

by Unto
Tags: barometer, equation
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Dec22-09, 06:10 PM
P: 121
Venus's atmosphere is made up of CO2 which has a mean molecular weight of 44 atomic mass units. Given that the lower planetary temperature is 730K, use the barometer equation to determine the scale of Venus's atmosphere (the height at which pressure drops to 1/e of the surface pressure. Take the mass and radius of Venus to be 4.8E24kg and 6050km respectively


P = Ps e^(-Mgh/RT)

I need to find h

where Ps is surface pressure. The first thing I did was find g of Venus using a gravitational equation and I got 8.75ms-2.

R and T are simple. M is problematic... Wouldn't I need the total mass of all the CO2 gas?

And I can cancel out the P and Ps because I know that P is Ps x (1/e). So the Ps cancels and I'm left with 1/e on the left side. However when I anti-log I'm left with a -1, so if I even get to finding the height it would end up being negative.

I'm doing something horrible wrong here but I don't what.

Help please.
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Dec22-09, 06:38 PM
P: 121
K so I've been a stupid boy again and I forgot the other negative on the right side. Now all I have is M to solve... How do I get M? M is the masses of the gas CO2 right? But I must have like trillions of CO2 molecules all with molecular mass 44... What do I do?
Dec22-09, 06:46 PM
P: 121
K I looked somewhere and it said the M is just the mass of the gas... so I assume that if one atomic mass is of the order 1.64E-27, then I multiply by 44.

My final answer for h is 6.37E-5m.

Is this correct? I know 1/e is a small number anyway.. but is it?

Dec23-09, 10:44 AM
P: 121
Use of the Barometer equation

Any help for this one?

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