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Physics, Astronomy & Cosmology / How does a IR thermometer work?
« on: 30/06/2011 12:55:03 »
was just wondering...
Do IR thermometers measure the temperature of an object via the intensity or wavelengths of emitted light?
I've heard that you can measure the temperature of clouds with them, why doesn't the IR light emitted by the air in between the cloud and the detector confuse it?
[**I've heard this can damage them] What happens you point one at the sun? or an old fashioned light bulb? (is it not sensitive to visible black body radiation)?
(hopefull those make sense) thanks!
Do IR thermometers measure the temperature of an object via the intensity or wavelengths of emitted light?
I've heard that you can measure the temperature of clouds with them, why doesn't the IR light emitted by the air in between the cloud and the detector confuse it?
[**I've heard this can damage them] What happens you point one at the sun? or an old fashioned light bulb? (is it not sensitive to visible black body radiation)?
(hopefull those make sense) thanks!
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Physics, Astronomy & Cosmology / cloud in a bottle, why does alcohol work better than water?
« on: 11/05/2011 18:10:00 »
Does anyone know exactly how this works?
I searched the forum and there have been some mentions of this experiment but I still have a question
Is the result entirely down to changing temperature?
expansion > cools > vapour condenses > droplets form?
compression > heats > droplets vaporise?
You can do a similar experiment just with water but I was told a cloud requires smoke particles (from a match) to act as Cloud Condensation Nuclei (same job as silver iodide in cloud making machines).
(Description of experiment here > http://www.sep.org.uk/catalyst/articles/catalyst_21_4_484.pdf)
Is it because the change in vapour pressure is greater for alcohol?
any help much appreciated
graph done by geogebra
I searched the forum and there have been some mentions of this experiment but I still have a question
Is the result entirely down to changing temperature?
expansion > cools > vapour condenses > droplets form?
compression > heats > droplets vaporise?
You can do a similar experiment just with water but I was told a cloud requires smoke particles (from a match) to act as Cloud Condensation Nuclei (same job as silver iodide in cloud making machines).
(Description of experiment here > http://www.sep.org.uk/catalyst/articles/catalyst_21_4_484.pdf)
Is it because the change in vapour pressure is greater for alcohol?
any help much appreciated
graph done by geogebra
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Physics, Astronomy & Cosmology / how much would I weigh if there was no air?
« on: 08/03/2011 14:33:35 »
how much would i weigh (on earth) if there was no air?
I'm pretty sure you weigh less underwater because of buoyancy? so if the ocean of air was removed would I weigh more, less or the same?
thanks!
p.s. this is assuming your bloodily fluids haven't evaporated etc.
I'm pretty sure you weigh less underwater because of buoyancy? so if the ocean of air was removed would I weigh more, less or the same?
thanks!
p.s. this is assuming your bloodily fluids haven't evaporated etc.
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Physics, Astronomy & Cosmology / why does an electron beam in a cathode ray tube look blue?
« on: 17/02/2011 12:24:14 »
thanks!
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Physics, Astronomy & Cosmology / why do people wear black in the desert??
« on: 13/02/2011 15:34:19 »
someone told me that a material's colour does not effect its IR absorption/emission properties.
if so wouldn't wearing white result in you absorbing less visible light and being cooler?
or am I missing the point and its because white cloth is more expensive/not fashionable or do people mostly stay indoors during the daytime or something else?
if so wouldn't wearing white result in you absorbing less visible light and being cooler?
or am I missing the point and its because white cloth is more expensive/not fashionable or do people mostly stay indoors during the daytime or something else?
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Physics, Astronomy & Cosmology / how does this open wine bottle with shoe trick work?
« on: 18/01/2011 14:30:18 »does happen like this?
1) wine bottle accelerates towards the wall
2) the inertia of the wine makes it want to stay in the same place so it flows towards of the neck end of the bottle (air gap opens up between wine and bottom of bottle).
3) the wine and the bottle are at same speed
3) the bottle hits the wall and almost instantly stops
4) but the wine continues to flow forward (like someone in a car), hits the bottom of the bottle and rebounds, hits the cork and pushes it out a bit
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Physics, Astronomy & Cosmology / How does a magnetometer detect water?
« on: 29/12/2010 00:02:25 »
I heard the Galileo spacecraft detected signs of water in using a magnetometer, does anyone know how?
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Physics, Astronomy & Cosmology / how old is the star that created earth?
« on: 20/11/2010 02:52:38 »
one of my lecturers made the hypothesis that if U(235) and U(238) were created in the same relative abundance in supernova (which he said is quite a good assumption) you could extrapolate back to estimate when the star we are all made of exploded (and a lower bound to the age of the universe).
does this look correct? you can solve the equations algebraically but I'm a bit rusty so I just made a spreadsheet, does 8.5 to 9 billion years ago sound about right?
https://spreadsheets.google.com/ccc?key=0AntR1lCmF5GLdDc5Qnk4bV9LZHdGdlRkSG5ZRDh4Z2c&hl=en
is the earth is mainly comprised of one old star or is that a bad assumption?
I was totally amazed when he told us, and I still am, I hope there's some truth in it. Thanks.
does this look correct? you can solve the equations algebraically but I'm a bit rusty so I just made a spreadsheet, does 8.5 to 9 billion years ago sound about right?
https://spreadsheets.google.com/ccc?key=0AntR1lCmF5GLdDc5Qnk4bV9LZHdGdlRkSG5ZRDh4Z2c&hl=en
is the earth is mainly comprised of one old star or is that a bad assumption?
I was totally amazed when he told us, and I still am, I hope there's some truth in it. Thanks.
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Physics, Astronomy & Cosmology / Why do barometers use mercury rather than water?
« on: 29/09/2010 00:27:23 »
Can you use water instead of mercury in a barometer? If not, why not?
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Physics, Astronomy & Cosmology / what happens to the coolant water from a nuclear reactor?
« on: 16/08/2010 18:51:18 »
Do neutrons create many radioactive isotopes in the water (from what I remember its mostly H2O and a little bit of LiOH)?
Is it classified as low, intermediate or high level waste?
Is there much difference between the primary and secondary coolant loops?
Similar question for the water in the post reactor storage ponds thingys.
I couldn't find the answer anywhere.
Thanks
Mark
Is it classified as low, intermediate or high level waste?
Is there much difference between the primary and secondary coolant loops?
Similar question for the water in the post reactor storage ponds thingys.
I couldn't find the answer anywhere.
Thanks
Mark
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Physics, Astronomy & Cosmology / If gamma rays are so penetrating, why can our atmosphere stop them?
« on: 16/08/2010 03:27:15 »
if our atmosphere is so good at stopping gamma rays why do we need thick lead/concrete walls in nuclear reactors?
is it because 3km of gas is equivalent to a thick lead/concrete wall?
or not many gamma rays to start with compared to a nuclear reactor?
or something else?
thanks!
mark
is it because 3km of gas is equivalent to a thick lead/concrete wall?
or not many gamma rays to start with compared to a nuclear reactor?
or something else?
thanks!
mark
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Physics, Astronomy & Cosmology / If everything except water were removed from air, what would the temperature be?
« on: 05/06/2010 17:33:23 »
removing nitrogen, oxygen etc. from a volume of air at room temperature/pressure so that only water vapour remains, what will be the temperature? If it isn't above 100C why doesn't the water vapour condense?
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