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At Oxford, a Battery That's Lasted 175 Years -- So Far
sarahnaomi writes There sits, in the Clarendon Laboratory at Oxford University, a bell that has been ringing, nonstop, for at least 175 years. It's powered by a single battery that was installed in 1840. Researchers would love to know what the battery is made of, but they are afraid that opening the bell would ruin an experiment to see how long it will last. The bell's clapper oscillates back and forth constantly and quickly, meaning the Oxford Electric Bell, as it's called, has rung roughly 10 billion times, according to the university. It's made of what's called a "dry pile," which is one of the first electric batteries. Dry piles were invented by a guy named Giuseppe Zamboni (no relation to the ice resurfacing company) in the early 1800s. They use alternating discs of silver, zinc, sulfur, and other materials to generate low currents of electricity.
From The Fucking Article
"You'd think it'd be annoying as hell for a bell to be going off, constantly, for 175 years—but the voltage left in the battery is so low that the human ear can't actually hear the ringing. Instead, the clapper oscillates back and forth between the bell constantly, which you can see happening in this video. At this point, the experiment is more of a curiosity than anything—Croft says that the battery pulls 1 nanoAmp each time it oscillates between the bell’s sides, which is an exceedingly low amount of energy."
Actually the janitor changes it once a week when he cleans the room.
At the current estimated power draw, thats only (1 nanoampere) * 175 years = 0.00153401723 ampere hours. It's a long time: impressive durability, but not really amazing capacity. Laptop batteries are often ~1000 times that. I don't know the voltage here, so I can't do energy comparisons, just total amp hours.
http://en.wikipedia.org/wiki/N...
The Karpen Pile, currently on display at the Dimitrie Leonida National Technical Museum in Bucharest, Romania, still gives out 1V after 60 years.
This one has a glass enclosure so it can be studied.
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Let's put this in perspective. The only "amazing" thing here is simply that the chemicals used in the battery are very stable. The amount of energy we're talking about is very, very low.
FTA, it takes around 1 nanoampere to ring the bell once. It rings around around 2 Hz. Thus it takes 2 nanoampere a second, which works out to 7200 nanoampere-hours.
So let's see how long a AA battery could run that bell. The better AAs produce 3 amp-hour of power. That is 3000000000 nanoamperes. 3000000000 / 7200 gives us 416,666 hours, which is 47.56 years. So if we could somehow spread the power of a AA out over time so the chemicals didn't break down, it could power that bell for 47.56 years. A single D battery has 12 amp-hours of power (4 times that of a AA), thus it could run the bell for 190 years.
We're not talking about much power whatsoever - simply that the chemicals and construction of the battery are such that it has not degraded that much just through time alone.
Better known as 318230.
I'm sure Chuck Berry would agree that is an awfully long time to be playing with your ding-a-ling!
Deep space tends to be very cold
This is misleading at best.
Space in itself is a near vacuum, which (a) has no temperature of its own, and (b) is a wonderful insulator. Which is why a thermos uses vacuum for insulation.
Objects in space can become very cold over long time spans, as heat slowly radiates away without being replenished at the same rate. But space itself doesn't cool them down.
Voyager 1, which is the operative craft that's been in service the longest and receives the least amount of heat from the sun is, after most of the heaters have been turned off to conserve energy, running at around -80C temperatures. That's a veritable furnace compared to other older objects in space that have radiated away more heat over much longer time.
Also, you say "chemical batteries". Well, yes, it is, but this is a dry battery. The composition doesn't change with colder temperatures, unlike wet batteries where liquids freeze. Dry batteries don't have that problem, which is why it is interesting.
Space may be a wonderful insulator, but the flip side to that is that there's nothing to reflect back your own heat. Radiative cooling can happen very quickly. This is why a desert can go from 100F to near freezing in a matter of hours when the Earth rotates and the desert is radiating heat out into space.
There's a reason why a vacuum flask (aka thermos) is silvered--it reflects radiation. A vacuum flask is silvered on the _inside_ (including the vacuum-facing walls) as well as the outside, otherwise any contents warmer than ambient temperature would radiate their heat much faster through the flask walls.
This is why a desert can go from 100F to near freezing in a matter of hours when the Earth rotates and the desert is radiating heat out into space.
Deserts are not vacuums. Deserts cool down at night mainly through air convection. High altitude air on the planet's night side is less buoyant, and is replaced by warmer air from lower altitudes, and this process repeats all the way down to the surface. Katabatic winds are often a result, which the California "sundowner" winds is a good example of.
Needless to say, that isn't much of a concern for the microclimates of spacecraft.
Actually photons don't have a temperature as such. Sometimes you'll hear people talking about "300K light" - but it's not that the photons themselves have a temperature, but that they have an energy distribution approximating that of a black body radiator at 300K. Photons can impart energy when absorbed, which may rapidly thermalize, or they can carry away thermal energy, but they themselves don't obey the normal temperature laws. Heat only flows form higher temperature to lower temperature; however, a 3K object can radiate thermal energy as photons which will be absorbed by a 3000K object without problems - the net heat transfer is in the other direction only because the 3000K object is simultaneously radiating far more energy back at the 3K object.
Consider what exactly heat means - it's the average kinetic ("vibrational") energy of the atoms in an object. On the atomic scale temperature = speed. The essence of heat transfer by conduction is that when two atoms at different speeds collide, the slower atom speeds up, while the faster atom slows down. (the opposite rarely happens because it require that the faster atom be "rear-ended" by the slower one - only possible in very specific "T-bone" collisions") For photons that doesn't happen - they are *always* traveling faster than the atom they hit (at exactly c), and can either speed up or slow down the atom based on the angle of impact.
Now I'm curious... A question for someone better versed than I on the subject: Is is known what exactly the physical mechanism is by which kinetic energy causes photons to be emitted? The discussions I found all basically just said "it's a property of matter", which is great if you just want to characterize black-body radiation, but doesn't exactly quench my curiosity. I'm thinking it's probably related to the atomic impacts/oscillations within a sample, and that a single atom can't meaningfully be said to have a temperature as it is completely at rest within it's own reference frame.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
I don't think that's true. On a cloudy but windy night in the desert it doesn't get nearly as cold as on a clear windless night all other things being equal. In fact when I searched for "Desert nighttime cooling" here is the first thing that came up. It basically says under clear low humidity conditions at night radiative cooling is by far the the largest reason for cooling.
> (a) has no temperature of its own, and (b) is a wonderful insulator.
Oh, my. I'm afraid that both these assumptions are overstated. The background temperature of the universe is only a few degrees Kelvin, but the "vacuum" in near Earth orbit is considerably warmer and more dense than the universe at large. It's also a very good insulator as you state, but when exposed to sun light it has to cope with roughly 2 Watts/square inch of solar radiation. Even left to itself, in the shadow of some astronomical body, it will continue to cool from 'black body radiation', even if it is white or reflective.
The effects may be much more insulating than planetside environments, but these kinds of factors do affect space craft power supplies.
Deserts cool down at night mainly through air convection
So where are those supplies of near-freezing air around desert areas ?
That is true as far as it goes, but in a sufficiently large, flat desert you don't have much winds, and dry air has much lower specific heat, so it can't conduct heat away from surfaces nearly as fast as moist air. Nevertheless desert nights are usually much colder than you would expect.
What's special about deserts in this regard is that same dry air also means the atmosphere is much more transparent to infrared than, so that far more of the thermal energy radiated towards the sky by the soil escapes from the Earth entirely, rather than being reflected back to the surface. It's basically the exact opposite of the "cloud blanket" effect where dense clouds that blow in near dusk can keep it from cooling off much overnight because the greatly elevated water levels in the clouds reflect much more of the radiated heat. (obviously the effect is much less pronounced in coastal deserts where the air is heavy with moisture even if it rarely rains.)
We actually had a post here several weeks back of a new surface designed to harness the effect for cooling anywhere at any time of day: it was highly reflective over the high-energy solar spectrum, and tuned to radiate thermal energy at a specific frequency at which the atmosphere was almost perfectly transparent. More primitive technology such as coolth cells work like an inverse solar heater - heat is radiated away from a thermal reservoir overnight, and the cold water used to chill the air during the day.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
Photons are "merely" localized changes in an electromagnetic field. Intuitively, "bumping" a charged particle will cause it to wiggle, causing just such changes to propagate. This is sort of a lie depending on your intuition for "bump", but it's close enough for a 3am /. post.
It's caused by something expanding, but it's not a gas. At least mine isn't.
Confucius say, "Find worm in apple - bad. Find half a worm - worse."
The previous posters are correct - the clear, low humidity air over deserts is more transparent to infrared light and radiative loss is the major reason for fast cooling at night. I've spent the night out in the Sahara. When the air cools off and you dig into the sand you realize that not only is the sand a decent insulator, just below the surface it's also much warmer than the air.