The weight of capacitance :-)

Now charge it and reweigh! Mikek

I'm envious of your .001 division scale.

Is that charged or discharged? Charged caps weigh more.

We have a cute little scale a little smaller than a credit card. We use it for mixing tiny batches of epoxy. The resolution on yours is nice.

--

John Larkin Highland Technology Inc

Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators

Only a miligram last digit? Analytical chemistry scales are very excellent, typically 5 or 6 digits going down to micrograms. Besides wind currents, adsorbed moisture makes accurate measurements difficult down there!

Tim

-- Deep Friar: a very philos>> The weight of capacitance:

Check!!

On a sunny day (Sat, 13 Oct 2012 15:01:02 -0500) it happened amdx wrote in :

Interesting question, from Q= C.U = i.t you can calculate charge, or from i as electrons per second, the multiply by electron weight, but would charging a capacitor not simply remove electrons from one side and store those on the other side of the dielectricum? :-)

Its cheap, ebay nr 400216793091 12$50

An analogous question is: Is a full harddisk heavier than an empty one?

From that we can then derive is an empty mind lighter than a learned one?

..... which is equivalent to 111uF/kg - not a very high capacitance to weight ratio!

Yes, but the stored energy, 1/2 CV^2, has an implied mass m=e/c^2. Google has the answer: ((1 nanofarad) * 10 (volt^2)) / (c^2) = 1.11265006 × 10-25 kilograms

On a sunny day (Sun, 14 Oct 2012 10:35:44 -0500) it happened JOF wrote in :

Cool, beyond my little scale though :-)

m=e/c^2 only applies to mass/energy being converted between mass and energy, not ... "rest mass" of a capacitative charge....

Don't forget buoyancy in air.

Suppose you have a perfectly reflecting sphere into which you inject some light. The light keeps bouncing around inside forever. Does the sphere-and-cavity system gain mass when it contains light versus dark?

Actually, it doesn't matter if the sphere is perfectly reflective; if it absorbs light, it just heats up, the change in thermal energy being equal to the amount of light absorbed. Heat being phonons, which are massless, like photons, but carried in lattices rather than EM fields.

The question "which is heavier, 1 kg of matter at 100C or 1 kg of matter at 0C" is ambiguous because 1 kg could be RME or total. The actual difference is a few atoms' mass out of 10^23 or so.

If an object contains energy, it gets heavier, regardless of the form that energy is in. The most extreme example is a black hole, which swallows everything (Hawking radiation excepted) and converts it to apparent mass. It doesn't matter if swallowed photons are converted to matter at some point, the gravitational field gets more intense.

It seems to follow that photons *do* have an infinnetessimal gravitational field, corresponding to their momentum only (remember, actual mass = RME + p^2*c^4), which should make a classical black hole indistinguishable from a photon of, oh let's say 10^70 eV or so. Not sure how velocity is resolved in that case; obviously black holes aren't known to travel at c, but that's only necessary of a photon's local space-time, which is compressed inside the singularity. Probably in this case, thinking of photons and general relativity as separate models is no longer effective and there is a more conclusive model which can be derived if one were so inclined.

Tim

A charged cap should not weigh more as it's not "full" of more electrons. You can't remove the charge from a cap without moving it from one electrode to the other. They're not like water balloons where to empty it you drain the water, and it never returns the balloon and it sits there empty.

e = m * c^2

Stored energy has mass.

Irrelevant, because

Indeed.

Well, it would be very slightly hotter, which means it still has a little more energy. And real capacitors have dielectric absorption. But discounting those, no difference whatsoever.

Tim

Hard to pull charged plates apart too.

How nuch does a mole of photons weigh?

So how many farads in a black hole? :) IMO, when we use the term "weight", we're sorta invoking the image of using a balance beam* of infinite precision to weigh the thing at rest on Earth at some known radial distance from the center of the Earth.

The irony, 'course, being until you specify how it is to be measured, why, we can't even *talk* about it, really. And "rest" is a futile idea....

... from which I am sure a "farad equivalent" can be derived....

Not sure how velocity is

Photons have no mass, because they are real energy, not stored/potential energy.

Nope. Different units.