Does a rechargeable battery weigh more when it charged than when it's not? When charged, it's full of electrons, which are energy, but energy =mass (*c^2, of course). So the difference might be tiny but IS there a difference?
p.s. or is there some kind of weird electro-gravity thing going and it actually weighs less!?
2007-07-27 00:39:41 · 4 answers · asked by AmigaJoe 3 in Science & Mathematics ➔ Physics
Crap! I would have realized that if I'd thought about it a little more. I guess I was thinking more about something like a capacitor. Leyden jar? Something like that?
2007-07-27 00:48:35 · update #1
Assuming you're talking about a "sealed" system, then yes, the charged battery weighs more.
As explained by another post, this has nothing to do with the overall number of electrons, which does not change as a battery discharges. The energy within the battery is stored in terms of chemical energy, the details of which depend on the type of battery
However, the formula E=mc^2 applies irrespective of the means by which the energy is stored, giving the difference in weight as m=E/c^2. So your typical mobile phone battery with stored energy around 10,000 Joules weighs around 1/10th of a nanogram more than when it is fully discharged.
Aside: If you can't be bothered to do the calculation yourself, google will happily do it for you:
http://www.google.co.uk/search?hl=en&q=10000+joules+in+grams
2007-07-27 02:17:37 · answer #1 · answered by ponxx 1 · 1⤊ 0⤋
No, it weighs exactly the same. And the electrons don't actually leave the battery or just disappear, they go from one end to the other, that's how a battery works. Also, electrons, for all practical purposes, weigh ALMOST nothing, even compared to neutrons and protons. Basically all a recharging battery does is reverses the process so they can be used again.
Oh, and that e=mc^2 only applies to 100% conversion of mass into energy. Electrons aren't being converted into pure energy, it's the flow of the electrons that is creating the energy. So this equation does not even apply.
2007-07-27 07:45:10 · answer #2 · answered by Anonymous · 2⤊ 0⤋
Yes, you could have worked it out yourself but you got a very good answer and you should reward that answer with 10 points.
2007-07-27 07:52:30 · answer #3 · answered by Swamy 7 · 0⤊ 0⤋
You are not God, i.e. you cannot create mass nor destroy it.
2007-07-27 09:27:03 · answer #4 · answered by ? 6 · 0⤊ 0⤋