Does “electricty” or whatever it’s called that goes into your electric vehicle battery, have mass or weigh anything? My car has a 100KW battery. Is the weight substantially different when it has 0 charge versus when it is fully charged? It seems like a lot of energy goes into the battery, it must add to the net mass of the vehicle?
In: Technology
A lot of wrong answers here.
A lithium battery is made of 2 layers; when charged up one of those layers is “missing” a ton of electrons, and the other has a ton of “extra” ones. If electrons can move between the two layers, they’ll naturally do so, until they’ve pretty much equalized. You can visualize this a lot like water flowing from a higher up bucket to a lower one, until the water level is the same in both. We keep the layers mostly separate, and only allow those electrons to flow from A to B through some metal wires, and they do useful work while they’re moving. Think, a man-made channel between bodies of water, that we put a waterwheel in. When the electrons have equalized, there’s no more force to move them and the battery is dead.
Charging the battery involves pushing those electrons back into one layer, using energy to do so. Like pumping water back into the higher bucket. So, energy was used to move things, no matter was added to the system.
…That said, according to general (or special, idk) relativity, energy isn’t just able to turn into matter, energy itself has mass. The water raised up higher against gravity *literally* weighs a tiny, tiny amount more than it did before. A spring literally weighs a little more when it’s compressed. And the electrons in a battery have just a little more mass when they have that electromagnetic potential energy waiting to be spent. It’s just so little that the most accurate scales on Earth couldn’t measure the difference.
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