I can give some partial answers based on my own models:
AC is used for transmission because transformers are ubiquitous and incredibly valuable at all stages of transmission, and transformers work using AC (you need a changing electrical field to generate a changing magnetic field). Transformers allow you to convert the voltage and isolate circuits. Isolation is important for safety, and voltage conversion is important to achieve the cross purposes of safety and efficiency. High voltage allows you to transfer more energy with fewer losses, but is far more dangerous to work with. This gets to your resistance question—resistance / heat generation are related to the amount of current and the thickness of the material. To transfer a given amount of energy, higher voltage means less current needed for the same wire, which means less heat losses.
Why 50Hz (or 60 in the US)? As far as I know, this is largely arbitrary. I do know that subtle differences in the frequency are used for signaling grid load. https://en.wikipedia.org/wiki/Utility_frequency has a lot of info though!
As for metering, I have no idea how current meters (ammeters/watt meters) work, but I am pretty sure no net electrons are entering or leaving e.g. your house or your appliance. Electrons in a circuit should be conserved, they’re just the means of transfer of energy.
Tks. You mentioned isolation is important for safety. Can you elaborate some specific examples? As per my imagination, unless the threat has been predicted then the AC transformers are useless against sudden issues. Say, an abrupt surge will still propagate via its magnetic field before we can do anything.
Isolation is not about surges, but about preventing current from flowing in a particular path at all. In a transformer, there is no conductive (only magnetic) path from the input side to the output side. So, if you touch one or more of the low-voltage output terminals of a transformer, you can’t thereby end up part of a high-voltage circuit no matter what else you’re also touching; only experience the low voltage. This is how wall-plug low voltage power supplies work. Even the ones that are using electronic switching converters (nearly all of them today) are using a transformer to provide the isolation: the line voltage AC is converted to higher frequency AC, run through a small transformer (the higher the frequency, the smaller a transformer you need for the same power) and converted back to DC.
I can give some partial answers based on my own models:
AC is used for transmission because transformers are ubiquitous and incredibly valuable at all stages of transmission, and transformers work using AC (you need a changing electrical field to generate a changing magnetic field). Transformers allow you to convert the voltage and isolate circuits. Isolation is important for safety, and voltage conversion is important to achieve the cross purposes of safety and efficiency. High voltage allows you to transfer more energy with fewer losses, but is far more dangerous to work with. This gets to your resistance question—resistance / heat generation are related to the amount of current and the thickness of the material. To transfer a given amount of energy, higher voltage means less current needed for the same wire, which means less heat losses.
Why 50Hz (or 60 in the US)? As far as I know, this is largely arbitrary. I do know that subtle differences in the frequency are used for signaling grid load. https://en.wikipedia.org/wiki/Utility_frequency has a lot of info though!
As for metering, I have no idea how current meters (ammeters/watt meters) work, but I am pretty sure no net electrons are entering or leaving e.g. your house or your appliance. Electrons in a circuit should be conserved, they’re just the means of transfer of energy.
Tks. You mentioned isolation is important for safety. Can you elaborate some specific examples? As per my imagination, unless the threat has been predicted then the AC transformers are useless against sudden issues. Say, an abrupt surge will still propagate via its magnetic field before we can do anything.
Isolation is not about surges, but about preventing current from flowing in a particular path at all. In a transformer, there is no conductive (only magnetic) path from the input side to the output side. So, if you touch one or more of the low-voltage output terminals of a transformer, you can’t thereby end up part of a high-voltage circuit no matter what else you’re also touching; only experience the low voltage. This is how wall-plug low voltage power supplies work. Even the ones that are using electronic switching converters (nearly all of them today) are using a transformer to provide the isolation: the line voltage AC is converted to higher frequency AC, run through a small transformer (the higher the frequency, the smaller a transformer you need for the same power) and converted back to DC.
Oh, I was too focused on the system function while forgetting that safety can primarily apply to human health too :)