Understanding the Power and Energy of Electrical Current and Voltage

[mysearch]

Without replicating the details, an electric current of 1 ampere flowing through a 1mm^2 copper wire appears to correspond to an electron velocity of 0.075 mm/s, i.e. electrons move slower than snails!

As a consequence, the kinetic energy associated with the moving electron charges in the wire appear to be miniscule. By considering the energy delivered per second, we would seem to be referring to power, i.e. watts, which allows a comparison with the definition P=VI. This equation suggests that the power associated with 1 ampere driven by a voltage of 100V would be 100 watts, while the power delivered by the kinetic motion of the charged electrons supporting the 1 ampere current flow appears to be virtually negligible. Therefore, I am trying to better understand the physical process of energy conversion and transfer, as a typical description of electrical current and voltage might take the following form:

- Current describes how many electrons are passing through a wire per second and, as such, high current means lots of electrons are in motion.

- Voltage describes how much energy the electrons carry, high voltage means lots of energy.

The unit of electrical current is the ampere, which resolves to charge per second (I=nq/t), where (n) is the number of free electrons carrying charge. Needless to say there can be a lot of free electrons even in 1 mm^3 of copper, but as indicated, the sum of the kinetic energy associated with even [n] electrons flowing is negligible. On the other hand, the unit of voltage (V) can indeed be resolved into energy per charge, but if the electron does not carry the energy as kinetic energy, how is this energy physically assigned to a charged electron?

Voltage (V) can also be defined in terms of an electric field (E=volts per metre), where this electric field presumably represents potential energy. For example, if I consider the electric field [E=F/q] defines a force (F) on a charge (q), there would be some expectation that this would result in a charged electron acquiring a velocity (v) and therefore kinetic energy, but this form of energy has been shown to be negligible, at least, in terms of the electron current flow. Again, in this context, it seems difficult to explain how the electrons ‘carry’ the energy/power associated with the product of (VI)?

Of course, if the current flows through the wire of an electric motor, it creates a magnetic field that causes physical rotation, which presumably represents the transfer of EM field potential energy into kinetic energy of the motor. However, the interchange between the 2 primary forms of energy, i.e. potential and kinetic, seems less obvious than that of the gravitational potential model. Therefore, I was wondering whether any members have any insight to clarify the issues raised. Thanks

 

[eljose79]

Thank you for bringing up these interesting questions about the physical process of energy conversion and transfer in electrical current and voltage. I can provide some clarification and insights on these topics.

Firstly, it is important to understand that the movement of electrons in a wire is not the only source of kinetic energy in an electrical circuit. In fact, the majority of the kinetic energy in a circuit is due to the movement of charged particles within the atoms of the conducting material. This is known as thermal motion and it is responsible for the majority of the kinetic energy in a circuit. So, while the electron velocity may seem slow, the overall kinetic energy in a circuit can still be significant.

Secondly, the concept of voltage can be a bit confusing. Voltage is a measure of electric potential difference between two points in a circuit. It is not a measure of energy carried by individual electrons. Rather, it is a measure of the potential energy that can be converted into kinetic energy when electrons move from a higher potential to a lower potential. So, when we talk about high voltage, we are referring to a large potential difference that can result in a significant amount of energy being converted into kinetic energy.

To address your question about how the energy is physically assigned to a charged electron, it is important to understand that energy is not a tangible object that can be carried by the electron. Rather, it is a measure of the ability to do work or cause a change. In the context of electricity, energy is transferred through the movement of electrons, but it is not carried by individual electrons.

Finally, the interplay between potential and kinetic energy in an electrical circuit may seem less obvious than in a gravitational potential model, but it follows the same principles. Just as an object gains kinetic energy when it falls from a higher gravitational potential to a lower one, electrons gain kinetic energy when they move from a higher electric potential to a lower one. The conversion of potential energy into kinetic energy is what allows electrical devices, such as motors, to work.

I hope this helps clarify some of the concepts and questions you have raised about electrical current and voltage. If you have any further questions, please do not hesitate to ask. As scientists, we are always happy to explain and share our knowledge with others.