# What is voltage in a circuit?

What is voltage in a circuit? We just started learning about electricity in my school. From what I understand; potential is potential energy per Coulomb and voltage means difference in potential. So, if you have a battery with 4 voltage and a wire connecting the poles of the battery, does that mean electrons at the negative pole will have a potential energy of $4*q$, where $q$ is the charge of the electron? And when the electrons have reached the positive pole, all the potential energy will have been transformed?

I have a feeling I'm not understanding this concept.

• Be VERY careful with the nomenclature for this subject matter. Voltage is also known as potential difference, which is DIFFERENT than electric potential, which is DIFFERENT than electric potential energy. Using only the term "potential" is incomplete and ambiguous. – David White Mar 29 at 18:09

I think you understand it quite well.

A useful analogy for DC circuits is to imagine the electrons as water in a pipe. Voltage is like pressure so a battery is like a tank at a high level (like the water tank in the loft of a building). Current is the rate of flow (e.g., litres/second). For a given pipe diameter, the rate of flow (current) increases with the pressure (voltage). This is Ohm's Law.

Read up a bit more on this analogy and post back if you have any specific questions.

The whole story starts from electric forces. With each conservative force,we associate a potential energy. You can understand potential energy as a measure of instability for positive charge(for your understanding). We measure with respect to positive by default. So a region of positive charges has more electric potential energy (positive charge is unstable there due to repulsion). The repulsive forces cause instability which causes charges to flow from high concentration of similar charges to low concentration of similar charges. We relate the same using concept of electric potential energy. Electric charges is most analogous to gravitational systems(easy to relate) but difference comes only that charge may repel also. Instead of energy (which is different for different charges) we use potential which is same for charges(dependent on configuration of surroundings). Like we define gravitational potential at different heights on earth. The difference of potential (voltage) causes charge to flow. (Like difference of heights is required for body to fall). Coming to your question, we reference potential to be zero at infinity (assuming no charges at infinity),but for practical situation it has no significance. It is only difference of potential that matters. In case of battery 4V means positive charge at positive terminal is at higher energy by 4q than positive charge at negative terminal. (For negative charge , energy is negative which would mean it is at higher energy at negative terminal). Hence positive charge flow from positive to negative terminal through wire. The process is analogous to free fall of body. Hope this made things clear