# Puzzled about direct current and charge (flux)

• daviddeakin
In summary, the conversation discusses the concept of current and its relationship to flux or charge in a circuit. It is explained that while the current may continue to flow, the charge at a given point does not necessarily keep growing indefinitely. The potential in the circuit would eventually become too large to continue the flow of current. It is clarified that the charge that has passed a point can accumulate indefinitely.
daviddeakin
This is a question that has kept me awake, trying to rationalise it:

Current is rate-of-change-of-flux (or charge if you prefer, which is the same thing):
i = dQ/dt
Therefore, flux or charge is the time integral of the current.
Q = ∫i dt

Therefore, if you have a direct current, does this not imply that the flux/charge at a given point in the circuit keeps on growing indefinitely??

daviddeakin said:
Therefore, if you have a direct current, does this not imply that the flux/charge at a given point in the circuit keeps on growing indefinitely??
No. The current in a circuit is the rate at which charge is flowing past a surface (or point).

daviddeakin said:
This is a question that has kept me awake, trying to rationalise it:

Current is rate-of-change-of-flux (or charge if you prefer, which is the same thing):
i = dQ/dt
Therefore, flux or charge is the time integral of the current.
Q = ∫i dt

Therefore, if you have a direct current, does this not imply that the flux/charge at a given point in the circuit keeps on growing indefinitely??

And how long could you keep this current flowing into a single point? The potential would pretty soon get so large that you couldn't continue. You are mis-interpreting the Maths.

Ah, so my mistake was to say "the charge at a given point", when it should be "the charge that has passed a point", which of course can accumulate indefinitely!

Thank you for your question. It is understandable that the relationship between current and flux/charge may seem puzzling at first. Let me try to provide some clarification.

Firstly, it is important to understand that current is the flow of electric charge through a circuit. This flow of charge can be either direct or alternating. In direct current, the flow of charge is in one direction only, while in alternating current, the flow of charge changes direction periodically.

Now, when we talk about flux, we are referring to the amount of electric field passing through a given area. This flux can also be either direct or alternating, depending on the type of current flowing. So, in the case of direct current, the flux remains constant as the charge flows in one direction only. However, in alternating current, the flux changes direction along with the flow of charge.

Now, let's address your question about the flux/charge growing indefinitely in a direct current circuit. It is true that the flux/charge will continue to increase as long as the current is flowing, but there are other factors at play that limit this growth. For example, the resistance of the circuit will cause the current to decrease over time, which will in turn limit the growth of the flux/charge.

Additionally, the circuit may have components such as capacitors or inductors that can store and release charge, causing fluctuations in the current and flux. Overall, the growth of flux/charge in a direct current circuit is not infinite and is limited by other factors in the circuit.

I hope this explanation helps to clarify the relationship between current and flux/charge in a direct current circuit. If you have any further questions or concerns, please feel free to reach out. As scientists, it is our job to continue to question and explore these concepts in order to deepen our understanding.

## 1. What is direct current?

Direct current (DC) is a type of electric current that flows in one direction, unlike alternating current (AC) which periodically reverses direction. It is commonly used in electronic devices and power transmission systems.

## 2. How is direct current produced?

Direct current is produced by converting AC current through a process called rectification, which uses diodes to eliminate the negative portion of the AC waveform, resulting in a constant flow of current in one direction.

## 3. What is charge (flux)?

In physics, charge (flux) refers to the amount of electric charge passing through a given area over a given time. It is measured in coulombs per second and is used to describe the flow of electric current.

## 4. How does direct current affect electrical devices?

Direct current is commonly used in electronic devices because it provides a steady flow of current, making it easier to regulate and control. It is also less likely to cause interference with other electronic devices compared to alternating current.

The main advantage of direct current is its reliability and stability, making it ideal for use in electronic devices. However, it is not suitable for long-distance power transmission and requires specialized equipment for conversion between AC and DC. It also has limited applications in household and commercial settings.

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