Current flows from positive to negative, while electrons (which actually carry the charge) flow from negative to positive. Current flow is determined by the number of electrons passing through a cross-section of a conductor in one second.
Understanding Current Flow
Current is a measure of the rate of electrical charge flow past a point in a circuit. More specifically, it represents the amount of charge passing through a given cross-sectional area of a conductor per unit time.
Conventional Current vs. Electron Flow
It's crucial to understand the distinction between conventional current and electron flow:
- Conventional Current: Defined as the flow of positive charge, moving from the positive terminal to the negative terminal of a circuit. This is the established convention used in circuit analysis.
- Electron Flow: The actual movement of electrons, which are negatively charged particles. Electrons flow from the negative terminal to the positive terminal.
While electron flow is the physical reality, conventional current is the standard model used in electrical engineering and physics.
Measuring Current
Current is measured in amperes (often shortened to "amps"), with the symbol "A". One ampere is defined as one coulomb of charge passing a point in one second.
| Unit | Symbol | Description |
|---|---|---|
| Ampere | A | Unit of electric current |
| Coulomb | C | Unit of electric charge |
| Second | s | Unit of time |
For example, if 6.24 x 1018 electrons (one coulomb of charge) pass a point in a wire in one second, the current is one ampere.
Factors Affecting Current Flow
Several factors influence the magnitude of current flowing in a circuit:
- Voltage: Higher voltage generally leads to a higher current (given constant resistance)
- Resistance: Higher resistance restricts the flow of current.
- The number of charge carriers: the amount of free electrons.
- The drift velocity: the average speed of electrons due to the electric field.
Practical Insights and Examples
Consider a simple circuit with a battery and a resistor.
- The battery provides the voltage (electrical potential difference) that drives the current.
- Electrons flow from the negative terminal of the battery, through the resistor, and back to the positive terminal.
- Conventional current is depicted as flowing from positive to negative, even though electrons are moving in the opposite direction.
- Increasing the resistance of the resistor will decrease the current, while increasing the battery's voltage will increase the current.
