20.1 Current
2 min read•june 18, 2024
is the lifeblood of our modern world, powering everything from smartphones to cities. It's the flow of electric charge through a , measured in amperes, and can be calculated using the formula I = ΔQ/Δt.
Understanding current is key to grasping electrical circuits and power systems. We'll explore concepts like , , and , which are fundamental to how electricity works in our daily lives.
Electric Current
Definition of electric current
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- Rate at which electric charge flows through a
- Measured in amperes (A) or coulombs per second (C/s)
- Represented by the symbol
- Directly proportional to the amount of charge flowing past a point per unit time
- , where is the change in charge and is the change in time
- in a conductor are typically electrons, but can also be positive ions (electrolytes)
- Direction of current flow depends on the type of charge carriers
- Electrons flow from negative to positive potential (battery terminals)
- Positive charge carriers flow from positive to negative potential (electrolytic cells)
- refers to the actual movement of electrons in a conductor
Concept of conventional current
- Standard direction of current flow, defined as the direction in which positive charges would flow
- Opposite to the direction of electron flow in a conductor
- In a diagram, conventional current is shown flowing from the positive terminal of a battery to the negative terminal
- Established convention before the discovery of electrons and still widely used today
- Direction of conventional current is used for analysis and calculations in most practical applications (circuit analysis)
Calculation of current using drift velocity
- () is the average velocity of charge carriers in a conductor due to an applied electric field
- Typically much smaller than the random thermal motion of electrons ( m/s)
- Current can be calculated using drift velocity and the cross-sectional area of the conductor
- , where:
- is the number of charge carriers per unit volume
- is the charge of each carrier
- is the cross-sectional area perpendicular to the direction of current flow
- is the drift velocity
- , where:
- For a given current, a larger cross-sectional area results in a lower drift velocity
- Drift velocity is usually on the order of millimeters per second in conductors (copper wire)
Electrical Properties and Ohm's Law
- is the electrical potential difference between two points in a circuit
- is the opposition to current flow in a conductor
- Ohm's law relates current, voltage, and resistance:
- Circuits are closed paths through which can flow
- Conductors are materials that allow easy flow of electric current
- Insulators are materials that strongly resist the flow of electric current
Key Terms to Review (22)
$I = \frac{\Delta Q}{\Delta t}$: The equation $I = \frac{\Delta Q}{\Delta t}$ defines the concept of electric current, which is the rate of flow of electric charge through a given cross-section of a conductor. The term $\Delta Q$ represents the change in electric charge, and $\Delta t$ represents the change in time, so the ratio of these two quantities gives the electric current, denoted by the symbol $I$.
$I = nqAv_d$: $I = nqAv_d$ is an equation that describes the relationship between current, the number of charge carriers, the charge of each carrier, the cross-sectional area, and the drift velocity of the charge carriers in a conductor. This equation is fundamental to understanding the concept of electric current and how it flows through a material.
$v_d = \frac{I}{nqA}$: $v_d = \frac{I}{nqA}$ is a fundamental equation in physics that describes the drift velocity of charge carriers, such as electrons or holes, in an electric current. It relates the drift velocity ($v_d$) to the current (I), the charge carrier concentration (n), the elementary charge (q), and the cross-sectional area (A) of the conductor.
This equation is particularly relevant in the context of understanding the nature of electric current and the behavior of charge carriers within a conductor. It provides insights into the underlying mechanisms that govern the flow of electric charge and how various factors influence the overall current.
$v_d$: $v_d$ is the drift velocity, which is the average velocity at which charge carriers, such as electrons or holes, move through a material under the influence of an applied electric field. It is a fundamental concept in the understanding of current flow in electrical circuits and devices.
Ampere: An ampere (A) is the unit of electric current in the International System of Units (SI). It represents the flow of one coulomb of charge per second.
Ampere: The ampere (symbol: A) is the base unit of electric current in the International System of Units (SI). It is defined as the constant flow of one coulomb of electrical charge per second, and it is a fundamental quantity used to describe the movement of electric charge.
Charge Carriers: Charge carriers are the mobile, electrically charged particles that are responsible for the flow of electric current in a material. These charge carriers can be either positively or negatively charged and are the fundamental building blocks of electrical phenomena.
Circuit: A circuit is a closed loop that allows the flow of electric current. It consists of various electrical components, such as power sources, conductors, switches, and loads, connected together to form a complete path for the movement of electric charges.
Conductor: A conductor is a material that allows the free flow of electric charge, typically electrons. Conductors are essential in creating electric circuits and are usually made from metals like copper or aluminum.
Conductor: A conductor is a material that allows the free flow of electric charge, enabling the transmission of electrical current. This term is crucial in understanding various topics in physics, including heat transfer methods, electric fields, electric current, and resistance.
Conventional Current: Conventional current is the historical model of the flow of electric charge in a circuit, which assumes that the positive charge carriers (typically electrons) move from the positive terminal of a voltage source to the negative terminal. This model is used in the analysis of electrical circuits and is the basis for Kirchhoff's Rules.
Coulomb: Coulomb is the fundamental unit of electric charge, named after the French physicist Charles-Augustin de Coulomb. It is a measure of the amount of electric charge and is a crucial concept in understanding various topics in electricity and magnetism, such as static electricity, electric fields, electric potential, and the behavior of charged particles.
Coulomb force: Coulomb force, also known as the electrostatic force, is the force of attraction or repulsion between two charged particles. It follows an inverse-square law and is governed by Coulomb's law.
Drift velocity: Drift velocity is the average velocity at which free charge carriers, such as electrons, move through a conductor under the influence of an electric field. It is typically much smaller than the speed of individual electrons due to frequent collisions within the material.
Drift Velocity: Drift velocity is the average velocity at which charge carriers, such as electrons or holes, move through a material under the influence of an applied electric field. It is a fundamental concept in understanding the flow of electric current and the behavior of electrical devices.
Electric current: Electric current is the flow of electric charge through a conductor. It is measured in amperes (A) and represented by the symbol 'I'.
Electric Current: Electric current is the flow of electric charge through a conductive material, such as a wire or a semiconductor. It is a fundamental concept in the study of electricity and is essential for understanding various electrical phenomena and applications.
Electrical Resistance: Electrical resistance is the measure of the opposition to the flow of electric current in an electrical circuit. It determines how much the circuit impedes the passage of electric charge, which is crucial for understanding and analyzing the behavior of electrical systems.
Electron Flow: Electron flow refers to the movement of electrons through a conductive material, such as a metal wire or semiconductor, driven by an applied potential difference or voltage. This flow of electrons is the fundamental basis for the concept of electric current and is essential to understanding the behavior of electrical circuits and devices.
Insulator: An insulator is a material that does not conduct electricity or heat well, making it essential for preventing energy loss and maintaining safety in electrical systems. Insulators resist the flow of electric current and thermal energy, which is crucial for a variety of applications ranging from household appliances to high-voltage power lines. Their ability to inhibit the transfer of energy helps maintain controlled environments and protects sensitive components from damage.
Ohm's Law: Ohm's law is a fundamental principle in electrical engineering that describes the relationship between the voltage, current, and resistance in an electrical circuit. It states that the current flowing through a conductor is directly proportional to the voltage applied across it, and inversely proportional to the resistance of the conductor.
Voltage: Voltage, also known as potential difference, is the electrical potential energy difference between two points in an electrical circuit. It is the driving force that causes the flow of electric current, and it is measured in units of volts (V).