Trystan Casey
Understanding how electricity flows is fundamental to modern technology, from smartphones to kitchen appliances. Electricity is the flow of electric charge, with electrons moving from areas of negative charge to positive charge, creating an electric current. This current can be direct, flowing in one direction, or alternating, and is measured in amperes. The circuit, a closed path or loop, is essential for electricity to flow. When a switch is turned on, the circuit is complete, and electricity flows, but if the circuit is broken, the flow of electrons and current stop. This simple concept powers everything from light bulbs to complex electronic devices.
| Characteristics | Values |
|---|---|
| What is electricity? | The flow of electric charge |
| What is electric charge? | The movement of electrons through a conductor |
| What is a conductor? | A material through which electrons can move freely, e.g. metals, wires, semiconductors, insulators, vacuum |
| What is a circuit? | A closed path or loop through which electricity flows |
| What is a complete circuit? | A circuit that leads from the negative charge source, through the conductor, and back to the positive charge source |
| What is an incomplete circuit? | A circuit that is broken or interrupted, preventing the flow of electricity |
| What is voltage? | A potential difference applied across a conductor that creates an electric field |
| What is the electric field? | A force that propels electrons through the conductor |
| What is conventional current? | The arbitrarily defined direction of positive charge flow |
| What is electron flow? | The movement of negatively charged electrons, which is the actual direction of current flow |
| What is direct current (DC)? | A system with unidirectional flow, produced by batteries, thermocouples, solar cells, etc. |
| What is alternating current? | A type of current that can be converted to direct current using a rectifier |
| How is current measured? | Using an ammeter or a galvanometer (which requires breaking the circuit) |
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What You'll Learn
Electric current and its direction
Electric current is the flow of electric charge, which, in most household contexts, means the movement of electrons through a conductor. These electrons move from areas of negative charge to areas of positive charge, creating an electric current. In conductive materials, such as metals, some electrons are free to move. These electrons aren't bound to any particular atom and can drift from one atom to another.
The direction of electric current is from the positive terminal to the negative terminal, which is known as "conventional current". This definition was created before scientists knew that electrons, which carry a negative charge, were the charges actually moving. In reality, the current flows from the negative terminal to the positive terminal, which is known as "electron flow". Despite this discrepancy, both models are appropriate and describe how circuits behave.
The conventional model of current flowing from positive to negative is useful for understanding how circuits work. When a voltage or potential difference is applied across a conductor, it creates an electric field. This field exerts a force on the free electrons, propelling them through the conductor. For electrons to flow, there must be a complete path or circuit, leading from the negative charge source, through the conductor, and back to the positive charge source.
The water pipe analogy can help illustrate the concept of electric current and its direction. Similar to how pressure is applied to one end of a pipe to force water to flow in one direction, electromotive force or voltage is applied to a conductor to create an electric field that channels electrons in a particular direction. The amount of water flow is proportional to the pressure, just as the amount of current is proportional to the voltage.
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Voltage and electric fields
Electric fields and voltage are fundamental concepts in physics, and understanding them can help us identify and predict the flow of electricity.
Electric fields are vector fields that originate from electric charges and time-varying electric currents. They are present at every point in space, and their strength is defined by the force exerted on a small stationary test charge at that point, divided by the charge. The SI unit for measuring electric fields is the volt per meter (V/m), which is equivalent to the newton per coulomb (N/C). The electric field is stronger closer to charged objects and weaker farther away, and it acts between two charges in a similar manner to how the gravitational field acts between two masses.
Visualising electric field lines can help illustrate their properties. These lines always start from positive charges and end at negative charges, never crossing or closing in on themselves. The density of these lines on a diagram represents the strength of the electric field.
Voltage, or electric potential difference, is the change in electric potential energy per unit charge. It is measured in joules per coulomb, which is equivalent to a volt. Voltage represents the energy change per charge and does not depend on the charge itself.
To illustrate the relationship between electric fields and voltage, consider an example with a constant electric field. The electric field's magnitude can be determined concerning the change in electric potential. This relationship is analogous to a ball on a hill; the ball's acceleration down the hill depends on the steepness of the hill.
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Electron movement in circuits
The movement of electrons through a circuit is called electric current or current flow. This movement of electrons is what we refer to as electricity.
In conductive materials, such as metals, some electrons are free to move. These electrons are not bound to any particular atom and can drift from one atom to another. Electrons move from areas of high concentration to areas of low concentration, creating an electric current. This movement can be compared to the flow of water down a hill.
To understand electron movement in a circuit, it is essential to know the basics of electricity flow. Electricity flows when there is a complete path or circuit. The circuit must lead from the negative charge source, through the conductor, and back to the positive charge source. For example, in a simple setup with a light bulb, a battery, a switch, and a wire, closing the switch completes the circuit. The battery's negative terminal repels electrons, sending them through the wire to the bulb, lighting it up. The electrons then continue flowing back to the positive terminal.
The movement of electrons in a circuit is influenced by the electric field created by applying a voltage or potential difference across the conductor. This electric field exerts a force on the free electrons, propelling them through the conductor. The magnetic field lines represent the direction of force on a positive charge, influencing the movement of electrons.
It is important to note that the term "current" in electronics can have two meanings. Firstly, it refers to the flow of electrons through a conductor, indicating the movement of the negative charge carried by the electrons. Secondly, it specifies the volume or number of electrons moving past a point in the circuit at a given time, determining the quantity of electrons in motion.
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Circuit diagrams
An electric cell is represented by a long and short parallel line, with the long line indicating the positive terminal and the short line representing the negative terminal. A battery, which consists of multiple electric cells connected together, is represented by two or more electric cell symbols arranged in series. The positive terminal of one cell is connected to the negative terminal of the next. When two wires cross each other in a circuit diagram without a dot or circle at the intersection, it means that the wires do not make electrical contact and are simply crossing paths without connecting.
A switch is represented by a line with a gap or break in it. When the switch is closed or turned on, the gap is bridged, indicating the flow of current. When the switch is open or turned off, the gap remains, indicating the interruption of the current flow. A wire joint is indicated by a dot or a small circle where two or more wires intersect or connect, signifying an electrical connection at that point. A resistor is represented by a zigzag line and is used to limit the flow of electric current in a circuit. A variable resistor, also known as a rheostat or potentiometer, is represented by a resistor symbol with an arrow or diagonal line passing through it, indicating that the resistance value can be adjusted.
An electric bulb or lamp is represented by a circle with a cross inside it, with the cross signifying the filament or light-emitting part of the bulb. An inductor, a passive component that stores energy in the form of a magnetic field, is represented by a coil-shaped symbol. It consists of several loops or turns of wire. A capacitor, used to store electrical charge, is represented by a pair of parallel lines with another line bisecting them.
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Types of circuits: series and parallel
The flow of electricity is the movement of electric charge, which, in most household contexts, means the movement of electrons through a conductor. Electrons move from areas of negative charge to areas of positive charge, creating an electric current. In conductive materials, such as metals, some electrons are free to move from one atom to another.
When there are two or more electrical devices in a circuit with an energy source, there are two basic ways to connect them: in series or in parallel.
Series Circuits
In a series circuit, all components are connected end-to-end, forming a single path for the current to flow. The current that flows through each of the components is the same, and the voltage across the circuit is the sum of the individual voltage drops across each component. The total resistance in a series circuit is equal to the sum of the individual resistances. Series circuits are sometimes referred to as "current-coupled" or "voltage dividers".
Parallel Circuits
In a parallel circuit, all components are connected across each other, forming exactly two electrically common nodes with the same voltage across each component. There are multiple paths for the current to flow, and the total current is the sum of the currents flowing through each component. Parallel circuits are also known as "current dividers".
Both types of circuits are important for powering and controlling appliances. For example, in homes and offices, parallel circuits are used to power appliances, while series circuits control the power.
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Frequently asked questions
Electricity is the flow of electric charge, which, in most household contexts, means the movement of electrons through a conductor.
Electricity flows through a complete path or circuit. The circuit must lead from the negative charge source, through the conductor, and back to the positive charge source.
A conductor is a material through which electricity can flow. Metals are conductive materials, and in them, some electrons are free to move from atom to atom.
A circuit is the closed path on which electricity flows. It is a circle that must be complete for electricity to flow.
