Beatrice Lang
Electricity is a fundamental part of modern life, but many of us rarely consider the physical aspects of its generation, transmission, and consumption. When we flip a light switch, we expect the light to turn on, but how do we know electricity is flowing? Electricity travels in closed circuits, and when we turn on a switch, we close the circuit, allowing electricity to flow through the light and back into the wire. This movement of electrons is what we refer to as an electric current, which is defined as the net rate of flow of electric charge through a surface. In the case of our light switch, the current is created by electrons moving through the wire. These electrons originate at a power station and travel through transmission lines, substations, and distribution lines before reaching our homes.
| Characteristics | Values |
|---|---|
| Definition of Electricity Flow | The flow of charged particles, such as electrons or ions, moving through an electrical conductor or space |
| Charged Particles | Electrons, Ions |
| Conductor Types | Wire, Nanowire, Semiconductors, Electrolyte, Plasma |
| Voltage | Pressure of electricity, measured in Volts |
| Current | Flow of charge from electrons within a wire |
| Alternating Current (AC) | Electrical current generated by the power station and received at homes that continually changes direction |
| Circuit | The path on which electricity flows |
| Ammeter | Device used to measure current |
| Galvanometer | Device used to measure current, requires breaking the electrical circuit |
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What You'll Learn
Electricity is the flow of charged particles
Electricity flows in a closed circle called a circuit. When a light switch is turned on, the circuit is closed, allowing electricity to flow through the light and back into the wire. When the switch is turned off, the circuit is opened, and the electricity flow is stopped. This is why a light bulb turns off when the circuit is broken.
The charged particles that make up electric current are called charge carriers. In electric circuits, these are often electrons moving through a wire. However, in semiconductors, charge carriers can be electrons or holes, and in plasma, they are ions and electrons. The direction of the current is defined as the direction in which positive charges flow. In conductive materials, the negatively charged electrons are free to move about, while the positively charged atomic nuclei remain fixed in position.
Electric current can be measured with a device called an ammeter, and it is expressed in units of ampere, or "amp", in the International System of Units. Electric current is also known as amperage. It is a fundamental concept in understanding how electricity works and how it can be used to power our devices.
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Voltage and current
Voltage is the electrical force that would drive an electric current between two points. It is the difference in charge between two points. It is measured in volts, which is the potential energy difference between two points that will impart one joule of energy per coulomb of charge that passes through it. One volt will drive one coulomb of charge carriers, such as electrons, through a resistance of one ohm in one second. The voltmeter is used to measure voltage.
Current is the rate at which electric charge flows past a point in a circuit. It is the flow of charge from electrons within a wire. The standard unit of measurement for current is the Ampere, or Amps, and the device used to measure it is called an ammeter. The SI unit for current is Coulomb/second. One ampere of current represents one coulomb of electrical charge moving past a specific point in a circuit in one second. An electric current always produces a magnetic field. The stronger the current, the more intense the magnetic field.
To help understand the relationship between voltage and current, a common analogy is a water tank. In this analogy, the water amount represents the charge, the water pressure represents the voltage, and the water flow represents the current. The more water in the tank, the higher the charge, and the more pressure is measured at the end of the hose.
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Electricity travels in closed circuits
The movement of electrons is what we know as electricity. Electrons flow in a closed circuit, which is a complete path that allows for the continuous flow of electrical current. This is achieved through a conductor, such as a wire.
When a switch is turned on, electrons are subjected to an electric field, and all the electrons in the circuit start flowing almost simultaneously. The electric field influences the entire circuit at lightning speed, while the electrons themselves move at a snail's pace. The charges closest to the light bulb will start transforming electrical energy into light or heat.
The electrons in a circuit are pushed from the negative terminal of a battery through the bulb to the positive terminal. In a battery, one terminal has an excess of negative charges, while the other has positive charges. When a wire is connected to the battery, the electric field influences the negatively charged free electrons in the wire's atoms. The electrons are pushed by the negative terminal and pulled by the positive terminal, moving from atom to atom and creating an electric current.
Electric shocks occur when a person becomes part of an electrical circuit. This can happen when a person touches a live wire and a ground at the same time, creating a pathway for electricity to flow through their body. The severity of the shock depends on several factors, including the type and amount of current, the duration of contact, and the path the current takes through the body.
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How electricity is generated
The process of electricity generation involves converting primary sources of energy into electric power. This process is carried out in power stations or power plants. While consumable electricity is not available in nature, electricity generation involves transforming other forms of energy into electricity.
Electricity is most often generated through electromechanical generators, driven primarily by heat engines fuelled by combustion or nuclear fission. However, electricity can also be generated through other means, such as the kinetic energy of flowing water and wind, solar photovoltaics, and geothermal power.
Electric generators convert a form of energy into electricity. Most electricity generation is based on the discovery made by scientist Michael Faraday in 1831. Faraday found that moving a magnet inside a coil of wire induces an electric current to flow through the wire. This led to the design of the electromagnetic generators used today. These generators use an electromagnet, which is a magnet produced by electricity, rather than a traditional magnet.
A basic electromagnetic generator consists of a series of insulated wire coils forming a stationary cylinder, known as a stator, surrounding an electromagnetic shaft called a rotor. When the rotor turns, an electric current is generated in each section of the wire coil, with each section acting as a separate electric conductor. The currents in the individual sections then combine to form a single large current, which is the electricity that moves from generators through power lines to consumers.
Different types of turbines used in electricity generation include steam turbines, combustion (gas) turbines, hydroelectric turbines, and wind turbines. Steam turbines are the most common globally, accounting for about 42% of electricity generation in the US. Combined-cycle power plants, which may use steam turbines, combustion turbines, or internal-combustion-engine generators, supplied about 34% of US net electricity generation in 2022.
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Measuring electric current
Electric current is the flow of electric charge, and it is measured using an ammeter. The SI unit for measuring electric current is the ampere (A), which is equal to a flow of one coulomb of charge per second.
There are several methods for measuring current, but the most common approach involves performing an indirect measurement of the voltage across a precision resistor and applying Ohm's law to determine the current across the resistor. This law states that, in an electrical circuit, the current passing through a conductor between two points is directly proportional to the potential difference (voltage drop) across the two points and inversely proportional to the resistance between them. Modern ammeters are essentially voltmeters with a precision resistor, allowing for accurate and cost-effective measurements.
Another method for measuring current is based on electromagnetism and is associated with the early moving coil (d'Arsonval) meter. The d'Arsonval meter is a type of ammeter that detects and measures electric current. It is an analog electromechanical transducer that produces a rotary deflection in response to electric current flowing through its coil.
In a series circuit, an ammeter is always placed so that the electric current passes through it. This allows the ammeter to measure the current flowing through the circuit without affecting the current. The current in a series circuit remains the same everywhere, and adding a component to the circuit alters the current on both sides of the component.
Analog current loops are used when a device needs to be monitored or controlled remotely over a pair of conductors. The "4-20 mA" standard, where 4 mA represents a zero percent signal and 20 mA represents a 100 percent signal, is commonly used in industrial instrumentation and communication.
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Frequently asked questions
Electricity is the flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. When you turn on a light switch, you close the circuit, allowing electricity to flow through the light and back into the wire.
A circuit is a closed loop or circle, which electricity needs to have a complete path to flow. When you turn on a switch, the electricity is free to flow around the circuit and power your devices.
Electricity is generated in power stations, where it is sent through transformers to increase voltage. It then flows through transmission lines, carried by large towers, to substations. From there, distribution lines carry electricity to houses, businesses, and schools.
Electric current can be measured using a device called an ammeter. It can also be measured by detecting the magnetic field associated with the current without breaking the circuit.
