Understanding Electrical Current Flow in Circuits

Illuminated pendant lights with incandescent amber bulbs hanging at home

Supakorn Kaewinta / EyeEm / Getty Images

For most people, electricity is a mysterious force that somehow magically appears when we flip a light switch or plug in an appliance. Yet, while the science behind the flow of electricity is very complex, the basics of electrical flow, or current, are easy to understand if you learn some key terms and functions. It also helps to compare the flow of electricity through wires with the flow of water through pipes. Although the analogy is not perfect, many characteristics of electrical flow in circuit wires are similar to the flow of water in a plumbing system.

  • 01 of 05

    Moving Electrons

    Atom orbited by electrons
    Sharif Tarabay/Getty Images

    What we call electrical current occurs on the particle level among the atoms of a conducting material—in a household circuit, this the copper wiring. In each atom there are three types of particles: neutrons, protons (which carry a positive electromagnetic charge) and electrons (which carry a negative charge). The important particle here is the electron, since it has the unique characteristic of being able to separate from its atom and move to an adjacent atom. This flow of electrons is what creates electrical current—the jump of negatively-charged electrons from atom to atom.

    How Generators Work

    What sends the electrons into motion? The physics are complicated, but in essence, electrical flow in circuit wires is made possible by a utility generator (a turbine powered by wind, water, an atomic reactor, or burning fossil fuels). In 1931, Michael Faraday discovered that electrical charges were created when a material that conducts electricity (metal wire) is moved within a magnetic field. This is the principal by which modern generators work: The turbines—whether powered by falling water or steam created by nuclear reactors—rotate huge coils of metal wire inside giant magnets, thereby causing electrical charges to flow.

    With this massive electrical field of positive and negative charges established, the electrons in the wires throughout the power grid jump into action and begin to flow in cadence with the electrical field. When you flip a light switch or plug in a lamp or toaster, you are actually tapping into a large utility-wide flow of electrons being pulled and pushed by utility generators that may be hundreds of miles away.

    Electrical generators are sometimes likened to water pumps—they do not create the electricity (just like a water pump does not create water), but they make the flow of electrons possible.

  • 02 of 05

    Current = Flow of Elecricity

    Wires connected by blue sparks

     Victor De Schwanberg/Science Photo Library/Getty Images

    The term current refers to the simple flow of electrons in a circuit or electrical system. You can also liken electrical current to the quantity, or volume, of water flowing through a water pipe. Electrical current is measured in amperage or amps.

    AC vs. DC Current

    Electrical current exists in two types: alternating current (AC) and direct current (DC). Technically, DC current flows in one direction only, while AC current reverses direction. In everyday terms, AC is the form of generator-created electricity that operates lights, appliances, and outlets in your home, while DC is the form of power provided by batteries. For example, your flashlights are DC systems, while your home's outlets use an AC system.

    Many renewable energy sources such as solar and wind generators, produce DC electricity that is converted to AC for use in the home. An automobile's battery is a DC system used to start the engine, but once the engine is started, the automobile's electrical system has an alternator that begins to create AC current to run the various systems.

  • 03 of 05

    Voltage = Pressure

    Gauges in electrical plant
    Marek Jagoda / EyeEm / Getty Images

    Voltage, also known as electromotive force, is often defined as the pressure of the electrons in a system. It can be likened to the water pressure in a pipe. The standard circuits in your home carry either about 120 volts (the actual voltage can vary between about 115 to 125 volts) or 240 volts (actual range: 230 to 250 volts). Most light fixtures and outlets are fed by 120-volt circuits, while dryers, ranges, and other large appliances typically use 240-volt circuits. 

  • 04 of 05

    Wattage = Rate of Flow

    Electricity meter
    Tom Chance/Getty Images

    The term wattage refers to the rate at which electrical energy is dissipated, or consumed. The total amount of power consumed by the electrical system in your home is read through the utility company's electric meter. It is measured in kilowatt-hours or 1,000 watt-hours, and that is how you are billed.

    Each electrical device, such as a light fixture or appliance, has a rate of usage measured in watts. For example, a 100-watt light bulb burning for 10 hours uses one kilowatt-hour of electricity. 

    Amps, volts, and watts exist in a mathematical relationship to one another, expressed as follows: Watts = Volts x Amps

    If an appliance is rated at 120 volts and 10 amps, it will use up to 1,200 watts when it is running: 120 volts x 10 amps = 1,200 watts. 

    Continue to 5 of 5 below.
  • 05 of 05

    Ohms = Resistance

    An analog scale volt ohm multimeter
    Stanley K Patz/Getty Images

    Ohms are the measurement of resistance to the flow of electrons through a conductive material. The higher the resistance, the lower the flow of electrons. This resistance causes a certain amount of heat to be generated in the circuit. The reason that a hairdryer blows hot air, for example, is because of resistance in the internal wiring, which produces heat. And it is resistance in the tiny wires of an incandescent light bulb that causes it to heat up and glow with light. It is also resistance that can overheat an extension cord if it is used on an appliance that draws too much current.

    In circuit wiring, too much resistance can overload a circuit and cause an electrical fire. Because bad connections caused by things like loose screw terminals and corrosion are likely culprits, electrical connections should be checked regularly to ensure safety in an electrical system.