Electricity in Circuits


Written by Travis M. Moore
Last edited 1-Jun-2020


What is Electricity?

Simply put, electricity is the movement of electrons from one atom to another. That's it. When you flip a light switch, a connection is made between two wires (full of atoms), and the electrons hop from one atom to the next, "pushed" from a power source toward the light bulb (see Figure 1).

FIG. 1. © Kaiser Science

Let's get a little more specific. Hydrogen, the most basic atom, consists of one proton and one electron. It's important to keep in mind that protons have a positive charge and electrons have a negative charge. So a single hydrogen atom really has no charge: the proton and electron cancel each other out. The overly simplistic Bohr model of a hydrogen atom is shown below (Figure 2). Note how the electron orbits the proton.

Bohr model of hydrogen atom
FIG. 2. © Travis M. Moore (2020).

In simple terms, the electron is bound to the proton by electrostatic force. That boils down to the conventional wisdom that "opposites attract." Just like magnets (hence the "-magnetic" in electromagnetic), a positive and negative charge will attract each other, while similar charges (i.e., two positive charges / two protons; or two negative charges / two electrons) will repell each other.

That said, some atoms hold on to their electrons more strongly than others. We see the difference in materials that conduct electricity well (conductors) and materials that conduct electricity poorly (insulators). For example, copper wire is well-known for its ability to conduct electricity and is used in countless electronics applications. Copper is a conductor. You can then assume, correctly, that the electrons in copper atoms are easily removed. Why can we assume this? Remember the definition of electricity above; it's really nothing more than the movement of electrons. So atoms that have electrons that are easy to move conduct electricity well. The electrons in a piece of wood (an insulator) are held tightly to the atom, and as you may know, wood doesn't conduct electricity very well at all.

How is electricity so fast?

Electromagnetic energy travels at nearly the speed of light. That's why even if a light switch is nowhere near the light bulb, the light bulb still turns on immediately after flipping the switch. There is a simple explanation for how this happens. The movement of electrons through atoms is similar in concept to pushing marbles through a pipe (Figure 3).

marbles in a tube
FIG. 3. © Travis M. Moore (2020)

If the pipe only fits four marbles, adding another marble to the front of the pipe will force the last marble out. Each marble only moves over one space (or atom), but because all the marbles (electrons) move when one is added at the beginning, it doesn't really matter how far away the end of the pipe (wire) is because the very last marble is pushed out. This concept is illustrated in Figure 4, which shows a piece of copper wire. The center is zoomed in so we can see the actual atoms.

FIG. 4. © Travis M. Moore (2020).

Test Your Understanding

Electricity is the movement (flow) of electrons.
A conductor is any material that accommodates the flow of electricity. Examples include many metals (e.g., platinum, gold, copper), and ocean water.
An insulator is any material that resists the flow of electricity. Examples include rubber, dry wood, and the air.
The electrons of conductors can easily leave the atom, while the opposite is true of the electrons of insulators.
When a power source adds an electron, the others move over to accommodate it. So adding an electron at the beginning of a wire has an almost immediate effect at the end of the wire.


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