Electrical Systems

Electrical Systems Meaning

Firstly, let's define what exactly we mean by an electrical system.

This may seem vague at first, but electrical systems is a label that can encompass a wide variety of different day-to-day objects. Phones, computers, and electrical power grids are all electrical systems. The two quantities that we will always see across any type of electrical system are current and voltage, which allows for electrical energy to be generated.

When we picture electrons, we typically think of very small circular objects orbiting the nucleus of an atom in uniform motion. In reality, if we consider the electrons in a piece of metal, they are flying around in a random motion at extremely high speeds. However, current in a system only flows when there is an overall net motion of the electrons rather than just their random motion.

We have this net flow of electrons due to the difference in electrical potential, or a voltage between two ends of a wire. This is similar to the phenomenon of osmosis. If we had a solution of water mixed with salt, connected to another solution of just pure water, separated by a thin permeable barrier, the difference in salt concentrations would force the salty solution to diffuse over into the pure water solution. Similarly with electrons, if the two ends of a wire had different potential differences, this would force electrons on one end to move over to the other end, generating a current. Thus we can define voltage as the following.

Parts of an Electrical System

Now that we have established what we mean by an electrical system, let's consider the different parts that make up these systems.

Resistor

First, let's look at resistors; these electrical components have a quality called resistance. We can define resistance as the following.

All materials carry some sort of resistance. However, when we consider electrical circuits in the future, we will assume that components such as wires, ammeters, and voltmeters have zero resistance unless otherwise stated. The equation used to calculate the resistance of a resistor is

\[ R = \frac{V}{I} ,\]

where \(R\) is the resistance measured in ohms \(\Omega\), \(V\) is the voltage across the electrical components measured in volts \(\mathrm{V}\), and \(I\) is the current running across the component measured in amperes \(\mathrm{A}\). This equation is also referred to as Ohm's law.

Fig. 2 - When drawing electrical circuits, resistors are represented as a zig-zag line.

Capacitor

Moving on, another important component of electrical systems is capacitors. These components are used to store electrical potential energy through the physical separation of opposite charges on conductive plates, which results in the formation of an electric field between the two plates.

Capacitors can come in various forms. However, the one we most often come across while studying physics is the parallel plate capacitor. Referring to the figure below, we can see that the form of a parallel plate capacitor is made up of two conducting plates with a charge magnitude \(Q\) on each plate, separated by a small distance \(d\). When a capacitor is connected to a power source, the current in the circuit creates a build-up of electrons on one side of the capacitor, creating a separation of charge.

Fig. 3 - The structure of a parallel plate capacitor.

In order to measure the amount of electrical potential energy stored in a capacitor, we define its capacitance.

We can calculate the energy stored in a capacitor as

\[ U_{\text{C}} = \frac{1}{2} Q \Delta V ,\]

where \(U_{\text{C}}\) is the energy stored in the capacitor measured in joules \(\mathrm{J}\), \(Q\) is the magnitude of the charge stored on each plate measured in coulombs \(\mathrm{C}\), and \(\Delta V\) is the potential difference across the capacitor measured in volts \(\mathrm{V}\).

Inductor

Finally, an inductor is an electrical component that uses the current in a circuit to generate a magnetic field. You may have come across the term induction in everyday objects such as an induction hob. These objects use the phenomenon of electromagnetic induction to generate heat.

An example of an electrical inductor is a transformer; these allow for large voltages from power grids to be stepped down into smaller voltages that can be used in everyday objects in households. On the other hand, the process can also be reversed to allow for smaller voltages to be stepped up into larger voltages. Thus, transformers are very useful when transporting energy across electrical systems that may require a significantly different magnitude of voltage.

Fig. 4 - The structure of a step-down transformer.

The equation for a transformer is given as

\[ \frac{V_{\text{p}}}{V_{\text{s}}} = \frac{N_{\text{p}}}{N_{\text{s}}} ,\]

where \(V_{\text{p}}\) and \(V_{\text{s}}\) are the voltage across the primary and secondary conductor respectively, measured in volts \(\mathrm{V}\). On the right-hand side, \(N_{\text{p}}\) and \(N_{\text{s}}\) are the number of turns on the primary and secondary sides respectively.

Examples of Electrical Systems

Now let's consider an example of an electrical system, a circuit in your house used to take power from the main power lines and turn on the lights in your house. We represent this in the figure below as a circuit diagram.

Fig. 5 - The step-down transformer takes electrical energy from the power grid and supplies it to the bulbs in a home.

Here we have a step-down transformer converting energy from the power grid into voltages safe for domestic use. This then acts as a power source for the three bulbs connected in a parallel orientation. Whether or not the bulbs are turned on or turned off is dependent on the switch connected to the circuit: when closed, all the bulbs will have energy supplying them, and when open, the bulbs will be turned off. This is an example of an electric system that may be found in many domestic households.

Electrical Power Systems

Finally, an electrical power system is a specific type of power system that is used to transport electrical energy and acts as a power supply to other electrical systems. We have already come across an example of an electrical power system in the form of a national power grid that is used to transport electrical energy from a power plant to domestic households across the country.

An important aspect of electrical power systems is the supply of energy that is then converted into electrical energy. Examples of energy sources include

• Fossil fuels such as coal, gas, and oil

• Wind turbines

• Nuclear power

• Solar panels

• Geothermal energy

• Hydropower energy

All of these energy sources generate energy in their own unique way. However, the conversion to electrical energy is similar across the board. Electromagnetic induction is a key factor in the conversion to electrical energy, as it allows for an electromotive force to be induced through the movement of a magnetic field. Devices called generators use the energy harnessed from these various power sources to move or rotate an electromagnet. Thus, this creates a changing magnetic field around the electromagnet, so we can retrieve electrical power when placed next to a conductor.

Solar Electricity Systems

Finally, let's look at a specific example of electrical power systems, solar electricity systems. To collect solar energy, we have photovoltaic cells that are placed in areas that experience direct sunlight. These devices are made up of the semiconductor material silicon. Due to silicon's structure, the material's electrons are bounded very weakly to their atom, making them easy to dislodge. When light is shined upon the cells, the photons comprising the light rays interact with the orbiting electrons, knocking them out of place. These free electrons then behave as a current, transporting electrical energy between the cells and into our homes.

Fig. 6 - Solar panels are examples of electrical systems.