School of PE Blog

The modern world runs on electricity; every day, we use it to power our homes, charge our devices, and light up our streets, but have you ever wondered what exactly electricity is? Simply put, electricity is the phenomenon resulting from the movement of an electric charge. Together in this blog, we will explore the history of electric charge's discovery, what it is, and the fundamental principles that govern it.

The very first instance of electric charge can be traced back to the ancient Greeks. They first noted that rubbing certain materials together, such as fur and amber, would cause them to attract or repel one another. Later, in the 1700s, American scientist Benjamin Franklin conducted his own series of experiments that led him to coin the usage of positive and negative charges. He added that electricity was not generated but transferred from one material to the other (Freedman et al., 2012, 688).

In 1897, British physicist J.J. Thompson, through his experiments using cathode ray tubes, discovered the electron. A cathode ray tube (CRT) is an electronic device that was once widely used in television sets, computer monitors, and other outdated electronic devices. Inside these CRTs was an electron gun that produced a beam of electrons accelerated by an electric field toward a fluorescent screen (University of Oxford, n.d.). The discovery of the electron revolutionized the field of physics; it explained how electricity is generated and established the foundation for the development of future electronics.

Electric charge is an intrinsic property of matter, which serves as a fundamental attribute that defines the interaction and behavior of objects in the presence of electric fields. Electric charge quantifies the amount of electrical energy an object holds, playing a crucial role in various aspects of our lives. The unit of measurement of an electric charge is Coulomb (C), named after French physicist Charles-Augustin de Coulomb.

From his own experiment, Benjamin Franklin observed that objects that had gained electrons were negatively charged, while objects that had lost electrons had a positive charge. Electric charges, whether positive or negative, can interact with one another. Much like a magnet, when two charges of the same polarity - either positive or negative - are brought near one another, they will repel each other. However, when two charges of opposite types are brought near each other, they will attract each other and try to come together (Freedman et al., 2012, 688).

Electric charge can be visualized as a property that exists on the surface of an object. This property can be either positive or negative. The charge is distributed across the surface of the object and can be calculated using the following equation (Boston University, 1999):

Q = ne (1)

Where Q is the electric charge, n is the number of electrons, and e is the charge of a single electron.

There are two fundamental universal principles that govern electric charge: the principle of conservation of energy and the principle of conservation of charge.

1. Principle of Conservation of Energy

The principle of conservation of energy states that energy can neither be created nor destroyed, but it can be converted from one form to another (University of Calgary, n.d.).

Using a simple closed-loop circuit, a battery connected to a lightbulb, we can visualize the conservation of energy. The chemical energy stored in the battery is then converted into electrical energy, which flows through the circuit and is converted into light and heat energy by the light bulb. Throughout the entire process, the total energy of the system remained constant. Thus, no energy was created nor destroyed; rather, it was transformed from one form to another.

2. Principle of Conservation of Charge

The principle of conservation of charge states that the total amount of electric charge in a closed system is constant (Freedman et al., 2012, 690).

When two neutrally charged objects, such as a plastic rod and a piece of fur, are rubbed together, they can become charged. In this instance, the rod gains a negative charge while the fur gains an equal amount of positive charge. This means that the total amount of electric charge in the system remains constant. The charge is transferred from one body to another and not created or destroyed. This principle of conservation of charge is believed to be a fundamental law of nature, and it has never been observed to be violated. Even in high-energy interactions where particles are created and destroyed, such as the creation of electron-positron pairs, the total charge of a closed system remains constant.

To illustrate both the principle of conservation of energy and conservation of charge, we can consider the example of a battery connected to a light bulb. When the circuit is closed, a flow of electrons occurs in the wire connecting the battery to the bulb, causing the bulb to light up. During this process, the battery converts chemical energy into electrical energy, which is transferred to the bulb as an electric charge. However, the total amount of charge in the circuit remains constant, meaning that the amount of charge leaving the battery is equal to the amount of charge arriving at the bulb. When the circuit is opened, the flow of electrons stops, and the energy is stored in the electric field created by the separation of charges in the wire and battery.

Electric charge is a fundamental property of matter that has revolutionized our understanding of electricity and electronics. The principle of conservation of electric charge, which states that the total amount of charge in an isolated system remains constant, is closely related to the principle of conservation of energy, and both principles play a crucial role in our understanding of the behavior of electricity. These principles have enabled us to develop devices such as batteries, light bulbs, and transistors that have transformed our lives.

Ready to supercharge your studies in electrical engineering? Check out School of PE's FE Electrical and PE Electrical exam prep courses now! We look forward to supporting your success.

Boston University. (1999, July 6). Electric charge and Coulomb's law. Physics. Retrieved May 14, 2023, from http://physics.bu.edu/~duffy/py106/Charge.html

Freedman, R. A., Ford, A. L., & Young, H. D. (2012). Sears and Zemansky's University Physics: With Modern Physics (A. L. Ford, Ed.). Addison-Wesley.

University of Calgary. (n.d.). Law of conservation of energy. Energy Education. Retrieved May 14, 2023, from https://energyeducation.ca/encyclopedia/Law_of_conservation_of_energy

University of Oxford. (n.d.). Cathode ray tube. Oxford Department of Physics. Retrieved May 14, 2023, from https://www2.physics.ox.ac.uk/accelerate/resources/demonstrations/cathode-ray-tube