Electrostatics and Electromagnetism: Basic Concepts
Electrostatic Induction
Electrostatic induction is a method used to charge a conductor without putting it into contact with an electrified object.
Coulomb’s Law
Using a torsion balance, Coulomb found that the force of attraction or repulsion between two point charges (charged bodies whose dimensions are negligible compared with the distance r that separates them) is inversely proportional to the square of the distance between them.
Electric Field Flux
The electric flux is related to the force of attraction or repulsion between two point charges. Using a torsion balance, Coulomb found that this force is inversely proportional to the square of the distance that separates them.
Point Load
A point load refers to the mutual electric force that arises between two very small loads separated by a relatively large distance in relation to their sizes.
Electrification by Friction
When a body is rubbed vigorously with a cloth, it becomes positively or negatively charged, depending on its tendency to lose or gain electrons, respectively. For example, by rubbing a glass rod, it becomes positively charged.
Electrification by Contact
When a charged body is brought into contact with another, the electrical charge is distributed between the two. Thus, both bodies are charged with the same type of charge.
Electrification by Induction
An electrically charged body can attract another body that is neutral. When an electrical body is brought closer to a neutral body, an electrical interaction is established between the charges of the first and the neutral body.
Electric Potential
Electric potential at a point in an electric field is the work required to transport a unit of charge from outside the field to that point.
Gauss’s Law
Gauss’s Law relates the electric flux through a closed surface and the electric charge enclosed within that surface. It also relates the divergence of the electric field with the charge density.
Capacitor
A capacitor is a device for storing charge and electricity. It consists of two flat and parallel metal elements separated by an insulator.
Capacitance
Capacitance is a property associated with each capacitor and measures its ability to store electric charge. Capacitance is a general concept that applies when two adjacent conductive objects, separated by a non-conducting material, acquire charges of equal magnitude and opposite sign.
Electricity
Electricity is a flow of electrical charges. The moving electric charges can be of different types, depending on the environment where they travel.
Electric Field
An electric field is a region of space where electric forces act.
Magnetic Field
A magnetic field is a region in space where magnetic forces act.
Circuit Elements
- Node: A branch point where two or more currents converge.
- Branches or Conductors: The portions between consecutive nodes where the same current flows.
- Mesh: The portion of a closed circuit that starts and ends at the same node.
Electricity
Electricity is a flow of charges, although it is usual to relate electric current to conducting materials. In metals, these are electrons, elementary particles that are easily induced to move under the influence of an electric field.
Effects of Electricity
- Lighting Effects: When current flows through a conductive element, it leads to increased temperature, which in turn leads to the production of visible light (e.g., light bulbs).
- Heat Effects: With the exception of conductors at very low temperatures, the passage of electric charges generates heat in a conductive material (e.g., irons, toasters).
- Thermoelectricity: When large amounts of heat are available, electricity can be obtained through the use of steam plants. Heat is used to generate steam, which in turn spins a turbine. The turbine drives a generator to produce electricity.
- Piezoelectricity: Some non-conductive materials have the property of producing a voltage between their surfaces when mechanical stress is applied. Pierre Curie discovered this in 1883.
Types of Electric Current
- Direct Current (DC): When charges flow in a conductor, they do so under the influence of the force generated by an electric field. If the field is uniform, the magnitude and direction remain constant inside the conductor.
- Variable Current: A current created by an electric field that varies with time. In this case, the flow of charge depends on the value of the electric field at every instant.
Kirchhoff’s Laws
- Kirchhoff’s First Law: The algebraic sum of the currents at a node is zero.
- Kirchhoff’s Second Law: The algebraic sum of the voltages in any closed circuit loop is zero.