Electromagnetism - Conductors and Insulators

Electromagnetism The electric charge At the base of all electrical phenomena there is a property of matter which is called an electrical charge (Q) and is measured in coulomb (C). In nature there are two types of electric charge: positive, indicated by the symbol +; negative, indicated by the symbol -. Electric charges of the same sign are repelled. Electric charges of opposite sign attract each other. The smallest electric charge is the electron: Conductors and Insulators Conductors are materials that conduct electrical current. Electric conductors are those materials that have the property of letting the electric charge propagate on its surface, thus allowing the passage of electric charge through themselves. Materials that prevent the passage of electrical current are called insulating. Electrical insulators are those materials that are electrified by rubbing only in the part of the surface where the contact occurred precisely because they do not allow the passage of charge through themselves. Examples of conductors: copper, iron, water. Examples of insulators: wood, paper, glass. Coulomb's Law Coulomb's law describes the force exerted by an electric field on an electric charge. It is the force that acts between electrically charged objects, it is defined by the value of the interaction between two point and stationary electric charges in a vacuum. The formula of Coulomb's law : F is the force (N), Q1 and Q2 are the electric charges (C), d is the distance between them (m), k is the Coulomb constant that varies from material to material. Gauss's law Gauss's law states that the flow of the electric field vector through any closed surface surface is equal to the ratio between the algebraic sum of the charges enclosed within the surface and the dielectric constant of the vacuum By algebraic sum we mean that if within the surface the total charge is zero, the flow is zero. If the sum of the charges is positive, the flow is positive, if the sum of the charges is negative, the flow is negative. Gauss's law is of considerable importance because it allows not only to deduce the charges present once the electric field is known, but also to calculate the electric field in a simple way, when the physical situation is endowed with particular symmetry. Gauss's theorem is valid not only for the electric field, but also for the gravitational one, substituting the charges for the masses. Dielectric constant When a material is placed between charged objects, the electrical force that manifests itself changes. It is maximum in vacuum and therefore any other material attenuates the force exerted between the electric charges. Relative dielectric constant: Voltage and Current If the two conductive objects are not in contact and have different electrical potential, there is a difference in potential AV between them, also called electrical voltage. An electrical generator is defined as a device capable of creating and maintaining a constant potential difference between two different points (called poles) of a conductor. An electrical current is defined as a continuous flow of electrical charges determined by a difference in potential created by a generator. Current magnitude is measured in amperes (A): Resistance The ratio between AV (potential difference) and I (current magnitude) defines the electrical resistance of each conductor, called resistance. Ohm's Law First Ohm's law: Once the temperature has been fixed, the magnitude of the electric current circulating in a conductor is directly proportional to the difference in applied potential. Conductors that comply with Ohm's law are called ohmic conductors. At a constant temperature, they have a resistance value independent of the difference in potential applied. Second Ohm's law: the electrical resistance of a conductor with a constant section is proportional to its length (I) and inversely proportional to the area (A) of the section R is the resistance, p is a constant and is called resistivity (it depends on the material the conductor is made of), I is the length of the conductor and A is the area of the conductor section