Eletricidade e Magnetismo - Corrente Elétrica, Resistência e Circuitos Elétricos

CONTROLO CIRCUITO RESIDENCIAL SERVIÇOS IV Great Electrical Course of Instituto Sindical de Formação ISF 70h Introductory Thematic Units Electric current Electric current Magnetic fields Electric field and electrical potential Electrical resistance Exercising and solving problems Investigate the resistance of some materials conductors and insulators Electrical circuits and electrical symbols Exercising and problems Solving and exercising electrical circuits open circuits and closed circuits Ohmic conductor Source of voltage batteries Electrical source and current scheme Electrical circuit diagram and schematic diagram Switching on or off the circuit Measuring instruments Safety assembly Working with an electrician 2 PHYSICAL PRINCIPLES OF ELECTRICITY AND MAGNETISM Electric current and electric charge Electricity is based on the existence of a fundamental quantity the electric charge which appears as a positive charge or as an opposite charge negative The basic unit of electrical charge is the Coulomb C The value of the charge of an electron or proton is 16 x 1019 C smallest conceivable charge The sum of charges in an object or system usually is zero total neutrality However it is possible to have an excess or a deficiency of electrons resulting in a net charge Electric current is a flow of electric charge The charge flow is the result of the movement of electrons in conductors in a metal the negative charges ie electrons are free to move The ampere A is the SI unit for electric current One ampere corresponds to one coulomb per second flowing through a conductor Electric charge per unit time crossing a crosssection of the conductor is electric current The current has a conventional direction defined as the direction positive charges would flow The intensity of the current is the quantity of charge transported through a crosssection per unit of time Current intensity I is given by the relation I qt I 2 A means the flow of 2 coulombs of charge per second the current must be measured by inserting an ammeter in series 21 ELECTRIC CIRCUITS Electric circuits consist of a set of elements joined together by conductors or wires to form a path for electric current A circuit can be open or closed Open circuit means the circuit is not complete so there is no current flow Closed circuit means the circuit is complete allowing current to flow The elements of the circuit include sources of electrical energy conductors resistors and measurement instruments The circuit is usually represented by an electrical diagram showing the elements and the connections between them The following symbols are commonly used in electrical diagrams Line wire Source battery Load resistor Switch Safety is important when assembling or working with electric circuits to avoid shocks Always make sure the circuit is disconnected from any power source before working on it