ELECTRICITY: CHARGE AND ELECTRIC CURRENT ELECTRIC CHARGE ELECTRIC CURRENT ELECTRIC CIRCUIT DEFINITION AND COMPONENTS EFFECTS OF ELECTRIC CURRENT TYPES OF CIRCUITS ELECTRIC QUANTITIES VOLTAGE CURRENT RESISTANCE OHM S LAW ELECTRIC POWER RATIONAL ELECTRICITY USE
CHARGE AND ELECTRIC CURRENT: 1.1.Electric charge is a property of all objects and is responsible for all electrical phenomena. These phenomena are caused by the electrical forces of attraction and repulsion. All matter is composed of atoms. Atoms are made up of other small particles: o Electrons, which have negative charge and are responsible for electric forces and interactions. o Protons, which have positive charge. o Neutrons, which don t have charge. Two objects with the same charge repel each other. Two objects with different charge attract each other. Static electricity: the charges are at rest, they don t move through the electrified material. 1.2.Electric current is a continuous movement of electrons. Conductors are materials that allow electric current to pass through them. In general, metals are good electrical conductors, especially silver and copper. Insulators are materials that don t allow electric current to pass through them. Plastic, Wood or ceramic are examples of insulators. To produce an electric current there must be an imbalance between two points of a conductor: a large number of electrons in one point and not in the other. The movement of the electrons stops when the charge is balanced. ELECTRIC CIRCUIT: 2.1. An electric circuit is a set of connected components through which an electric current circulates. Components of an electric circuit: Generator: provides the energy necessary to move the electrons. It produces a permanent electric current. Types of generators: batteries, alternators or dynamos, photovoltaic solar cells, hydrogen cells. Receptors: components that transform electrical energy into another type of energy: heat, light, motion, sound.
Control and protection components: o Control components: stop, start or change the direction of the electric current: switch, circuit switch, push botton,, DPDT switch. o Protection components stop the current when it is too strong so that the important components of the circuir are not damaged. Representation and symbols: CELL BATTERY ALTERNATOR RESISTOR MOTOR BULB BUZZER CONNECTION SWITCH PUSH SWITCH CIRCUIT SWITCH FUSE AMMETER VOLTMETER DIODE VARIABLE RESISTOR 2.2. Effects of electric current: the energy transported by an electric current is transformed into other types of energy Heat: the Joule effect is the transformation of electric energy into heat. The components used to produce heat are called resistors. They are used in devices such as toasters, hair dryers, electric heaters, etc. Light: o The temperature of an object increases with the electrical current. When this increase is considerable, light begins to appear. Incandescent and halogen bulbs are based on this phenomenon. o Some gases emit light when them receive an electric charge. Fluorescent tubes and low-energy bulbs are based on this phenomenon. They last longer and are more efficient than incandescent bulbs. Motion: motors transform electrical energy into motion.they are based on magnetic forces
2.3. Types of circuits: Series circuits: the output of each component is connected to the input of the next one, the same current flows through all elements of the circuit Parallel circuits: the input of all the components converge at a common point, and the same happens with the outputs. The current is divided to flow through all the elements and the voltage is the same across all the components. Series-parallel combination circuit: mixed series and parallel elements appear. Series-parallel combination circuit ELECTRIC QUANTITIES: Charge, voltage, current and resistance: o The charge is the amount of electricity stored in an object. It is represented by the letter Q and is measured in coulombs ( C ): o Voltage: difference between the electrical energy at two points in a circuit. The charge always moves from the point where the energy is highest to the lowest point. If there is no voltage there is no current. Voltage is represented by the letter V and measured in volts ( V ). This is also called tension. o Current: number of electrons that pass through a specific point in one second. It is represented by the letter I and measured in amperes ( A ). o Resistance: opposition of the components of a circuit to the flow of the electric current. It is represented by the letter R and measured in ohms ( Ω ). V
Measuring instruments: o Voltmeter: measures the electrical voltage, it has to be connected in parallel. o Ammeter: measures the current, it has to be connected in series. o Multimeter (polymeter): measures different electric quantities ( V, I, R ). Electric power: the amount of energy consumed or produced by an electric circuit per unit time. Power is measured in watts (W) and Energy in joules (J): E P t Ohm s Law: proportional relationship between voltage, current and resistance: V I R Current and voltage are directly proportional for any given resistance. RATIONAL ELECTRICITY USE: Electrical energy consumption has a serious impact on the environment. There are three ways we can help to reduce this impact: improve the energy efficiency of electrical devices, reduce consumption and use renewable energy sources.