SCIENCE: ELECTRICITY & MAGNETISM
CEIP Santa Ana. Madridejos
1.- ELECTRICITY. Electricity is a kind of energy produced by movement and interaction between electric charges (positive and negative). Every substance or body have electric charges (because of the atoms that form the substance), but not all substances show electric properties. 1.1.- ELECTRIC CHARGE. All kind of matter is formed by atoms. Atoms have two parts: .- Nucleus formed by protons (positive electric charge), and neutrons with no charge at all. .- Electron Shell (or electron cloud) formed by electrons (negative electric charge). Atoms usually have the same number of protons and electrons, they are neutral or uncharged (with no charge), but they can gain or lose electrons: .- If atoms lose electrons, atoms become positive ions (+). The substance or body is positively charged. Structure of atoms .- If atoms gain electrons, atoms become negative ions (-). The substance or body is negatively charged. Substances with the same electric charge repell to each other. Substances with different electric charge attract to each other. We can charge electrically a body by friction. A plastic pen frictioned against a woollen jumper or our hair, can attract small pieces of paper when they are near enough (if they are inside its electromagnetic field). This is because electrons from wool have been transferred to the pen and it is negatively charged. 1.2.- ELECTRIC CURRENT. Electric current is the flow of electrons from atom to atom through a conductor (from one atom’s electron cloud to another atom’s electron cloud). Electrons move from negative electrode (anode) to positive electrode (cathode).
Electrons’ movement makes electric current
We can classify substances in two groups: .- Conductors are substances that permit electric current moves through them. Metals like copper and aluminium are good conductors because their electrons can move easily. .- Insulators are substances that don’t permit the movement of electric current. Electrons from their atoms can’t move easily, like wood, rubber… We need some items to have an electric current: a.- Electric charges that can move (electrons). b.- Conductor substances where electrons can flow. c.- A generator that produces enough energy to maintain the electric potential difference between two points (two poles) and makes electrons move. Insulators
Conductors