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 electrical 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 repel 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
SCIENCE: ELECTRICITY & MAGNETISM
CEIP Santa Ana. Madridejos
1.3.- ELECTRICAL CIRCUIT. An electrical circuit is an interconnection of some electrical elements where electrical charges can flow. All appliances work because they have electrical circuits. Elements of a circuit are: .- Power source gives energy to the circuit. A battery, a dynamo or a generator that converts mechanical energy to electrical energy. .- Conductors are metallic wires, made of copper generally. .- Load devices transform electricity in light(bulb), sound (radio, MP3), heat, movement… .- Control devices, like a switch. Protection devices, like a fuse.
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Electricity flows through a closed circuit. Every electron goes from the negative electrode to the positive one. When the circuit is closed, the electricity flows, when the circuit is open, there isn’t any flow of energy. The switch opens or closes the circuit. . .
1.4.- ELECTRICITY AT HOME. In houses, power also flows through electrical circuits, but we can’t see wires because they are inside the walls. Power source is from the nearest power station. Electricity comes through cables from the station, and in every house there is an electric meter that controls the amount of energy consumed at that house. There are some fuses to protect all devices like bulbs, appliances… Electricity is very dangerous, so it’s very important to be careful with it, and take some precautions: .- Don’t touch damaged wires or insert objects into sockets. .- Don’t pull to unplug wires. .- Don’t plug lots of devices in the same socket.. .- Don’t manipulate electrical devices if you are wet…
SCIENCE: ELECTRICITY & MAGNETISM
CEIP Santa Ana. Madridejos
2.- MAGNETISM. Magnetism is the property of some substances to attract some metals. The bodies that have got this property are called magnets. There are two types of magnets: .- Natural magnets: attract iron and other metals by their own composition: magnetite. .- Artificial magnets: attract some metals by the influence of other magnets ( touch, or friction), or by an electrical current. 2.1.- PROPERTIES OF MAGNETS. A magnet has two poles, north pole and south pole, with intense forces of attraction. Poles with different name attract each other but poles with the same name repel each other.
Magnetic field is the space surrounding a magnet or an electrical current that has a magnetic influence inside it. There are magnetic forces that attract or repel parts of other magnets or pieces of some metals inside this space. If a magnet breaks itself, its poles don’t separate in each new parts, but they form new smaller magnets with both poles. Lines of force in a magnetic field. 2.2.- EARTH’S MAGNETIC FIELD. The geomagnetic field is the magnetic field generated by the motion of molten iron alloys in the core of Earth. So our planet works like an enormous magnet. Geographical poles and magnetic poles on Earth are near each other but they don’t totally fit. Magnetic poles can have variations, and even they change their polarities through the pass of time. A compass is an instrument that points at the Earth’s magnetic poles. It is used for orientation and navigation. Geomagnetic field is used by animals to guide and navigate (homing pigeons, migratory birds, turtles…). This field also protects our planet from some types of radiations from the Sun, and space.
Turtles can navigate using geomagnetic field.
Geomagnetic field protects our planet from radiations.
SCIENCE: ELECTRICITY & MAGNETISM
CEIP Santa Ana. Madridejos
2.3.- ELECTRICITY AND MAGNETISM. Electricity and magnetism are two types of energy that can be easily transformed one into the other. Electrical current creates magnetic fields. An Electromagnet is formed by a wire rolled around a piece of iron (it is called solenoid) , that works as a magnet when the electrical current goes through it.. They are used in buzzers, loudspeakers, microphones, industry (electromagnet cranes)‌
Homemade electromagnet
Electromagnet crane
Electric motors transform electric energy (through an electromagnet which is spinning by the attraction and repelling forces with another magnet) into movement.
ELECTRICITY
MAGNETISM
MOVEMENT
Electric motor diagram
Electromagnetic induction consists of generation of electrical energy from a changing magnetic field. If an induction coil (that is a wire rolled around a piece of iron) moving near a magnet, produces a flow of electrons (an electrical current). This is the reason because generators and dynamos produce electricity.
Diagram of a generator
MOVEMENT
MAGNETISM
ELECTRICITY
SCIENCE: ELECTRICITY & MAGNETISM
CEIP Santa Ana. Madridejos
GLOSARY-VOCABULARY: interaction: interacción
electrical charge: carga eléctrica
property: propiedad
neutral: neutro
uncharged: sin carga
to gain: ganar
to lose: perder
positive ions: iones positivos
negatively: negativamente
friction: rozamiento
repel to each other: se repelen uno al otro
woolen jumper: jersey de lana
near enough: suficientemente cerca
to transfer: transferir, enviar
electromagnetic field: campo electromagnético
current: corriente
electrode: electrodo
electron cloud: nube de electrons
copper: cobre
insulator: aislante
to flow: fluir
interconection: interconexión
electric potencial diference: diferencia de potencial eléctrico
appliance: electrodoméstico
wire: cable
power source: fuente de energía
load device: aparato que consume energía
switch: interruptor
fuse: fusible
electric meter: contador eléctrico
amount: cantidad
damaged wires: cables estropeados socket: enchufe de pared
to plug: enchufar
to manipulate: manipular
wet: mojado
magnet: imán
to attrack: atraer
to repel: repeler
magnetic field: campo magnético
but: pero, sino…
motion: movimiento
each other: uno del otro
molten iron alloys: aleaciones fundidas de hierro
totally fit: coinciden totalmente
even: incluso
polarity: polaridad through the pass of time: a través del tiempo
compass: brújula
to navigate: navegar
migratory birds: aves migratorias
radiation: radiación
easily: fácilmente
electromagnet: electroimán
solenoid: solenoide
buzzer: timbre
loudspeaker: altavoz
crane: grúa
homemade: casero
to spin: girar
induction coil: bobina de inducción
homing pigeon: paloma mensajera