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THE ELECTRIC CHARGE
Electric charge is a property that all objects possessand is responsable for electrical phenomena.
The electric charge ofan object is the excess or defect of electrons that it has. If an atom gains or loses electrons, it is electrically charged.
All matter is made up of atoms. These atoms are comprised of smaller particles, each of which have an electrical charge:
• Electrons, which have a negative charge and are responsible for electric forces and interactions.
• Protons, which have a positive charge.
• Neutrons, which don’t have a charge.
Protons and neutrons are located inside the nucleus and electrons outside, in the electron cloud.
In general, matter is neutral – it doesn’t have an electric charge. This means that the number of negative charges (electrons) is the same as the number of positive charges (protons). Sometimes, however, there is a movement of electrons from one material to another.
STATIC ELECTRICITY VS ELECTRIC CURRENT
It’s important to clarify the difference between static electricity and electric current:
Only the latter is used to make things work. Most of the time positive and negative charges are balanced in an object, which makes that object neutral. Static electricity is the result of an imbalance between negative and positive charges in an object, after being electrified. The charges are at rest, they aren’t moving through the electrified material.
An electric current is a continuous movement of electrons. Electrons move very rapidly but advance very slowly, chaotically and in large quantities. What is really transferred at a high speed is the electric charge.
The most significant difference between the static and current electricity is that in static electricity the charges are at rest, whereas in current electricity the electrons are moving inside the conductor.
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CONDUCTORS AND INSULATORS
A material being conductor or insulator depends on the molecular structure of matter, so while in some materials the electrons are strongly bound and don’t allow for exchange, other materials electrons detach and exchange easily. We can classify materials into two types:
• Conductors are materials that allow electric currents to pass through them. In general, all metals are good electrical conductors, especially silver and copper.
• Insulators are materials that do not allow electric currents to pass through them. Plastic, wood or ceramics are examples of insulators.
ELECTRIC CURRENT
To produce an electric current there must be an imbalance between two points of the conductor – there must be a large number of electrons at one point and none at the other. The movement of electrons stops when the charge is balanced.
For electric current to exist, two elements are needed:
• Free electrons: + nº of free electrons, + electric current.
• Potential difference: there must be a difference of energy between two points, to attract and repel the free electrons that are in those points.
The electric current can be of two types:
Direct current: It is produced by a continuous flow of charges. The electrons always move in the same direction.
Alternating current: There is a variable flow of charges. The electrons change direction alternately.
ELECTRIC CIRCUITS
An electric circuit is a set of connected components through which an electric current flows. Before learning about the individual components, you must have a clear understanding that, for the electric current to flow, the circuit must be closed, allowing the electrons to flow from one battery pole to the other; if the cable doesn’t connect both poles, the electrons cannot reach the receptor, because it’s like they won’t even bother to go out.
The basic elements of an electric circuit are:
GENERATOR: A device that produces the energy necessary for electrons to move, that is to say, for maintain an electric current. A generator has two poles: one positive, and the other negative.
Generators can be: • Batteries: They use chemical processes to generate the electric current. • Alternators or dynamos: They transform motion into an electric current. • Photovoltaic solar cells: They use energy from the Sun. • Hydrogen cells: They produce energy from oxygen in the air and hydrogen.
CONDUCTORS are the elements that join all the components of a circuit and allow the flow of the current. They can be cables or wires.
DIFFERENCE BETWEEN A CABLE AND A WIRE
Both of them are joining elements of a conductive metal and both of them are protected by an insulator coating (plastic or rubber); but, wire is a single conductive metal cord that makes a single connection, and a cable is a group of wires inside a sleeve or jacket and can be used for a multiple connection. Most people use these terms interchangeably.
RECEPTORS These components transform the electrical energy that they receive into another type of useful energy.
ELECTRIC CIRCUITS
CONTROL COMPONENTS direct or interrupt the flow of the electric current. The most common types are:
• A switch (a 2-way switch): This has two positions – one to allow the flow of electric current, the other to stop it. • A 3-way switch: This has two outputs so it communicates with two different circuits, allowing the current to go one way or the other depending on its position.
• A push button: This is similar to a 2-way switch, but it has a fixed position which changes when pressed. It returns to this position when we let it go.
PROTECTION ELEMENTS interrupt the flow of the current when it gets too high. As a result, they protect the elements from damage. They can be fuses or thermal magnetic circuit breakers.
Our houses have an electric circuit permanently embedded within their walls, so we pretty much live «inside» or «surrounded by» a big electric circuit; so it is important to be safe and know which devices keep our homes protected.
EFFECTS OF AN ELECTRIC CURRENT
The energy in an electric current has different effects on the receptors, and can be transformed into other types of energy that we can use, such as heat, light and motion.
HEAT
Electrons crash into the atoms of the material they are flowing through. Part of the energy that they are carrying is transformed into heat when these collisions happen. This is called the Joule effect. The components used to produce heat are called resistors. They are used in devices such as toasters, hair dryers and electric heaters.
LIGHT
There are several ways to produce light with electricity:
The temperature of an object increases when an electric current is passed through it. When this increase is considerable, light begins to appear. Incandescent and halogen bulbs are based on this phenomenon.
Some gases emit light when they carry an electric current. Fluorescent tubes and low-energy bulbs are based on this phenomenon.
When electricity flows through an electronic component called a light-emitting diode, it emits light. Such objects are called LEDs.
MOTION
Motors transform electrical energy into motion. They are based on the forces of attraction and repulsion between a magnet and a conductor wire. Most motors consume a lot of energy, so they aren’t very energy efficient. However, they can be used to generate electricity instead of consuming it. This is the case of the dynamo, a device using a crankshaft that generates an electric current when it spins.
ELECTRIC QUANTITIES
CHARGE
It is the amount of electricity stored in an object. It is represented by the letter Q and is measured in coulombs (C). VOLTAGE
It is the difference between the electrical energy at two points in a circuit. Voltage is represented by the letter V. In the International System of Units (SI) it is measured in volts (V). To measure voltage we use a voltmeter, which should be connected in parallel.
CURRENT
It is the number of electrons that pass through a specific point in one second (the flow of electrons at that point). Current is represented by the letter I. In SI units, it is measured in amperes or amps (A). We use an ammeter to measure the current. You connect the ammeter in series to a receptor or receptors where you want to measure the current.
RESISTANCE
It is the opposition of the components in a circuit to the flow of the electric current. Resistance is represented by the letter R. In SI units, it is measured in ohms (Ω).
POWER
The amount of electrical energy consumed or produced per second. Power is represented by the letter P. In SI units, it is measured in wats (w). E represents electrical energy and is measured in joules (J) or in kilowatt hours (kwh). T represents time (h)