Electricity Principals

Introduction Before we can start talking about electricity we need to be able to understand the fundamentals of the subject.

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Conductors Any material that conducts energy is known as a conductor. Most metallic elements are good conductors of electricity this is because they have ‘free’ electrons; the electron in the outer shell of the atom is able to be ‘knocked off’ when energy is added to the metal. The electron travels to the next atom where it knocks off another electron and the energy is said to flow through the material. Name materials that are good conductors of electricity?

Insulators Any material that resists the flow of energy (heat, electricity, sound, etc.) is classed as an insulator. Some materials are able to resist one form of energy whilst other materials are able to resist more than one type of energy. –E.g.glass will resist heat and electricity but not light thermo plastic will resist electricity but not heat Most non-metals resist heat and electricity to varying degrees. Name materials that are insulators of electricity?

Most metals have electrons in the outer shell of their atoms that are only loosely connected to the atom. As an electrical supply is connected to these metals the loose electron is knocked off by the EMF (Electrical Motive Force) Voltage. These electrons become free and are pushed by the voltage until they bump into the adjacent atom knocking its electron off; this continues until the voltage is turned off. Most nonmetals have electrons that are tightly bonded to the atom so they can not become ‘free’ as a result they do not conduct electricity.

Atoms Atoms are the smallest discreet building blocks of elements. They are made up of three types of sub- atomic partials protons, neutrons and electrons. The atom has two main parts the nucleus and the electron cloud. The nucleus is made up of protons and neutrons.

Atoms A proton has a positive charge. A neutron has no charge. An electron has a negative charge. Heat and electrical energy is transmitted through metals via the movement of electrons

Atoms

Voltage Voltage also known as Electro-Motive Force (EMF), is the amount of force pushing the electrons through a conductor. The unit of measurement of voltage is the Volt (V) The high the voltage the greater the force pushing on the electrons allowing them to go further.

Voltage A 9 volt battery is able to push the electrons through a conductor and lights a bulb; but it would not have enough push to force electrons through your skin and give you an electrical shock. 230V from a domestic mains is easily capable of pushing electrons through your skin and electrocuting you.

Amperes The flow of electrons pushed by the voltage is called the current; current is measured in amperes / amps (A or I) The more electrons that flow the greater the current. The amount of current that is considered lethal is between mA (0.1 to 0.2 amp) A 1.5kw kettle draws / uses 6.5 amps

Ohms As we discussed earlier conductors allow the flow of electricity; the easier the electrons can be pushed through the material the less resistance it has. The harder it is for the electrons to flow through a material the greater the resistance. Resistance is measured in Ohms (Ω)

Watts Watts are a measurement of power. Watts are calculated be multiplying the voltage by the current. We can transpose this formula to the following; –V x I = W –W ÷ V = I –W ÷ I = V

Alternating Current (A.C.) Alternating current is when the flow of electrons alternate / change direction. A.C. is the type of voltage that comes from our plug sockets. The symbol for A.C. is A.C. is described by its voltage, phase and frequency.

Sine Wave Time Amplitude (Voltage or Current) 1 Cycle

Frequency The frequency of A.C. voltage is defined as the number of cycles per second; frequency is measured in hertz Hz One full cycle per one second is one hertz The domestic voltage in this country is 50Hz the means that there are 50 full cycles per second.

Direct Current (D.C.) Direct current is when all of the electrons in the circuit flow in the same direction. The most common occurrence of D.C. is from batteries. Most micro electronics use D.C. equipment needs an inverter to rectifier the A.C. to D.C. you may come across a rectifier inside boiler controllers. The symbol of D.C. is

Basic Symbols As with plumbing the electrical industry have symbols; we do not need to know them all but there are a few that we will come across during the course of our plumbing.

Switch Earth Battery Lamp illuminator Voltmeter Diode D.C. current A.C. current Lamp indicator Ammeter Resistor Variable resistor

Parallel Parallel is when the ‘loads’ are connected to the circuit independently. Because the load has its own separate connection the voltage will remain the same across all the loads. If all of the loads are turned on at the same time the voltage will remain the same but the current will go up. Care must be taken not to overload the circuit.

Series Series is went the ‘loads’ are connected one after the other on a single circuit. This means the current flows through all of the loads. If one of the loads fail all of the power to the circuit will stop working. The voltage drops proportionally across each load; we can use ohms law to calculate the voltage drop across the loads.