Electricity

ELECTRICITY Manuel Calleja DESIGN & TECHNOLOGY DEPARTMENT Manuel Calleja

DESIGN & TECHNOLOGY DEPARTMENT

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History: Electrical phenomena have been studied since antiquity, though advances in the science were not made until the seventeenth and eighteenth centuries during the “Second Industrial Revolution” when engineers were able to put it to industrial and residential use. Two people with an special meaning were: ●

Thomas Alva Edison: He was an American inventor and businessman.

He developed many devices that greatly influenced life around the world, including the phonograph, the motion picture camera, and a long-lasting, incandescent light bulb. In 1882 Edison switched on the world's first large-scale electrical supply network that provided 110 volts direct current to fifty-nine customers in lower Manhattan.

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Nikola Tesla: He was a Serbian-American inventor, mechanical engineer, and electrical engineer. He was an important contributor to the birth of commercial electricity, and is best known for developing the modern alternating current (AC) electrical supply system. (He invented the AC motor and generator.

Manuel Calleja

DESIGN & TECHNOLOGY DEPARTMENT

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Electric current: Atoms are made of three smaller parts neutrons (with no charge), and equal numbers of + charged protons ( Both are in the nucleus and oppositely-charged external cloud or shells of electrons.

The electrons in the shells closest to the nucleus have a strong force of attraction to the protons.

Sometimes, the electrons in the outermost shells do not. These electrons can be pushed out of their orbits. Applying a force can make them move from one atom to another. These moving electrons are electricity.

Manuel Calleja

DESIGN & TECHNOLOGY DEPARTMENT

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Methods of generating electricity The fundamental methods of directly transforming other forms of energy into electrical energy are: •

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Static electricity, from the physical separation and transport of charge (examples: triboelectric effect and lightning) Electromagnetic induction, where an electrical generator, dynamo or alternator transforms kinetic energy (energy of motion) into electricity, this is most used form for generating electricity, it is based on Faraday's law, can be experimented by simply rotating a magnet within closed loop of a conducting material (e.g Copper wire) Electrochemistry, the direct transformation of chemical energy into electricity, as in a battery, fuel cell or nerve impulse.

Photoelectric effect, the transformation of light into electrical energy, as in solar cells Thermoelectric effect, direct conversion of temperature differences to electricity, as in thermocouples.

Piezoelectric effect, the internal generation of electrical charge resulting from an applied mechanical force •

Manuel Calleja

DESIGN & TECHNOLOGY DEPARTMENT

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Effects of Electricity Heating: 'The heating effect of electric current is used in many everyday devices. Electric cookers, kettles and toasters are among the household appliances that rely on it.

Joule’s Law states that the rate at which heat is produced in a resistor is proportional to the square of the current flowing through it, if the resistance is constant.

Chemical: Passing an electric current through a liquid causes chemical changes in a process called electrolysis.

Electroplating uses electrolysis to put a layer of one metal on top of another.

Examples include chromium plating of bathroom and car parts, and silver plating of cutlery and jewellery.

Magnetic Electric current passing through a wire generates a magnetic field around the wire.

This effect is used in all sorts of ways. Examples include electric motors and electromagnets. In a car, for example, the central locking uses electromagnets called solenoids to operate the lock mechanism.

Another widespread example is the loudspeaker, where variations in the magnetic effect of an electric current are translated into sound waves that we can hear.

Manuel Calleja

DESIGN & TECHNOLOGY DEPARTMENT

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Main Electrical quantities: Electric current: a movement or flow of electrically charged particles, typically measured in amperes (A) using an Ammeter.

Electric voltage: the capacity of an electric field to do work on an electric charge, typically measured in volts (V) using a voltmeter.

Electric resistance is the ability of a substance to resist the flowing of the current, typically measured in Ohms (立) using an Ohmmeter.

Electric power: Is the electrical energy per time that is provided commercially, by the electrical power industry.

To measure the main electric multimeter or a multi-tester, also known as a VOM (Volt-Ohm meter), is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current and resistance.

Ohm's Law: Ohm's Law shows the relationship between the voltage (V), current (I) and resistance (R).

V = I.R Manuel Calleja

Ohm's law triangle

DESIGN & TECHNOLOGY DEPARTMENT

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Electrical circuits Components of an electrical circuit or electronic circuit can be connected in many different ways. The two simplest of these are called series and parallel and occur very frequently. Components connected in series are connected along a single path, so the same current flows through all of the components. Components connected in parallel are connected so the same voltage is applied to each component.

A simple electrical circuit. This circuit has a power source, a complete path for electrons to flow, and a resistor as the load.

Manuel Calleja

DESIGN & TECHNOLOGY DEPARTMENT

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Series circuit All components are connected end-to-end to form only one path for electrons to flow through the circuit.

V=I*R VE1-2= V1 + V2 IE1-2= I1 = I2

In a series circuit, the current through each of the components is the same, and the voltage across the components is the sum of the voltages across each component.

RE1-2= R1 + R2

Manuel Calleja

DESIGN & TECHNOLOGY DEPARTMENT

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Parallel circuits2.00cm All components are connected between the same two sets of electrically common points, creating multiple paths for electrons to flow from one end of the battery to the other In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component.

V=I*R VE1-2= V1 = V2 IE1-2= I1 + I2 1/RE1-2= 1/R1 + 1/R2

Manuel Calleja

DESIGN & TECHNOLOGY DEPARTMENT

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Series-parallel (mixed) circuits: When the circuit components are series-connected in some parts and parallel in others, we won't be able to apply a single set of rules to every part of that circuit. Instead, we will have to identify which parts of that circuit are series and which parts are parallel, then selectively apply series and parallel rules as necessary to determine what is happening.

If we are able to identify which parts of the circuit are series and which parts are parallel, we can analyze it in stages, approaching each part one at a time, using the appropriate rules to determine the relationships of voltage, current, and resistance. The rest of this chapter will be devoted to showing you techniques for doing this.

Manuel Calleja

DESIGN & TECHNOLOGY DEPARTMENT

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Circuit diagram A circuit diagram (also known as an electrical diagram, elementary diagram, or electronic schematic) is a simplified conventional graphical representation of an electrical circuit.

The main Circuit diagram symbols are:

Manuel Calleja

DESIGN & TECHNOLOGY DEPARTMENT

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Component

Name

Function

Symbol

Primary battery Transform chemical energy to ( Cell electrical energy

Power Sources

Secondary Battery

The same but can be rechaged

Generator

Is a device that converts mechanical energy to electrical energy.

Lamp or Bulb

Transforms electricity to light

Resistor

Transforms electricity to heat.

Consumers

Control

Motor

Transforms electricity mechanic energy.

Buzzer

Transforms electricity to sound.

Switch

Is an electrical component that can break an electrical circuit

Push button switch

The contacts remain in one state unless actuated

Changeover Switch

Is an electrical componet that diverts from one conductor to another

Relay

Manuel Calleja

Electrically operated switch ( electromagnet )

DESIGN & TECHNOLOGY DEPARTMENT

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Component

Name

Ammeter

Instrument used for measuring current (series )

Voltmeter

Instrument used for measuring voltage ( parallel )

Measuring instruments

Fuse

Safety Devices

Symbol

A fuse interrupts excessive current (blows) so that further damage is prevented

an electrical circuit from damage Circuit breaker Protect caused by overload or short circuit

Residual current device

Manuel Calleja

Function

Shuts off an electric circuit when it detects that current is flowing along an unintended path

DESIGN & TECHNOLOGY DEPARTMENT

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Types of currents. ac/dc What does it mean: ac/dc? Ok, apart from a rock group?

There're two types of current, defined based on the directions of the movement of the electrons.

Direct current (DC or "continuous current") is the flow of electricity in a single direction, from the positive to the negative terminals (potential, poles).

Batteries is one of the main sources of direct current (DC), but many other sources also exist such as bridge rectifiers in power supply, solar panels, etc.

Manuel Calleja

DESIGN & TECHNOLOGY DEPARTMENT

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If an electric current in a circuit reverses direction every so often, it is called an alternating current (AC). For example, the current that flows through an domestic light bulb when connected to the mains electricity supply reverses direction 50 times every second (50 Hz) and is therefore an alternating current.

The usual waveform of an AC power circuit is a sine wave, because this leads to the most efficient transmission of energy. But in certain applications there are used different waveforms, such as triangular or square waves.

When one speaks of alternating current one mostly refers to the form in which electricity is delivered to businesses and residences. But audio and radio signals carried on electrical wire are also examples of alternating current. In these applications, an important goal is often the recovery of information encoded (or modulated) onto the AC signal.

Manuel Calleja

DESIGN & TECHNOLOGY DEPARTMENT

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