Electrical Functions - Notes

Electrical Function

• An electrical function is the role that a component plays in the control or transformation of electric current.

Power Supplies

• Power supply is the electrical function performed by any component that can generate or provide and electric current in a circuit.1. Battery2. Electrical Outlet3. Photovoltaic Cell

1. Batteries

• Batteries transform the energy from a chemical reaction into electrical energy.

• Advantages:▫ Portability

• Disadvantages:▫ Must be replaced after a certain amount of time▫ Can contaminate the environment if not disposed of properly

• Applications: mp3 players, watches, remote controls

2. Electrical Outlet

• When the prongs of an electric plug enters an outlet, contact is made with parts permanently connected to an electrical network.

• Advantages:▫ Stable & long-lasting power supply▫ Hydro-electricity creates very little greenhouse gas

• Disadvantages:▫ Appliances cannot be moved far from the wall outlet▫ Appliances stop working in the event of a power shortage

• Applications: TVs, Fridges, Computers

3. Photovoltaic Cell• Photovoltaic (solar) cells generate an electric current when

exposed to light.• Advantages:

▫ Can power equipment in isolated areas without access to power grids.

▫ Can also power portable or mobile devices▫ Do not cause greenhouse gas emissions

• Disadvantages:▫ Their operation depends on sunny conditions.▫ Very expensive

• Applications: Solar homes, solar cars, calculators

Conduction

• Conduction is the electrical function performed by any component that can transmit electric current from one part of a circuit to another.▫ Electricity is primarily conducted through wiring – usually copper.

▫ Components other than wires can also act as conductors.• Ex: two pieces of metal that come into contact• Ex: the human body

Printed Circuits

• A printed circuit is an electrical circuit printed on a solid support called a circuit board.

• Printed circuits have replaced copper wires for the purposes of conduction in smaller electronic devices such as cell phones and MP3 players.

• A printed circuit is usually a plastic board 1mm thick covered in a thin layer of copper. The circuit board is then etched and finally all the excess copper is removed leaving only the electrical circuit printed on the board.

Insulation

• Insulation is the electrical function performed by any component that prevents an electric current from flowing.

• Insulators are poor conductors so they prevent electrons from leaving wires.

• Plastics & ceramics make for good insulators.

Control

• Control is the electrical function performed by any component that can open and close a circuit.▫ Switches act as controls.

Closed Circuit• A closed circuit is a circuit in which electric current flows in

a loop.

The light bulb is ON!

Open Circuit• An open circuit is a circuit in which electric current cannot flow

in a loop.

The light bulb is OFF!

Types of Switches

• Switches are categorized according to the number of contacts they can make at one time and how many possible paths electrons can follow.

• A single pole switch is one where the switch can only make one contact at a time

• A double pole switch can make two contacts at a time

Types of Switches

• Circuits where electrons flow in only ONE path have switches referred to as single-throw.

• Circuits where electrons can flow in one of two paths have switches referred to as double-throw. ▫ The position of the double-throw switch determines the path that

the electrons will take.

SwitchNumber of contacts

opened or closed at one

time

Number of possible

paths

Diagram

Single – pole,Single – throw 1 1

Single – pole,double– throw 1 2

Double– pole,Single – throw 2 1

Double– pole,Double– throw 2 2

Single pole – double throw

Double pole – single throw

Double pole – Double throw

Types of Switches• Types can take many forms.

Push-button Switch

Rocker Switch

Toggle Switch

Magnetic Contact Switch

Protection

• Protection is the electrical function performed by any component that can automatically cut current flow in the event of a power surge.

• If a short circuit or electrical overload occurs, in order to avoid serious accidents like fires or shocks and to avoid damaging plugged in appliances, protective devices such as fuses or breakers can be connected to the electrical circuits.

Fuses

• The electric current crosses the fuse through a conductive filament.

• If the current intensity exceeds a certain level, the filament melts and breaks, preventing the current from flowing through the fuse.

• The fuse then needs to be replaced.

Breakers

• In some breakers, the current passes through a bimetallic strip. Other breakers use an electromagnetic mechanism.

• When the current intensity exceeds a certain level, the strip becomes hot, it bends, and the connection is interrupted.

• In order to restore circuit operation, the breaker switch must be switched back. The breaker does NOT need to be replaced.

Resistance• A resistor is a component designed to limit the flow of electrons

through an electrical circuit.

• A resistor acts like a small-diameter pipe in a water supply system. Even if a large volume of water is present, the water flow will be restricted by the size of the small pipe. Resistors function in a similar way, by hindering the flow of electrons through a circuit.

Resistance

• Electrical resistance is expressed in ohms – [Ω]

• Ex: Resistor ‘A’ has an electrical resistance of 2500Ω.

Resistance• Resistance is usually indicated with a color code.

▫ The color of the first band corresponds to the first digit.▫ The color of the second band corresponds to the second

digit.▫ The color of the third band corresponds to the multiplier

(x 10__)▫ The color of the fourth band corresponds to the tolerance.

(+ __ )

DIGIT 0 1 2 3 4 5 6 7 8 9 Gold Silver

MULTIPLIE

R

1 101 102 103 104 105 106 107 108 109

TOLERANC

E

±

20%

± 1% ±

2%

± 5% ± 10%

COLOR BLACK BROWN RED ORANG

E

YELLOW GREEN BLUE VIOLET GREY WHITE GOLD SILVER

THE COLOR CODE FOR ELECTRICAL RESISTORS:

Resistor colour code example:

Green blue yellow gold

56 x 10 000 Ω + 5% or56 x 104 Ω + 5% or560 k Ω + 5%

What is the value of the resistor below?

41 x 105 ±10%

Transformation of Energy

• The transformation of energy is the electrical function performed by any component that can convert electrical energy into another form of energy.

• Energy is the ability to do work or effect change.• Takes many forms • Usually measured in joules (J)

Forms of EnergyType of Energy Description Examples of Sources

Elastic Energy stored in an object due to its compression or extension

• compressed spring• Stretched elastic

Electrical Energy from the ordered movement of electrons

• battery

Thermal Energy from random motion of particles in a substance

• heating element•Fire

Radiant/Light Energy found in and carried by electromagnetic waves

• light bulb microwave Sun • cellphone Fire radio/tv

Chemical Energy stored in molecular bonds • food•fuel

Wind Energy from the movement of air • wind

Sound Energy found in and carried by sound waves

• music

Hydraulic Energy from the movement of water • Waterfall

Nuclear Energy stored in the nucleus of an atom • Sun

Transformation of Energy

▫ Electrical energy can be converted into:• Radiant/light Energy → Incandescent Light Bulbs• Thermal Energy → Heating Elements• Mechanical Energy → Piezoelectric Crystals• Sound Energy → Piezoelectric Crystals• Magnetic Energy → Electromagnets

Radiant Energy

• Applications: Flashlights, ceiling lamps

Thermal Energy

• Applications: Ovens, kettles

Mechanical (or Sound) Energy

• Applications: Quartz watches, speakers

Magnetic Energy

• Applications: Tape recorders, equipment for sorting scrap metal

Capacitors

• A capacitor is a device which stores electrical energy. • This device is composed of two metal electrical surfaces

separated by an insulating material – which blocks the flow of electrons.

• Capacitors stabilize fluctuating power supplies and provide strong charges in short periods of time.▫ Ex: A camera flash

Diodes

• A diode is a device which allows electric current to flow in one direction but not the other.

• Usually made of a semiconductor (silicon.)

• A diode acts much like a store turnstile. People can either enter or exit the store via the turnstile but they cannot do both.

Diodes

• There are many types of diodes.▫ Some diodes guide and block current. (Ex: TV remotes)▫ Some diodes convert alternating current into direct current.▫ Some diodes are electroluminescent meaning they give off light

when a current flows through them.

Transistors

• A transistor is an electronic device used to block or amplify an electric current.

• Made up of a small semiconductor (silicon)

• Can work in two different ways:▫ It can act as a switch, blocking the current.▫ It can alter the current, usually by amplifying it.

Transistors

• A transistor is made up of three parts:1. The collector2. The base3. The emitter

• Current flows from the collector to the emitter through the base, which acts like a door. It can either stop the current or facilitate its flow.

Transistors

• Applications: the field of electronics, any electronic equipment that processes data▫ Computers, cell phones, calculators, MP3

players, DVD players

Relays

• A relay is a component that opens or closes a circuit, using an electrical signal from another circuit.▫ The signal can come from a switch, a computer or a photoelectric

cell.

• The advantage of using a relay is that the control circuit and the circuit to be controlled remain separate; there is no electrical contact between the two.

Relays

• Applications: lighting system in a theatre, heating system in a public building, industrial motors and high-voltage appliances.