Electrical Functions Notes

Transcription

1 Electrical Functions Notes

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

3 Power Supplies Power supply is the electrical function performed by any component that can generate or provide and electric current in a circuit Battery Electrical Outlet Photovoltaic Cell

4 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

5 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

6 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

7 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

8 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.

9 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.

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

11 Closed Circuit A closed circuit is a circuit in which electric current flows in a loop. The light bulb is ON!

12 Open Circuit An open circuit is a circuit in which electric current cannot flow in a loop. The light bulb is OFF!

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14 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

15 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.

16 Number of contacts opened or closed at one time Number of possible paths 1 1 Single pole, double throw 1 2 Double pole, Single throw 2 1 Double pole, Double throw 2 2 Switch Single pole, Single throw Diagram

17 Single pole double throw

18 Double pole single throw

19 Double pole Double throw

20 Types of Switches Types can take many forms. Push-button Switch Rocker Switch Toggle Switch Magnetic Contact Switch

21 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.

22 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.

23 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.

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25 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.

26 Resistance Electrical resistance is expressed in ohms [Ω] Ex: Resistor A has an electrical resistance of 2500Ω.

27 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. (+ )

28 THE COLOR CODE FOR ELECTRICAL RESISTORS: DIGIT MULTIPLIE R TOLERANC ± ± 1% ± E 20% 2% COLOR BLACK BROWN RED Gold Silver ± 5% ± 10% ORANG E YELLOW GREEN BLUE VIOLET GREY WHITE GOLD SILVER

29 Resistor colour code example: Green blue yellow 56 x Ω + 5% or 56 x 104 Ω + 5% or 560 k Ω + 5% gold

30 What is the value of the resistor below? 41 x 105 ±10%

31 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)

32 Forms of Energy Type 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 Sun cellphone 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 microwave Fire

33 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

34 Radiant Energy Applications: Flashlights, ceiling lamps

35 Thermal Energy Applications: Ovens, kettles

36 Mechanical (or Sound) Energy Applications: Quartz watches, speakers

37 Magnetic Energy Applications: Tape recorders, equipment for sorting scrap metal

38 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

39 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.

40 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.

41 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.

42 Transistors A transistor is made up of three parts: The collector The base 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.

43 Transistors Applications: the field of electronics, any electronic equipment that processes data Computers, cell phones, calculators, MP3 players, DVD players

44 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.

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