2) basic of electricity

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Basic of Electrical System

Structure of an Atom

Atoms = Nucleus [protons(+ve) & neutron] + electrons(-ve)

The forces in the atom are repulsions between electrons andattraction between electrons and protons

Atom is electrically neutral Electrons that occupy the outermost filled orbit the valence

electronsresponsible for bonding The valence electron is slightly attracted to the nucleus so it tends

to fly out of orbit and attach to other atoms. Therefore it is calledfree electron

Various characteristics of materials are caused by the freeelectrons

Types of Electricity

Static Electr ic i tyProduced when a non-conductive material e.g. glass rod is rubbedwith a silk cloth, one surface becomes positively charged and theother negatively charged. Unless the two materials touched thecharges will remain in the glass rod and the silk cloth. It does notmove so it is called static electricity.

Nucleus (protons + neutrons)

Electron


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Dynam ic Electr ic i ty

Refers to a state in which there is a flow of free electrons. When thefree electrons are moving in constant direction direct current (DC).When the direction of motion and the size of current vary periodicallywith timealternating current (AC)

Electric Current (I) Electric current is the flow of electrons It is measured in amps (short for Amperes), A The amp is a measure of flow rate / how much electricity is

flowing per second

1 amp = 6.240 x 1024electrons per second

When current flows in a conductor or electrolyte, it can bring aboutthree actions:Heat generation

When current runs through a conductor, it produces heat e.g.headlights, fuses

Chemical actionWhen chemical activity occurs in an electrolyte, it causescurrent to flow e.g. battery

Magnetic actionWhen current flows in a wire or coil, it produces a magnetic fieldin the immediate environment e.g. ignition coil, alternator,starter motor

In automotive, magnetic and chemical action are used

Ammeter is used to measure current To measure the current flowing through a component in a circuit,

the ammeter must be connected in series with the rest of thecircuit


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For an electric current to flow, we need two things:A battery or a generator to make the electricity flowA complete circuit

Voltage (V) and Electromotive Force (EMF)When a lamp is connected to a battery by a wire, current will flow

from the battery to the lamp and the lamp will light up.

This is because there is abundant of free electrons at the batterynegative terminal and a shortage of free electrons at battery positiveterminal. This difference creates a pressure and this electricalpressure causes current to flow through the wire, lighting the lamp

Voltage is a measure of electrical pressure between two parts of a

circuit It is measured in volts, V 1 volt refers to the voltage that can cause 1 ampere of current to

flow in a conductor having a resistance of 1 ohm In automotive, the electrical pressure can be provided by a battery

or it can be produced by a generator Voltmeter is used to measure voltage


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To measure the voltage across a component in a circuit, thevoltmeter must connected in parallel with the rest of the circuit

.

Electrical Resistance(R)

In terms of resistance to the flow of current, materials may begrouped into three categories:

ConductorConductors are materials which permit electrons to flow freely fromatom to atom e.g. gold, copper, aluminum, silver

InsulatorInsulators are materials which impede the free flow of electrons fromatom to atom e.g. glass, rubber, plastics

SemiconductorA material that act as conductor or insulator depending on electricalcondition

Resistance is the opposition of a circuit to the flow of electriccurrent

It is measured in ohm () 1 ohm refers to the electrical resistance which is encountered

when 1 ampere of electric current flows at a voltage of 1 volt Factors that affect resistance value are material, temperature,

cross-sectional area, length and duration of usage

length, resistancecross-sectional, resistance


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A

lR

= resistivity (.m)l = length of a conductor (m)

A = cross-sectional area of conductor (m2)

Resistance increases as the temperature rises

Contact resistanceThe resistance causes by incomplete contact e.g. when a wire is notconnected firmly to the battery or load, or when a switch connectingtwo parts is corroded, electricity flows less easily and heat isgenerated. The heat promotes further corrosion and as a result,

contact resistance becomes even greater.

Contact resistance can be reduced by tightening the connection orcleaning the contacting area.


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Insulation resistanceA phenomenon in which electricity can flow between conductorsthrough an insulator under certain condition. Such conditions includebreakage of the insulator, which allows a leak current to flow through

the insulator, and flashover, involving dirt, water and other materialsadhering to the surface of the insulator.

Electrical Circuits When the electrons flow back to where they started from, it is

called a circuit In electrical circuits, current flows from the ___________ terminal

of the supply to the __________ terminal Any device that consumes electricity is called load. In electrical

circuit, all loads are regarded as resistance

Automotive Electrical CircuitsIn an automotive electrical circuit, one end of the wire from each loadreturning to the battery is connected to the vehicle body or frame;acting as a conductor, allowing current to flow through the body andback to the battery. The body or frame is then referred to as the bodyground (or earth) of the circuit


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Ohms Law

Current flow is directly proportional to the voltage and inverselyproportional to the resistance

I = V ; V=IRR

I = currentV = voltageR = resistance

Simple circuit A simple circuit consists of power supply (battery, alternator,

generator which supply electricity to the circuit), load (electricaldevice that uses electricity to produce work) and conductor(wires or car metal parts that carry current between power sourceand load)

Switch is an optional component to facilitate the control of thecircuit

Types of Circuit

Primary Circuits The first part of a two-part circuit The switch that control the circuit must be closed before any of

the other components in the circuit will work

Open circuitContinuity fault in the circuit e.g. broken wire, load or fuse; faulty

switchNo output from the load


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Close circuitPerfect, correct functioning circuit in which the switch is closedOutput is achieved from the loadIt is normal/working condition

Series Circuits In a series circuit, the components (switches, bulbs, fuses etc.)

are all connected so that the current flows first through one andthen through the next There are no branches; the current doesnt split into more than

one route Disadvantages If one component fail, the system will revert to open circuit Unable to control the operation of load separately Each load receive different voltage due to voltage drop

Parallel Circuits

In parallel circuit, the different components are connected ondifferent wires therefore the current can move through any ofseveral paths


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Electrical Circuits: Basic Theory

Series Connection


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Voltage Drop


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Parallel Connection


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Series-Parallel Connection


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What happen to the magnetic flux when we have a circular wirerather than a straight wire???

When a straight wire is bent, it becomes a circular coil andcreates a much larger, more powerful flux. When current flows in

a coil, the direction of the magnetic flux is such that N and S polesare created in the coil

When a conductor is wound in a tubular-shaped coil, it is calledsolenoid. S pole is created under the solenoid and N pole above it.

The number of magnetic lines of force increases as the number ofturns of the coil increases

When current flows in a solenoid, the number of magnetic lines offorce increases in proportion to the strength of the current

2) basic of electricity

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