Download - 2) Basic of Electricity
-
8/13/2019 2) Basic of Electricity
1/20
Page 1of 20
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
-
8/13/2019 2) Basic of Electricity
2/20
Page 2of 20
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
-
8/13/2019 2) Basic of Electricity
3/20
Page 3of 20
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
-
8/13/2019 2) Basic of Electricity
4/20
Page 4of 20
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
-
8/13/2019 2) Basic of Electricity
5/20
Page 5of 20
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.
-
8/13/2019 2) Basic of Electricity
6/20
Page 6of 20
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
-
8/13/2019 2) Basic of Electricity
7/20
Page 7of 20
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
-
8/13/2019 2) Basic of Electricity
8/20
Page 8of 20
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
-
8/13/2019 2) Basic of Electricity
9/20
Page 9of 20
Electrical Circuits: Basic Theory
Series Connection
-
8/13/2019 2) Basic of Electricity
10/20
Page 10of 20
-
8/13/2019 2) Basic of Electricity
11/20
Page 11of 20
Voltage Drop
-
8/13/2019 2) Basic of Electricity
12/20
Page 12of 20
-
8/13/2019 2) Basic of Electricity
13/20
Page 13of 20
Parallel Connection
-
8/13/2019 2) Basic of Electricity
14/20
Page 14of 20
-
8/13/2019 2) Basic of Electricity
15/20
Page 15of 20
-
8/13/2019 2) Basic of Electricity
16/20
Page 16of 20
Series-Parallel Connection
-
8/13/2019 2) Basic of Electricity
17/20
Page 17of 20
-
8/13/2019 2) Basic of Electricity
18/20
Page 18of 20
-
8/13/2019 2) Basic of Electricity
19/20
-
8/13/2019 2) Basic of Electricity
20/20
Page 20of 20
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