Transcript ELECTRONICS - The Basics Atomic Structure

Motor Vehicle Section
Automotive Electrics Course
Level 1
Morning Contents
Day One Contents
1. Atomic Structure
Conductors (Copper)
Insulators (Plastics/Rubber)
2. Units of Electrical Measure
Current (Amps)
Voltage (Potential Difference & EMF)
Resistance (Ohm’s)
Power (Watts)
3. Basic Symbols and Circuits
Circuit Symbols
Series circuits and calculations
Parallel circuits and calculations
ELECTRONICS The Basics
Atomic Structure
All matter is composed of substances called
‘ELEMENTS’. Elements are the purest and
simplest substances and make up the ‘PERIODIC
TABLE’, something that you may have heard
mentioned in Chemistry lessons at school.
For example the Chemical make up of ‘WATER’ is given as H2O.
Two parts (Atoms) of Hydrogen combined with one part (Atom) of
Oxygen. A Molecule of Water.
ELECTRONICS The Basics
PERIODIC TABLE
ELECTRONICS The Basics
Atomic Structure
electrons
protons
nucleus
neutrons
Positive ION
Negative ION
ELECTRONICS - The Basics
Atomic Structure
Neutrons do not carry an electrical charge, combine
with protons, which are positively charged to make
up the nuclei of all atoms, neutrons and protons do
attract each other strongly when they are close
together in the nucleus of an atom. However,
electrons, which are negatively charged, are held
much more weakly to atoms, and it is this weakness
upon which electronics is based.
ELECTRONICS - The Basics
Atomic Structure
It is thought that Electrons orbit the nucleus of atoms
in shells (like the planets orbiting the sun). In these
shells there should be a specific number of electrons.
The number of electrons in the shells will be
dependant on the element/material in question, but
the inner shells are always filled before the outer
shells.
If an atom has a complete outer shell, then it is
thought that the electrons are tightly bonded and the
material will not conduct electricity very well
(INSULATOR)
Nucleus
29+
Loosely held
Electron
Electrons
Copper Atom
The above gives details of Coppers atomic structure, with a
single electron in the outer shell, which can be passed from
atom to atom. A GOOD CONDUCTOR.
Please complete Exercise 1 in the assessment book
The above gives details of Coppers atomic structure, with a
single electron in the outer shell, which can be passed from
atom to atom. A GOOD CONDUCTOR.
Please complete Exercise 1 in the assessment book
When a link is placed across a battery then the surplus
electrons in the NEGATIVE end of the battery try to fill the
‘holes’ at the POSITIVE end of the battery
The Rate of Flow of Electrons from the negative side of the battery to
the positive side of the battery is called
CURRENT FLOW
A battery when fully charged is filled with
positive ions at one end and negative ions at
the other
The difference in pressure causes electrons to flow, this
potential difference is called
VOLTAGE
0 psi
50
psi
100 psi
50 psi
If a restriction is now put into the link this has the effect of
reducing the electron(current) flow This is call a
RESISTOR
and is measured in
OHMS
To help understanding of the basic principles it often helps to
use a WATER ANALAGY
Water pressure
Voltage (volts)
Water Flow
Current (amps)
Tap
Resistor (Ohms)
Turbine
Power (watts)
OHMS LAW (Ω)
G S Ohms in 1827 Stated that;
The current flowing through a metallic
conductor at a constant temperature is
proportional to the potential difference
applied to its ends
Lets now analyse this Statement
The current flowing
through a metallic
conductor
The amount of current flow in a circuit,
measured in amps
Metallic conductor could be a length of copper wire
is proportional
When one goes up the other goes up,
and when one goes down the other goes
down
potential difference applied to its
ends
The difference in electrical potential at
either end - Voltage
Measured in volt
The current flowing through a metallic conductor
at a constant temperature is proportional to the
potential difference applied to its ends
If there is an increase in voltage then there will be a
corresponding increase in current flowing
If there is an increase in resistance then there will be a
corresponding decrease in current flowing
therefore
VOLTS = AMPS X RESISTANCE
OR
AMPS = VOLTS
RESISTANCE
OR
RESISTANCE = VOLTS
AMPS
V = Voltage (Volts)
I = Current (Amps)
R = Resistance (Ohm’s)
V
I
R
Ohm’s Law Example
In a 24volt truck circuit, what would be the
current flow through a 3Ω resistor?
8 A ‘s
Please complete Exercise 2 in the Assessment book
CIRCUITS
A circuit consists of
A Supply such as a Battery,
A Component such as a Bulb,
A method of control such as a switch
And
Sufficient wiring to allow current to flow from one side
of the battery to the other
A CIRCUIT PROTECTION DEVICE A FUSE
Circuit Symbols
To ensure repair personnel can attend to
failures in electrical circuits. Components are
given designated symbols for universal
standardisation. The most common standards
these days are IEC (International
Electrotechnical Commission) or DIN
(Deutsches Institut für Normung ). Which are
replacing the old British Standard. Examples
of some of these symbols will be discussed
on the next few slides.
TYPES OF CIRCUIT
SERIES CIRCUIT
THE CURRENT HAS TO FLOW
THROUGH EACH RESISTOR IN TURN
TYPES OF CIRCUIT
PARALLEL CIRCUIT
5Ω’s
4Ω’s
3Ω’s
THE CURRENT SPLITS AND DIVIDES
BETWEEN EACH BRANCH IN THE
CIRCUIT
TYPES OF CIRCUIT
OPEN CIRCUIT
AN OPENING IN THE CIRCUIT
NO CURRENT CAN FLOW
TYPES OF CIRCUIT
CLOSED CIRCUIT
NO OPENING IN THE CIRCUIT
CURRENT WILL FLOW
TYPES OF CIRCUIT
SHORT CIRCUIT
COMPONENT IS BYPASSED
EXCESSIVE CURRENT WILL FLOW
TYPES OF CIRCUIT
SERIES CIRCUIT
Resistors are placed in a series (one after the other)
Current remains constant throughout the circuit
Voltage drops across each resistor
SERIES CIRCUIT RESISTOR VALUES
To find the total resistance, just add up the value of each
resistor
R1 3Ω
R3
R2
5Ω
4Ω
RT = R1+R2+R3
RT = 3+4+5
RT = 12 Ω
Please complete exercise 3 in
the assessment book.
PARALLEL CIRCUITS RESISTOR VALUES
In a parallel
circuit the
voltage will
be constant
and the
current flow
in each
branch adds
up to the total
current flow.
PARALLEL CIRCUITS RESISTOR VALUES
There are two ways to calculate the resistance of a parallel
circuit.
The easiest way is to work with only two resistance values
at one time and apply the formula below.
RT = R1 X R2
R1 + R2
PARALLEL CIRCUITS RESISTOR VALUES
Calculate the total
resistance of this
circuit.
PARALLEL CIRCUITS RESISTOR VALUES
R R
3  4 12
R 


 1.71' s
R R
3 4
7
1
2
1
2
T
PARALLEL CIRCUITS RESISTOR VALUES
If there are more than two resistors,
the resistance value of two at a time
can be calculated and then put back
into the formula.
Please follow the explanation from your
tutor, for the following circuit.
PARALLEL CIRCUITS RESISTOR VALUES
5Ω’s
4Ω’s
3Ω’s
Please complete exercise 4 in the assessment booklet.
ELECTRICAL POWER
Power is the rate of doing work. This applies
to electrical components as the energy stored
in a battery can be converted to mechanical
work in a motor (Power Dissipated).
How do we know how much work an electrical
component is doing?
ELECTRICAL POWER
Power can be calculated by using a formula,
which is easy to use when a magic triangle is
adopted as in Ohm’s Law.
Electrical power is said to be the product of
voltage and current.
P=VxI
P = Power (Watts)
V = Voltage (Volts)
I = Current (Amps)
P
V
I
How much power is dissipated in a circuit with a
motor that is drawing 7 amps? Assume that the
circuit is connected to a 24 volt supply.
P=IxV
P = 7 x 24
P = 168 watts
Please complete exercise 5 in the assessment booklet.