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Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.1
Unit 2 | Using tools, equipment and other
devicesLecturer: Mr. Jerome Smith
Course: CAP
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.2
Basic Electric Circuits & Components
IntroductionSI Units and Common PrefixesElectrical CircuitsDirect Currents and Alternating CurrentsResistors, CapacitorsOhm’s, Power LawPower Dissipation in ResistorsResistors in Series and ParallelResistive Potential DividersSinusoidal QuantitiesCircuit Symbols
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.3
SI UnitsQuantity Quantity symbol Unit Unit symbol
Capacitance C Farad FCharge Q Coulomb CCurrent I Ampere AElectromotive force
E Volt V
Frequency f Hertz HzInductance (self) L Henry HPeriod T Second sPotential difference
V Volt V
Power P Watt WResistance R Ohm ΩTemperature T Kelvin KTime t Second s
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.4
Common PrefixesPrefix Name Meaning (multiply by)
T tera 1012
G giga 109
M mega 106
k kilo 103
m milli 10-3
micro 10-6
n nano 10-9
p pico 10-12
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.5
Electrical CircuitsElectric charge
an amount of electrical energycan be positive or negative
Electric currenta flow of electrical charge, often a flow of electronsconventional current is in the opposite direction to
a flow of electronsCurrent flow in a circuit
a sustained current needs a complete circuitalso requires a stimulus to cause the charge to flow
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.6
Section 7.2: Electric CurrentStatic Electricity: build up of charges that
pass QUICKLY to another objectElectric Current: continuous flow of
charges through a conductor
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.7
Electromotive force and potential differencethe stimulus that causes a current to flow is an
e.m.f.this represents the energy introduced into the
circuit by a battery or generatorthis results in an electric potential at each
point in the circuitbetween any two points in the circuit there
may exist a potential differenceboth e.m.f. and potential difference are
measured in volts
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.8
A simple circuit
A water-based analogy
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.9
VoltageVoltage is created by
a chemical cell (battery) when it changes chemical energy to electrical energy
by a generator when it changes mechanical energy to electrical energy
by a solar cell when it changes light energy to electrical energy.
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.10
Direct Current and Alternating CurrentCurrents in electrical circuits may be
constant or may vary with timeWhen currents vary with time they may be
unidirectional or alternatingWhen the current flowing in a conductor
always flows in the same direction this is direct current (DC)
When the direction of the current periodically changes this is alternating current (AC)
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.11
Resistors, Capacitors and InductorsResistors provide resistance
they oppose the flow of electricitymeasured in Ohms ()
Capacitors provide capacitancethey store energy in an electric field
measured in Farads (F) Forumlae: Capacitors in Series: (1/CTOTAL) = (1/C1) + (1/C2) + (1/C3)
Capacitors in parallel: CTOTAL = C1 + C2 + C3 .....
Inductors provide inductancethey store energy in a magnetic fieldmeasured in Henry (H)
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.12
Check for UnderstandingWhat is voltage?
How is voltage generated? (3 ways)
What is current?
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.13
Resistance Resistance: the tendency for a material
to oppose the flow of electrons Changes electrical energy into thermal
energy and lightEx: lightbulb filament
Resistance is measured in Ohms (Ω)
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.14
What Affects Resistance?
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.15
Household Circuits:
Fuse: a small piece of metal that melts if the current becomes too high
Circuit Breaker: contains a small piece of metal that bends when it gets hot bending causes a switch to flip and opens the circuit
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.16
Ohm’s LawThe current flowing in a conductor is directly
proportional to the applied voltage V and inversely proportional to its resistance R
V = IR
I = V/R
R = V/I
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.17
Power LawPower is the measure of how much work can be
done ina given amount of time.Did you know?
1. W = V x I2. W = I2 x R ?3. W = V2 / R ?
Lets see!!
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.18
Sinusoidal QuantitiesLength of time between corresponding points in successive cycles is the period T
Number of cycles per second is the frequency f
f = 1/T
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.19
Circuit Symbols
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.20
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.21
Key Points
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.22
Let’s Compare Series and Parallel CircuitsSeries Circuits Parallel Circuits
_______ path(s) for current
Current ________________
Voltage ________________
Break in circuit _______________________
Adding resistance in series ______________________
_______ path(s) for current
Current ________________
Voltage ________________
Break in circuit _______________________
Adding resistance in parallel _______________________
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.23
Let’s Compare Series and Parallel CircuitsSeries Circuits Parallel Circuits
1 path(s) for current
Current is the same at every point
Voltage drops at each resistor
Break in circuit stops all current
Adding resistance in series decreases total current (dimmer light bulbs)
multiple path(s) for current
Current can be different in each branch
Voltage same across each resistance
Break in circuit does not affect other bulbs
Adding resistance in parallel increases total current
Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.24
Assignment Explain using a detailed diagram how the equipment is used. Use MS PPT to present your findings. Due 05/12/14 WILL BE GRADED. Include video and text in PPT
Group 1: inside/outside micrometersGroup 2: vernier callipersGroup 3: dial gaugesGroup 4: depth gauges Group 5: tone generator