Lecturer: Mr. Jerome Smith Course: CAP. Basic Electric Circuits & Components Introduction SI Units and Common Prefixes Electrical Circuits Direct Currents

Storey: Electrical & Electronic Systems © Pearson Education Limited 2004 OHT 2.1

Unit 2 | Using tools, equipment and other

devicesLecturer: Mr. Jerome Smith

Course: CAP


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


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


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


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


Section 7.2: Electric CurrentStatic Electricity: build up of charges that

pass QUICKLY to another objectElectric Current: continuous flow of

charges through a conductor


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


A simple circuit

A water-based analogy


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.


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)


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)


Check for UnderstandingWhat is voltage?

How is voltage generated? (3 ways)

What is current?


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)


What Affects Resistance?


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


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


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!!


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


Circuit Symbols



Key Points


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 _______________________


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


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

Documents

Lecturer: Mr. Jerome Smith Course: CAP. Basic Electric Circuits & Components Introduction SI Units and Common Prefixes Electrical Circuits Direct Currents