Transcript Unit 2 PPT- Date

Lecturer: Mr. Jerome Smith
Course: CAP
Basic Electric Circuits &
Components
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Introduction
SI Units and Common Prefixes
Electrical Circuits
Direct Currents and Alternating Currents
Resistors, Capacitors
Ohm’s, Power Law
Power Dissipation in Resistors
Resistors in Series and Parallel
Resistive Potential Dividers
Sinusoidal Quantities
Circuit Symbols
SI Units
Quantity
Capacitance
Charge
Current
Electromotive force
Frequency
Inductance (self)
Period
Potential difference
Power
Resistance
Temperature
Time
Quantity symbol
C
Q
I
E
f
L
T
V
P
R
T
t
Unit
Farad
Coulomb
Ampere
Volt
Hertz
Henry
Second
Volt
Watt
Ohm
Kelvin
Second
Unit symbol
F
C
A
V
Hz
H
s
V
W
Ω
K
s
Common Prefixes
Prefix
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 Circuits
 Electric charge
 an amount of electrical energy
 can be positive or negative
 Electric current
 a flow of electrical charge, often a flow of electrons
 conventional current is in the opposite direction to a
flow of electrons
 Current flow in a circuit
 a sustained current needs a complete circuit
 also requires a stimulus to cause the charge to flow
Section 7.2: Electric Current
 Static Electricity: build up of charges that pass
QUICKLY to another object
 Electric Current: continuous flow of charges through
a conductor
 Electromotive force and potential difference
 the stimulus that causes a current to flow is an e.m.f.
 this represents the energy introduced into the circuit by
a battery or generator
 this results in an electric potential at each point in the
circuit
 between any two points in the circuit there may exist a
potential difference
 both e.m.f. and potential difference are measured in
volts
 A simple circuit
 A water-based
analogy
Voltage
 Voltage 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
Current
 Currents in electrical circuits may be constant or may
vary with time
 When currents vary with time they may be
unidirectional or alternating
 When 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 Inductors
 Resistors provide resistance
 they oppose the flow of electricity
 measured in Ohms ()
 Capacitors provide capacitance
 they store energy in an electric field
 measured in Farads (F) Forumlae:
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Capacitors in Series: (1/CTOTAL) = (1/C1) + (1/C2) + (1/C3)
Capacitors in parallel: CTOTAL = C1 + C2 + C3 .....
 Inductors provide inductance
 they store energy in a magnetic field
 measured in Henry (H)
Check for Understanding
 What 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 light
 Ex: 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 Law
 The 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 Law
Power is the measure of how much work can be done in
a given amount of time.
 Did you know?
1. W = V x I
2. W = I2 x R ?
3. W = V2 / R ?
 Lets see!!
Sinusoidal
Quantities
 Length 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 Circuits
Series Circuits
Parallel Circuits
 _______ path(s) for current
 _______ path(s) for current
 Current ________________
 Current ________________
 Voltage ________________
 Break in circuit
_______________________
 Voltage ________________
 Break in circuit
_______________________
 Adding resistance in parallel
 Adding resistance in series
______________________
_______________________
Let’s Compare Series and Parallel Circuits
Series Circuits
Parallel Circuits
 1 path(s) for current
 multiple path(s) for current
 Current is the same at every
 Current can be different in each
branch
point
 Voltage drops at each resistor
 Voltage same across each resistance
 Break in circuit stops all current
 Break in circuit does not affect other
bulbs
 Adding resistance in series
 Adding resistance in parallel
decreases total current (dimmer
light bulbs)
increases total current
Group 1: inside/outside micrometers
Group 2: vernier callipers
Group 3: dial gauges
Group 4: depth gauges
Group 5: tone generator