Transcript Physics 108

Physics 110
Fundamentals of
Electronics
Fundamentals of Electronics
 Student
Information Sheet
 Syllabus
 Blackboard
 Books
Physics 110 Lab
 Labs
start on Monday, September 12
I have all labs posted in the calendar
What Can I Expect?
 Lecture
Style
PowerPoint, Chalkboard, Demos
Class participation is good.
 Exams
Exams problems are much like the homework
problems and in-class exercises.
Where do we find electrical circuits?

Communications
Radio, internet, telephone, television

Data Processing
Desktop computers, servers

Automobiles
displays, sensors, motors

Home
lighting, heating, appliances

Weather Stations
wind speed, precipitation, temperature

Power Plants
moving magnets, transformers
Chapter 2
DC Networks
Review Topics
 Scientific
Notation
 Units of Measure
Scientific Notation and Prefixes
1,000,000,000,000
 1,000,000,000
 1,000,000
 1,000
1
 0.001
 0.000001
 0.000000001
 0.000000000001

1012 – tera (T)
109 – giga (G)
106 – mega (M)
Write each
number in
103 – kilo
(k)
scientific notation and
give10
the0 metric prefix
for each.
-3
10 – milli (m)
10-6 – micro (m)
10-9 – nano (n)
10-12 – pico (p)
Electrical Units SI
Derived quantity
Name
Symbol
Expression
in terms of
other SI units
Expression
in terms of
SI base units
power, radiant flux
electric charge, quantity of electricity
watt
coulomb
W
C
J/s
-
m2·kg·s-3
s·A
electric potential difference
volt
V
W/A
m2·kg·s-3·A-1
capacitance
farad
F
C/V
m-2·kg-1·s4·A2
electric resistance
ohm
V/A
m2·kg·s-3·A-2
electric conductance
siemens
S
A/V
m-2·kg-1·s3·A2
magnetic flux
magnetic flux density
inductance
weber
tesla
henry
Wb
T
H
V·s
Wb/m2
Wb/A
m2·kg·s-2·A-1
kg·s-2·A-1
m2·kg·s-2·A-2
Celsius temperature
degree
Celsius
°C
-
K
Questions
1.
2.
3.
What is the difference between AC, DC, and
static electricity?
Why does a Van de Graaff Generator make
your hair stand up? (Give a technical answer.)
Why do clothes sometimes stick together
after you take them out of the dryer?
What is Electricity?
 From
the Greek word “elektron” that means
“amber”
 There are two types of electricity:
Static Electricity - no motion of free charges
Current Electricity - motion of free charges
 Direct
Current (DC)
 Alternating Current (AC)
2.2 Current

Current is the rate of flow of charge through a
conductor.
Conductor

materials with free electrons
 e.g. copper, aluminum, gold, most metals
Insulator

materials with no free electrons
 e.g. glass, plastics, ceramics, wood
Semiconductor

a class of materials whose electron conductivity is between that
of a conductor and insulator
 Examples: Silicon, Germanium
Can Air be a Conductor?
 Yep!
Electrical Current
 Current
- the rate of flow of charge through
a conductor
Conventional Current
 Direction of
flow of positive (+) charges
Electron Current
 Opposite
to that of conventional current
Equation for Current
I=Q/t
I = the current in Amperes (A)
Q = the amount of charge in Coulombs (C)
t = the time measured in seconds (s)
 The
charge of an electron is 1.6 x 10-19 C
Effect of Electric Currents on the Body
 0.001
A
 0.005 A
 0.010 A
 0.015 A
 0.070 A
can be felt
is painful
causes involuntary muscle contractions
causes loss of muscle control
can be fatal if the current last for more
than 1 second
Example Problem 2.0
 How
much charge will pass through a
conductor in 0.1 seconds if the current is
0.5 Amperes?
 How
many electrons are required for this
much charge?
Example 2.0
T
= 0.1 s I = 0.5 A
I = Q/t, so Q = I*t = (0.5 A)*(0.1 s) = 0.05 C
 Charge/e-
= 1.6 X 10-19 C/e# Charges = 0.05 C/ 1.6 X 10-19 C/e# Charges = 3.125 X 1017 e-
Example 2.1
 Determine
the current in amperes through a
wire if 18.726 x 1018 electrons pass through
the conductor in 0.02 minutes.
 18.726 x 1018 electrons, t = 0.02 min
Q = (18.726 x 1018 e-)(1.6 X 10-19 C/e-)
Q = 2.99616 C  3 C
 I = Q/t = 3 C/(0.02 min)(60 s/min)
 I = 2.4968  2.5 A
Example 2.2
 How
long will it take 120 C of charge to
pass through a conductor if the current is
2 A?
 I = Q/t, so t = Q/I = 120 C/2 A
t = 60 s
Example Problem 2.3 and 2.4
 Write
the following in the most convenient
form using Table 2.1:
(a) 10,000 V
(a) 104 V
-5 A
(b)
10
(b) 0.00001 A
-3 s
(c)
4
X
10
(c) 0.004 seconds
(d) 5.2 X 105 W
(d) 520,000 Watts
(e) 0.6 mA
(e) 0.0006 A
(f) 4.2 kV
(f) 4200 V
(g) 1.2 MV
(g)1,200,000 V
(h) 40 mA
(h)0.00004 A
Wire Gauge?
 AWG
= American Wire Gauge
 AWG numbers indicate the size of the
wire….but in reverse.
 For example, No. 12 gauge wire has a larger
diameter than a No. 14 gauge wire.
 What do we use to keep wires from
melting?
Answers: Fuses, Circuit Breakers, GFCI
Fuses
Circuit Breakers
GFCI = Ground Fault Current Interrupter
Used in kitchens and bathrooms
Trip quicker than circuit
breakers
2.3 Voltage
 Voltage
is the measure of the potential to
move electrons.
 Sources of Voltage
Batteries (DC)
Wall Outlets (AC)
 The
term ground refers to a zero voltage or
earth potential.
Digital Multimeters (DMM)
Measurement
Device
Circuit Symbol
Voltage
Voltmeter
V
Current
Ammeter
A
Resistance
Ohmmeter
Batteries
A battery is a type of voltage source that converts
chemical energy into electrical energy
 The way cells are connected, and the type of cells,
determines the voltage and capacity of a battery

More on Batteries
 Positive
(+) and Negative (-) terminals
 Batteries use a chemical reaction to create
voltage.
 Construction: Two different metals and Acid
e.g. Copper, Zinc, and Citrus Acid
e.g. Lead, Lead Oxide, Sulfuric Acid
e.g. Nickel, Cadmium, Acid Paste
 Batteries
“add” when you connect them in
series.
 Circuit Symbol:

Equation for Voltage
V=W/Q
V = the voltage in volts (V)
Q = the amount of charge in Coulombs (C)
W = the energy expended in Joules (J)
Example Problem 2.7
 Determine
the energy expended by a 12 V
battery in moving 20 x 1018 electrons
between its terminals.
Example Problem 2.8
 (a)
If 8 mJ of energy is expended moving
200 mC from one point in an electrical
circuit to another, what is the difference in
potential between the two points?
 (b)
How many electrons were involved in
the motion of charge in part (a)?
2.4 Resistance and Ohm’s Law
it the measure of a material’s
ability to resist the flow of of electrons.
 It is measure in Ohms (W).
 Ohm’s Law:
V=IR
V or E = voltage
I = current
R = resistance
 Resistance
Resistors
Example Problem 2.9
the voltage drop across a 2.2 kW
resistor if the current is 8 mA.
 Determine
Example Problem 2.10
 Determine
the current drawn by a toaster
having an internal resistance of 22 W if the
applied voltage is 120 V.
Example Problem 2.11
 Determine
the internal resistance of an
alarm clock that draws 20 mA at 120 V.
Equation for Resistance

R r
A
r = resistivity of the material from tables
 = length of the material in feet (ft)
A = area in circular mils (CM) = area of a
circle with a diameter of one mil (one
thousandth of an inch)
Example Problem 2.12
 Determine
the resistance of 100 yards of
copper wire having an 1/8 inch diameter.
r for copper is 10.37 circular mils/ft (I know, sigh)
L = 100 yds = 300 ft
ACM = (dmils)2 = (125mils)2 = 15,625
R = r ℓ/A = (10.37 CM/ft)(300 ft)/15625 CM
R = 0.199 W
Concept Questions
 How
can you determine the current through
a resistor if you know the voltage across it?
I = V/R
 How
can you change the resistance of a
resistor?
Change length, area, or temperature
Resistance depends on
Temperature
R 2  R11  a1 ( t 2  t1 )
R = resistances
t = temperatures
a = temperature coefficient from tables
Example Problem 2.15
resistance of a copper conductor is 0.3 W
at room temperature (20°C). Determine the
resistance of the conductor at the boiling
point of water (100°C).
 The
= R1[1 + a1(t2 – t1)]
 R2 = (0.3 W)[1 + 0.00393(100°-20°)]
 R2 = 0.394 W
 R2
Four-banded Resistor
Five-banded Resistor
Resistor Color Codes
0
1
2
3
4
5
6
7
8
9
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Calculator
Tolerance
5%
Gold
10%
Silver
Memorize this table.
Example Problem 2.17

Determine the manufacturer’s
guaranteed range of values for a
carbon resistor with color bands
of Blue, Gray, Black and Gold.
 68 X 100  5% = 68 W  3.4 W
Example Problem 2.18

Determine the color coding for a
100 kW resistor with a 10%
tolerance.
100 kW = 100,000 W
 Band 1 (Brown) Band 2 (Black)
 Band 3 (Yellow) Band 4 (Silver)
0
1
2
3
4
5
6
7
8
9
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Tolerance
5% Gold
10% Silver
Total Resistance for Resistors in Series
R T  R1  R 2
Total Resistance for Resistors in Parallel
1
1
1


R T R1 R 2
Potentiometers
 They
are three terminal devices with a
knob.
 The knob moves a slider which changes the
resistance between the terminals.
 Circuit Symbols:
What is the difference between E and V?
E
is the voltage supplied by a battery.
 V is the voltage measured across a resistor.
2.5 Power, Energy, Efficiency
 Power
is the measure of the rate of energy
conversion.
 Resistors convert electrical energy into heat
energy.
 Equation for Power:
P = I E Power Delivered by a Battery
P = I V Power Dissipated by a Resistor
 What are some other ways that we can write
this equation?
Power Equations
P
= IV but V = IR
 P = I(IR) = I2R
from Ohm’s Law I = V/R
 P = (V/R)V = V2/R
Example Problem 2.19
 Determine
the current drawn by a 180 W
television set when connected to a 120 V
outlet.
 P = 180 W
 V = 120 V
 I = P/V = 180 W/120 V = 1.5 A
Simple Circuit Problem
 Using
circuit symbols, draw a circuit for a
9V battery connected to a 10W resistor.
 Draw and label the direction of
conventional current.
 Now include a voltmeter in your sketch that
will measure the voltage drop across the
resistors. What will it read?
 Include a ammeter that will measure the
current through the resistor. What will it
read?
Simple Circuit Problem
 How
much power does the battery deliver?
 How much power does the resistor
dissipate?
Example Problem 2.20
 Determine
the resistance of a 1200W
toaster that draws 10A.
 Energy
and power are related:
W=Pt
W = energy in Joules
P = power in Watts
t = time in seconds
Example Problem 2.21
 Determine
the cost of using the following
appliances for the time indicated if the
average cost is 9 cents/kWh.
(a) 1200W iron for 2 hours
(b) 160W color TV for 3 hours and 30 minutes
(c) Six 60W bulbs for 7 hours.
 Efficiency
Po
   100%
Pi
Pi  Po  Pl
1hp  746 W
Example Problem 2.22
 Determine
the efficiency of operation and
power lost in a 5hp DC motor that draws
18A as 230V.
2.6 Series DC Networks
 Two
elements are in series if they have only
one terminal in common that is not connected
to a third current carrying component.
 Total Resistance
R T  R1  R 2  R 3  ...  R N
 Current
through a Series
E
I
RT
 Consider
Figure 2.32.
 E=24V,
 What
R1=2W, R2=4W, R3=6W
is RT?
 What is I?
 What is V1, V2 and V3?
 What is P1, P2, P3, and PT?
Kirchhoff’s Voltage Law
 “The
algebraic sum of the voltage rises and
drops around a closed path must be equal to
zero.”
 Vrises   Vdrops  0
 Voltage-divider
rule
“The voltage across any resistor in a series is some
fraction of the battery voltage.”
R xE
Vx 
RT
2.7 Parallel DC Networks
 Two
elements are in parallel if they have two
terminals in common.
 Total Resistance
1
1
1
1
1



 ... 
R T R1 R 2 R 3
RN
 Source
Current
E
I
RT
Concept Test
 For
resistors in series, what is the same for
every resistor? R, V or I?
 Answer:
I
 For
resistors in parallel, what is the same for
every resistor? R, V or I?
 Answer:
V
Kirchhoff’s Current Law
 “The
sum of the current entering a junction
must equal to the current leaving.”
 I entering   I leaving
Example Problem 2.28
 Using
Kirchhoff’s current law, determine
the currents I3 and I6 for the system of
Figure 2.42
I1 = I2 + I3
I3 + I 4 = I 5 + I 6
I3 = I1 - I2 = 6 A – 2 A = 4 A
I6 = I 3 + I 4 - I5 = 4 A + 6 A – 1 A = 9 A
 Consider
Figure 2.35.
 E1=100V
 E2=50V
 E3=20V
 R1=10W
 R2=30W
 R3=40W
 What
is I?
 What is V2?
Example Problem 2.25
 Find
V1 and V2 of Figure 2.36 using
Kirchhoff’s voltage law.
Voltage Sources in Series
 Current-divider
rule
“The current through any resistor in parallel with
other resistors is some fraction of the source
current.”
IR T
Ix 
Rx
Example Problem 2.26
 Determine
the following for the parallel
network in Fig. 2.40.
(a) RT
(b) I
(c) I2
(d) P3
2.8 Series-Parallel Networks
Solve for RT, I, I1, I2, and V1