Basic Principles for Electronics Students

Electricity
Movement of electrons
Invisible force that provides
light, heat, sound, motion . . .

Electricity at the Atomic Level
Elements - The simplest form of matter
Atoms - Smallest piece of an element containing all of
the properties of that element

Components of an Atom
Nucleus
The center portion of
an atom containing the
protons and neutrons
Protons
Positively charged
atomic particles
Neutrons
Uncharged atomic
particles

Atomic Number
The atomic number is
equal to the number of
protons in the nucleus
of an atom.
The atomic number
identifies the element.
How many
protons are in
this nucleus?

Negatively charged
particles
Electron Orbitals
Orbits in which
electrons move around
the nucleus of an atom
Valence Electrons
The outermost ring of
electrons in an atom
3D
2D
Electrons

Electron Orbits
Orbit
Number
Maximum
Electrons
1 2
2
3
4
5
6
Valence
Orbit
2
72
32
8
Orbits closest to the nucleus fill first
18
50
8

Electron Orbits
Atoms like to have their valence ring either
filled (8) or empty(0) of electrons.
How many electrons are
in the valence orbit?
Copper
Cu
29
1
Is copper a conductor
or insulator? Conductor
Why?

How many electrons are in the valence orbit?
6
Is Sulfur a conductor or insulator?
Insulator
Why?
Sulfur
S
16
Electron Orbits

Electron Flow
An electron from one orbit can knock out an
electron from another orbit.
When an atom loses an
electron, it seeks another
to fill the vacancy.
Copper
Cu
29

Electron Flow
Electricity is created as electrons collide and
transfer from atom to atom.
Play Animation

Conductors and Insulators
Conductors Insulators
Electrons flow easily
between atoms
1-3 valence electrons in
outer orbit
Examples: Silver,
Copper, Gold, Aluminum
Electron flow is difficult
between atoms
5-8 valence electrons in
outer orbit
Examples: Mica, Glass,
Quartz

Conductors and Insulators
Identify conductors and insulators
Conductors Insulators

Electrical Circuit
A system of conductors and components
forming a complete path for current to travel
Properties of an electrical circuit include
Voltage Volts V
Current Amps A
Resistance Ohms Ω

Current
The flow of electric charge
When the faucet (switch) is off,
is there any flow (current)?
NO
When the faucet (switch) is on,
is there any flow (current)?
YES
Tank (Battery) Faucet (Switch)
Pipe (Wiring)
- measured in AMPERES (A)

Current in a Circuit
When the switch is off, there is no current.
When the switch is on, there is current.
off on
off on

Current Flow
Conventional Current assumes
that current flows out of the positive
side of the battery, through the
circuit, and back to the negative
side of the battery. This was the
convention established when
electricity was first discovered, but
it is incorrect!
Electron Flow is what actually
happens. The electrons flow out of
the negative side of the battery,
through the circuit, and back to the
positive side of the battery.
Electron
Flow
Conventional
Current

Engineering vs. Science
The direction that the current flows does not affect what the
current is doing; thus, it doesn’t make any difference which
convention is used as long as you are consistent.
Both Conventional Current and Electron Flow are used. In
general, the science disciplines use Electron Flow, whereas
the engineering disciplines use Conventional Current.
Since this is an engineering course, we will use Conventional
Current .
Electron
Flow
Conventional
Current

Voltage
The force (pressure) that causes
current to flow
When the faucet (switch) is off, is there any pressure (voltage)?
YES – Pressure (voltage) is pushing against the pipe, tank, and
the faucet.
When the faucet (switch) is on, is there any pressure (voltage)?
YES – Pressure (voltage) pushes flow (current) through the
system.
Pipe (Wiring)
- measured in VOLTS (V)

Voltage in a Circuit
The battery provides voltage that will push
current through the bulb when the switch is on.
off on
off on

Resistance
The opposition of current flow
What happens to the flow (current) if a rock
gets lodged in the pipe?
Flow (current) decreases.
Pipe (Wiring)
- measured in Ohms (Ω)

Resistance in a Circuit
Resistors are components that create resistance.
Reducing current causes the bulb to become
more dim.
off on
Resistor

Multimeter
An instrument used to measure the
properties of an electrical circuit,
including
Voltage Volts
Current Amps
Resistance Ohms

Measuring Voltage
Set multimeter to the proper V range.
Measure across a component.
Light
Resistor
Battery
Switch

Measuring Current
Set multimeter to the proper ADC range.
Circuit flow must go through the meter.
Light
Resistor
Battery
Switch

Measuring Resistance
Set multimeter to the proper Ohms range.
Measure across the component being tested.
Power must be off or removed from the circuit.
Light
Resistor
Battery
Switch

Ohm’s Law
Quantities Abbreviations Units Symbols
Voltage V Volts V
Current I Amperes A
Resistance R Ohms Ω
If you know 2 of the 3 quantities, you can solve for the third.
V=IR I=V/R R=V/I
The mathematical relationship between current, voltage,
and resistance
Current in a resistor varies in direct proportion to the
voltage applied to it and is inversely proportional to the
resistor’s value

Ohm’s Law Chart
V
I R
x
Cover the quantity that is unknown.
Solve for V
V=IR

V
I R
I=V/R
Ohm’s Law Chart
Solve for I

V
I R
R=V/I
Ohm’s Law Chart
Solve for R

Example: Ohm’s Law
The flashlight shown uses a 6 volt battery
and has a bulb with a resistance of 150 .
When the flashlight is on, how much
current will be drawn from the battery?
VT =
+
-
VR
IR
Schematic Diagram
mA
40
A
0.04
150
V
6
R
V
I R
R





V
I R

Circuit Configuration
Series Circuits
• Components are
connected end-to-end.
• There is only a single
path for current to flow.
Parallel Circuits
• Both ends of the components
are connected together.
• There are multiple paths for
current to flow.
Components
(i.e., resistors, batteries, capacitors, etc.)
Components in a circuit can be connected in one
of two ways.

Kirchhoff’s Laws
Kirchhoff’s Voltage Law (KVL):
The sum of all of the voltage drops in a
series circuit equals the total applied voltage
Kirchhoff’s Current Law (KCL):
The total current in a parallel circuit equals
the sum of the individual branch currents

Series Circuits
A circuit that contains only one path for current flow
If the path is open anywhere in the circuit, current
stops flowing to all components.

Characteristics of a series circuit
• The current flowing through every series component is equal.
• The total resistance (RT) is equal to the sum of all of the
resistances (i.e., R1 + R2 + R3).
• The sum of all of the voltage drops (VR1 + VR2 + VR3) is equal to
the total applied voltage (VT). This is called Kirchhoff’s Voltage
Law.
VT
+
-
VR2
+
-
VR1
+ -
VR3
+
-
RT
IT
Series Circuits

Example: Series Circuit
For the series circuit shown, use the laws of circuit theory to
calculate the following:
• The total resistance (RT)
• The current flowing through each component (IT, IR1, IR2, &
IR3)
• The voltage across each component (VT, VR1, VR2, & VR3)
• Use the results to verify Kirchhoff’s Voltage Law.
VT
+
-
VR2
+
-
VR1
+ -
VR3
+
-
RT
IT
IR1
IR3
IR2

Solution:
V
I R
T
R R1 R2 R3
  
Total Resistance:
T
T
T
V
I (Ohm's Law)
R

Current Through Each Component:
T
R 220 470 1.2 k
     
   
T
R 1900 1.9 k
 

T
12 v
I 6.3 mAmp
1.89 k
   
T R1 R2 R3
Since this is a series circuit:
I I I I 6.3 mAmp

R1 R1
V I R1 (Ohm's Law)
  
Voltage Across Each Component:
V
I R
Solution:
  
R1
V 6.349 mA 220 Ω 1.397 volts
R2 R2
V I R2 (Ohm's Law)
 
  
R2
V 6.349 mA 470 Ω 2.984 volts
R3 R3
V I R3 (Ohm's Law)
 
  
R3
V 6.349 mA 1.2 K Ω 7.619 volts

T R1 R2 R3
V V V V
  
Verify Kirchhoff’s Voltage Law:
Solution:
1.397 2.984 7.619
  
12 v v v v
12 v 12 v


Parallel Circuits
A circuit that contains more than one path for current
flow
If a component is removed, then it is possible
for the current to take another path to reach
other components.

Characteristics of a Parallel Circuit
• The voltage across every parallel component is equal.
• The total resistance (RT) is equal to the reciprocal of the sum of the
reciprocal:
• The sum of all of the currents in each branch (IR1 + IR2 + IR3) is equal to
the total current (IT). This is called Kirchhoff’s Current Law.
3
2
1
T
3
2
1
T
R
1
R
1
R
1
1
R
R
1
R
1
R
1
R
1






+
-
+
-
VR1
+
-
VR2 VR3
RT
VT
IT
+
-
Parallel Circuits

For the parallel circuit shown, use the laws of circuit theory to
calculate the following:
• The total resistance (RT)
• The voltage across each component (VT, VR1, VR2, & VR3)
• The current flowing through each component (IT, IR1, IR2, & IR3)
• Use the results to verify Kirchhoff’s Current Law.
42
+
-
+
-
VR1
+
-
VR2 VR3
RT
VT
IT
+
-
IR1 IR2 IR3
Example Parallel Circuits

Total Resistance:
volts
15
V
V
V
V
:
circuit
parallel
a
is
this
Since
R3
R2
R1
T 



1
1 1 1
T
1 2 3
R
R R R

 
Voltage Across Each Component:
Solution:
1
1 1 1
T
R
470 2.2 k 3.3 k

 
  
346.59
  
T
R = 350

R1
R1
V
I (Ohm's Law)
R1

V
I R
Current Through Each Component:
Solution:
  

R1
R1
V 15 v
I 31.915 mA=32 mA
R1 470
  

R2
R2
V 15 v
I 6.818 mA = 6.8 mA
R2 2.2 k
.545
  

R3
R3
V 15 v
I 4 mA= 4.5mA
R3 3.3 k
  

T
T
T
V 15 v
I 43.278 mA = 43 mA
R 346.59

Verify Kirchhoff’s Current Law:
T R1 R2 R3
I I I
I
  
Solution:
43.278 mA=31.915 mA+6.818 mA+4.545 mA

43.278 mA (43 mA) 43.278 mA (43mA)

Combination Circuits
Contain both series and parallel arrangements
What would happen if you removed light 1? light
2? light 3?
1
2 3

Electrical Power
 
P I V
Electrical power is directly related to
the amount of current and voltage
within a system.
Power is measured in watts

Image Resources
Microsoft, Inc. (2008). Clip Art. Retrieved November 20, 2008, from
http://office.microsoft.com/en-us/clipart/default.aspx

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