Download Chapter 3 - Hingham Schools

Voltage
Chapter 3
Voltage (V or E)
Supplies the force or pressure
required to move electrons
through a circuit.
AKA – Electromotive Force EMF
Unit – Volt (V)
Voltage Sources
Friction – Van de Graaf Generator
Voltage Source
Generator – Most Common
Voltage Source
Cell – Battery: Chemical Reaction
Voltage Source
Photovoltaic Cell
Light → Voltage
Voltage Source
Thermocouple
Heat → Voltage
Voltage Source
Piezoelectric Effect
Pressure → Voltage
Cells and Batteries
Primary Cells
Cannot be Recharged
Cells and Batteries
Secondary Cells
Can be Recharged
Connecting Voltage Sources
Series Aiding
Series Opposing
+
-
+
+
+
--
Voltage Sources
Voltage sources added in Series
increase the Voltage and the Current
stays the same.
V = 1.5v
I = 1A
V = 4.5v
I = 1A
V = 4.5v
I = 1A
Voltage Sources
Voltage sources added in Parallel
increase the Current and the Voltage
stays the same.
V = 1.5v
I = 1A
V = 1.5v
I = 3A
V=1.5v
I =3A
Battery: V = 1.5v, I = 1A
V=3v I=1A I=1A I=1A
Example
V=3v
I= 3A
V=3v
I=3A
VT = 9v and IT = 500ma
Battery: V = 1.5v and I = 100mA
100mA
9v
100mA
100mA
100mA
100mA
VT = 9v
IT =500mA
VT = 9v
IT =500mA
Voltage Rise
Voltage Rise can be defined as
the energy added to a circuit.
Voltage Drop
A Voltage Drop is defined as
the energy removed or used in
a circuit.
Voltage Drop
Earth Ground
Zero Voltage reference point.
Limits build up of electrical charge.
Limits exposure to high voltages.
Electrical Ground
Ground is defined as the zero
reference point which against
all voltages are measured.
Electrical Ground in a Car
Jumping a Car
Bad
Battery
Ohm’s Law
The Current(I) in a circuit is directly
proportional to the Voltage(E,V) and
inversely proportional to the
Resistance(R).
V
I=
R
Ohm’s Law
V
I R
Find: V
V=
x
IR
Ohm’s Law
V
I R
Find: R
R = V/I
Ohm’s Law
V
I R
Find: I
I = V/R
Ohm’s Law Units
Vv
IA RΩ
Ohm’s Law Units
V(v)
ImA RkΩ
Ohm’s Law Example
Vv
IA RΩ
R=2Ω, V=12v
Find: I
I = V/R
=12v/2Ω
I = 6A
Ohm’s Law Example
Vv
V=120, I=60mA
Find: R
R = V/I
ImA RkΩ
=120v/60mA
R = 2kΩ
Ohm’s Law Example
Vv
R=10kΩ, I=12mA
Find: V
V = IxR
ImA RkΩ
=12mAx10kΩ
V = 120v
Wheel of Answers
Vv
IA RΩ
Vv
ImA RkΩ
Power
Power is how fast work is done.
Work is done when force causes motion.
Electric Force: Voltage
Moving: Electrons
Power
Power: P
Unit for Power: Watt
Watt: W
P = IV
Power Law
P
IV
Find: P
P=
x
IV
Power Law
P
IV
Find: V
V = P/I
Power Law
P
IV
Find: I
I = P/V
Power Law Units
PW
IA VV
Power Law Units
PmW
ImA VV
How much power does a 12V computer
fan use if it is drawing 1.5A?
V = 12V
I = 1.5A
P=IV
P=(1.5A)(12V)
P = (18W)
Combining Ohm’s and Power Laws
P=
P=
2
IR
2
V
R
V
IR
Classwork

Read the following Chapters:
»Chapter 2: All
»Chapter 3: All
»Chapter 4: Pages 32-44
»Chapter 5: Pages 49-52

Answer the questions after each section:
Write down question and answer!!!
•
Perform Self-Test at the end of the chapter