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Sec. 20.1, Electric Charge & Static Electricity
 Electric
Charge
 Electric
charge is a property that causes sub
atomic particles like protons and electrons to
attract or repel each other.
 There are two types of electric charge.
A positive charge, like protons have.
 This
A
produces a positively charged cation.
negative charge, like electrons have.
 This
produces a negatively charged anion.
Sec. 20.1, Electric Charge & Static Electricity
 Electric
 An
charge (Continued)
excess or shortage of electrons produces a
positive or negative net electric charge.
An atom in its ground state has an overall
net charge of 0.
If it gains excess electrons, its net charge
becomes negative
If it loses electrons, its net charge becomes
positive.
The Coulomb (C) is the SI unit for electric
charge
Sec. 20.1, Electric Charge & Static Electricity
 Electric
 Like
Forces
charges repel
Two particles that are both positively
charged, or both negatively charged will
repel (push away) from each other.
 Opposite charges attract
Two particles with opposite charges (one
positive and one negative will attract each
other.
Sec. 20.1, Electric Charge & Static Electricity
 Electric
 Electric
Forces (continued)
force is the force of attraction or
repulsion between charged objects.
 Charles-Augustin de Coulomb (1736-1806) is
credited with pioneering research in electric
forces.
 Electric forces obey a law similar to that of
the law of universal gravitation.
Sec. 20.1, Electric Charge & Static Electricity
 Electric
Forces (continued)
 The
electric force on two objects is directly
proportional to the net charge on each object.
 In
other words, the greater the net charge, the
stronger the attraction.
 The
electric force on two objects is inversely
proportional to the distance between the
objects.
 In
other words, the greater the distance between
two charged objects. The weaker the electric
force.
Sec. 20.1, Electric Charge & Static Electricity
 Electric
 As
Forces (continued)
the distance between two charged particles
is doubled. The electric force between them
becomes one fourth as strong.
Sec. 20.1, Electric Charge & Static Electricity
 Electric
 An
Fields
electric field is the effect that an electric
charge has on other charges around it in
space.
 The strength of an electric field depends on
the amount of charge that produces the field
and the distance from the charge.
 An electric field exerts an electric force on any
object placed in the field.
 What determines the strength of the field?
Notice the fields created by the two charges. Whether
the charge is positive or negative, the field is always
strongest near the charge.
Sec. 20.1, Electric Charge & Static Electricity
 Static
Electricity and Charging
 Static electricity is the study of the behavior
of charges and how they are transferred
between objects.
 There are three ways a charge can be
transferred.
 Charging
by friction
 Charging by contact
 Charging by induction
Three Ways To Transfer Charges
Contact
Friction
Induction
Sec. 20.1, Electric Charge & Static Electricity
 Static
Electricity and Charging
 Charging
by Friction
Rubbing two objects together can cause
charge to move from one object to the
other.
Rubbing a balloon on your hair causes
electrons to move from your hair to the
balloon because the rubber has a greater
ability to attracts electrons.
Walking across the carpet does the same
thing.
Sec. 20.1, Electric Charge & Static Electricity
 Charging
 When
by Contact
a body physically touches a charged
object, it can acquire a charge from the
charged object.
 When the charge is acquired, the charge from
the original charged body is reduced.
Sec. 20.1, Electric Charge & Static Electricity
 Charging
by Induction
 Induction
charging involves the charging of
an object without the objects actually
touching.
 An example of this is when you reach for a
metal door knob, the electrons in your finger
cause the free electrons in the metal door
knob to migrate away from your negatively
charged hand.
Notice how the electrons in the negatively charged finger cause
the negative charge to move to the back of the door knob.
Sec. 20.1, Electric Charge & Static Electricity
 Static
Discharge
 Static
discharge occurs when a pathway
through which charges can move forms
suddenly.
Lightning is one of the most familiar
examples of static discharge.
A more common example is the shock you
sometimes get after walking over carpet and
reaching for a metal object like a door
knob.
Mt. Arenal near Liberia, Costa Rica Notice
the lightning strikes produced by the
ionized particles created in the
Section 20.1 Quiz

1. Protons Carry a ________ charge and
electrons carry a ________charge.

2. When you increase the distance between two
charged particles, the electric force between
them is _________.

3. The effect an electric charge has on other
objects around it in space is called a/an
_______ ________.
Section 20.1 Quiz

4. The two things that determine electric field
strength are?

5. The three ways to transfer static electric
charges are ___________, ____________,
and ___________.
Sec. 20.2, Electric Current & Ohm’s Law
 Electric
Current
 Electric
current is a continuous flow of
electric charge.
 Direct current and alternating current are the
two types of current.
 The SI unit for current is the ampere or
amp, symbolized by the letter A.
Sec. 20.2, Electric Current & Ohm’s Law
 Electric
 Direct
Current (continued)
Current
This current only flows in one direction.
It is symbolized by the letters DC.
This current is mostly produced by some
sort of battery, such as a flashlight or car
battery.
Sec. 20.2, Electric Current & Ohm’s Law
 Electric
Current (continued)
 Alternating
Current
Alternating current is a flow of current
that regularly reverses direction.
Most household wiring and wiring in
commercial buildings is to accommodate
alternating current.
Sec. 20.2, Electric Current & Ohm’s Law
 Conductors
 Electrical
and Insulators.
Conductors mostly metals like
copper, aluminum, silver, etc. are used as a
pathway in which current can move.
 Electrical insulators (usually non-metal) is a
coating around a wire that does not conduct
electricity. This keeps the current on the
pathway where it is needed and prevents short
circuits.
Sec. 20.2, Electric Current & Ohm’s Law
 Resistance
 Resistance
is the opposition to flow of
charges in a material.
 The SI unit for resistance is the ohm (Ω).
 Three things affect the resistance of a
material.
 The
material’s thickness
 The material’s length
 The temperature of the material
Sec. 20.2, Electric Current & Ohm’s Law
 Resistance
 As
(continued)
electrons move through a wire, thermal
energy (heat) is produced as electrons collide
with other electrons and ions in the wire.
 As heat builds up in a conductor, its resistance
increases and its conductivity decreases.
Sec. 20.2, Electric Current & Ohm’s Law
 Resistance
 Because
(continued)
of problems with resistance it is
important to choose the correct conductor
material and size for each application.
 Superconductors
Usually used in specialized applications
It is a material that has almost no resistance
when cooled down to low temperatures.
Sec. 20.2, Electric Current & Ohm’s Law
 Voltage
 In
order for charge to flow in a conducting
wire, the wire must be connected to a
complete loop that includes a source of
electrical energy.
 Charges flow from areas of high potential
energy to areas of lower potential energy.
Potential difference is the difference in
electrical potential energy between two
places in an electric field. This is voltage.
Sec. 20.2, Electric Current & Ohm’s Law
 Voltage
 Voltage
(continued)
is expressed in joules per coulomb.
 The three common sources of voltage are”
Batteries – convert chemical energy into
electrical energy.
Solar cells – convert sunlight into electrical
energy.
Generators – convert mechanical energy
into electrical energy.
Sec. 20.2, Electric Current & Ohm’s Law
 Ohm’s
Law
 Developed
by Georg Ohm (1789-1854)
 Shows the relationship between voltage,
current, and resistance.
 Expressed as V = I x R
V = voltage in volts
I = the product of the current in a circuit in
amps
R = resistance in ohms
Ohm’s Law
V=IR
Voltage
Current
Volts
Amps
Ohms
A
Ω
V
Resistance
Sec. 20.2, Electric Current & Ohm’s Law
 Ohm’s
 In
Law
other words, the voltage in a circuit is equal
to its amperage multiplied by the resistance in
the circuit.
Increasing the voltage increases the current
If voltage is kept constant and resistance is
increased, the current (amperage) is
decreased.
Section 20.2 Quiz

1. A continuous flow of electric charge is
called_________.

2. A flow of current that regularly reverses
direction is called _______ ________.

3. A material that has almost no resistance to
current when cooled to low temperatures is a
____________.
Section 20.2 Quiz

4. Three common sources of voltage are
________, _________, and ________.

5. The potential difference between two places
in an electric field is called _________.

6. name the three components that make up
Ohm’s Law.
Section 20.3, Electric Circuits
 Circuit Diagrams
 An
electric circuit is a complete pathway
through which energy can flow.
 Circuit diagrams use symbols to represent
parts of circuits which include:
 The
complete pathway
 Electrical energy source
 Devices that use the electrical energy
 Switches and junctions
Section 20.3, Electric Circuits
 Types of Circuits
 Series
Circuits
In this circuit, charge has only one path.
If one element stops functioning, the whole
circuit shuts down
Adding components to a series circuit
increases resistance and decreases current,
so the last component gets the least current.
Section 20.3, Electric Circuits
 Types of Circuits
 Parallel
Circuits
Parallel circuits have two or more pathways
through which the current can travel.
With Parallel circuits, one element can fail
and the others will continue to operate.
Parallel circuits are common in homes and
commercial buildings.
Section 20.3, Electric Circuits
 Always remember that when we are talking
about an electrical current, regardless of the
type of circuit, it flows from high potential
to low potential (positive to negative), and
that the electrons flow in the direction
opposite that of the current.
 Check
page.
out the diagram on the following
Section 20.3, Electrical Circuits
 Power
and Energy Calculations
 Electrical
power is the rate at which electrical
energy is converted to another form of
energy.
Electric power is expressed in watts (W) or
the more common kilowatts (kW).
The formula for calculating electric power
is: P (watts) = I (amps) x V (volts)
Section 20.3, Electrical Circuits
Formula for Calculating Electrical Power
P=IxV
Power
(Watts)
W
Current
(Amperes)
A
Voltage
(Volts)
V
Section 20.3, Electrical Circuits
 Problem:
An electric oven is connected to
a 240-volt line. It uses 34 amps of current.
How much electrical power is used by the
oven?
 Formula:
P = I x V (Power = amps x voltage
 Current: 34 amps
 Voltage: 240 volts
 P = ? Watts.
 Plug in the numbers and do the math.
Section 20.3, Electrical Circuits
 Problem
and Energy Calculations
 Calculating
electrical energy lets you know
how much energy is used by an appliance
over time.
 The formula for calculating electrical energy is
E (electrical energy) = P (power) x t (time).
Section 20.3, Electrical Circuits
Formula for Electrical Energy
E=PxT
Electrical Energy
(Kilowatt Hours)
Power
(Watts)
Time
(Hours)
Section 20.3, Electrical Circuits
 Problem:
A clothes dryer that uses 4500
watts of electrical power is operated for 3
hours. How much electrical energy has it
used.
 Formula:
E=Pxt
 P = 4500 watts
 t = 3 hours
 Plug in the values and do the math. How
many kWh (kilowatt hours) would this be?
Section 20.3, Electrical Circuits
 Electrical
 Today
Safety
buildings constructed in the U.S. are
required to have proper wiring, grounding,
fuses, insulation, and circuit breakers.
Fuses and/or circuit breakers prevent
circuits from being overloaded and possibly
starting a fire.
Insulation protects us from short circuits
and electrical shock.
Section 20.3, Electrical Circuits
 Electrical
Safety (continued)
Proper
grounding helps to bleed off excess
current and send it to ground. This can
prevent electrical shock and damage to
appliances
Section 20.3, Quiz
 1.
A __________ _________ is a
complete pathway through which
electrical current can flow.
 2.
The words series and parallel are used to
describe types of what?
 3.
Write out the formula for calculating
electrical power.
Section 20.3 Quiz

4. An electrical circuit which has only one
pathway for current to flow is a/an ______
______.

5. An electrical with two or more pathways for
current to flow is a/an _______ _______.

6. Name 3 safety precautions that building
codes require for house wiring.
Section 20.4, Electrical Devices
 Electronic
Signals
 Electronics
is the science of using electric
current to process or transmit information.\
 Electronic signals are information sent as
patterns in the controlled flow of electrons
through a circuit.
 Electron
flow is controlled by either altering the
voltage or turning the current on and off to
produce the desired signal.
 Electronics
uses digital and analog signals to
convey information with electrical patterns.
Section 20.4, Electrical Devices
 Analog
Signals
 Analog
signals are smoothly varying signals
that are produced by continuously varying the
current or voltage in a circuit.
 Information is encoded in the strength or
frequency of the analog signal.
 AM radio stations are an example of analog
signals.
Notice the smooth contours in the analog
graph of a radio wave in the graph below.
Section 20.4, Electrical Devices
 Digital
 Digital
Signals
signals encode information as a series
of 1’s and 0’s.
 This signal is produced by pulsing the current
on and off.
 Digital signals are more reliable than analog
signals.
Notice the angular shape of the graph
representing digital sound. Remember, you
get digital by switching current on and off.
Comparison
of both
analog (A)
and Digital
(B)
Section 20.4, Electrical Devices
 Vacuum
 This
Tubes
technology was used in early televisions,
computer monitors and other viewing
devices.
 Today, it is rapidly becoming obsolete due to
plasma type devices and digital screens.
 Their size and the fact that they burn out
frequently will soon mark the end of their
usefulness.
Section 20.4, Electrical Devices
 Semiconductors
 Semiconductors
are crystalline solids that
conduct current only under certain
conditions.
 They are made of silicon (Si) or Germanium
(Ge)
 Some
of the purest silicon in the world comes
from the Southern Pines area of N.C.
Section 20.4, Electrical Devices
 Semiconductors
 In
(continued)
pure form, Silicon and Germanium are
poor conductors, but with the addition of
trace amounts of other elements to them, the
current inside the crystals can be controlled.
 By adding trace amounts of boron to silicon,
we can make a p-type (positive)
semiconductor.
 By adding trace amounts of phosphorus to
silicon, we make an n-type (negative)
semiconductor
Section 20.4, Electrical Devices
 Semiconductors
 By
(continued)
themselves, p and n type semiconductors
can’t do much, but when joined together, they
can be very useful in controlling the flow of
electrical current.
Electrons from the n-type are attracted
toward the positive holes of the p-type
semiconductor. The result is what
looks like a positive flow of charge.
Section 20.4, Electrical Devices
 Solid
State Components
 Diodes
are solid state components that
combine 1 n-type and 1 p-type
semiconductor.
When voltage is applied to a diode, the
current will only run from the n-type to the
p-type semiconductor.
This is very useful in directing current.
A diode can change alternating current to
direct current.
Figure A is a diode made
of 2 semiconductors (1 n
and 1 p connected
together. Diodes are two
layers of semiconductors.
Figure B is a transistor
made of 3
semiconductors, 2 n and 1
p sandwiched together.
Transistors are 3 layers of
semiconductors
Section 20.4, Electrical Devices
 Solid-State
 Transistors
Components (continued)
are solid state components with
three layers of semiconductors. Transistors
have two main uses.
As a switch, because a small current
flowing through its center layer can change
its resistance and be used to switch another
current on or off.
As an amplifier, because a small voltage
applied to one side produces a large voltage
on the other.
Figure A is a diode made
of 2 semiconductors (1 n
and 1 p connected
together. Diodes are two
layers of semiconductors.
Figure B is a transistor
made of 3
semiconductors, 2 n and 1
p sandwiched together.
Diodes are 3 layers of
semiconductors
Section 20.4, Electrical Devices
 Integrated
Circuits
 Integrated
circuits, also called chips or
microchips.
 They are a thin slice of silicon that contain
many solid state components.
 They have allowed us to reduce the size of
devices while improving their performance at
the same time.
Section 20.4, Electrical Devices
Section 20.4 Quiz

1. The two types of electronic signals used to
convey information in electric patterns are
_______ and _______.
2. Crystalline solids that conduct electricity only
under certain conditions are called _______.
 3. N-type semiconductors carry a ______
charge, while p-type semiconductors carry a
_____ charge.

Section 20.4 Quiz
4. A _______ is made up of one n-type and 1
p-type semiconductor and can change
alternating current to direct current.
 5. A __________is made up of three layers of
semiconductors, 2 n-type and 1 p-type.
 6. Another name for an integrated circuit is
a/an ___________.
 7. What are the two main elements used in
manufacturing semiconductors?

Section 20.4 Quiz