Download Chapter 20 Notes

Static Electricity
Electrical Charge:
Is a concentration of
electricity
Unlike Charges
Attract one another
Like Charges
Repel one another
Electric Fields
The effect an electric charge has
on other charges in the space
around it.
Strength of Electric Field
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Amount of charge that produces the
field
And the distance from the charge
Static Electricity and
Charging
Static electricity: is the study of
the behavior of electric charges,
including how charge is
transferred between objects.
Charges can be Transferred

Friction
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Contact
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Induction
Charging by Friction
Transferring of electrons
Charging by Contact
Charging by contact occurs when
someone actually touches another
object and the electrons are then
transferred (Van de Graaf Generator)
Charging By Induction
A transfer of charge without
contact between materials.
Static Discharge
Occurs when a pathway through
which charges can move forms
suddenly. An example would by
lightning.
Electric Current & Ohm’s Law
Electric Current
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The rate at which charges flows
through the lamp or wires.
Current: is how much electric
charge flows past a pint in a circuit
during a given time.
Current is measured in ampes.
Two Types of Current

Direct Current (DC)
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Alternating Current (AC)
Direct Current
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Charge flows in one direction
An example would be a flashlight or
most battery powered devices.
Alternating Current
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Is a flow of electric charge that
regularly reverses its direction.
Electric current in your home and
schools are like this.
Conductors and Insulators
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Electrical Conductor
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Electrical Insulator
Electrical Conductor
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Is a material through which charge
can flow easily
For example: copper; silver; and
most metals
Electrical Insulator
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A material through which a charge
cannot flow through easily.
For example: Wood; Plastic; rubber;
and air
Resistance
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Is the opposition to the flow of
charges in a material.
The S.I. unit of resistance is Ohm.
A materials thickness, length, and
temperature affect its resistance.
Superconductor
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Is a material that has almost zero
resistance when it is cooled to low
temperatures.
The best superconductor so far is
cooled to 138 K.
Voltage

In order for charge to flow in a
conducting wire, the wire must be
connected in a complete loop that
includes a source of electrical energy.
Voltage


Potential Difference: is the
difference in electrical potential
energy between two places in an
electrical field.
It is measured in joules per coulomb,
or volts, it can also be known as
voltage.
Voltage Sources

Batteries

Solar Cells

Generators
Voltage Sources

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Battery: is a device that converts
chemical energy to electrical energy.
Have terminals that can connect to
wires in a circuit.
One terminal is positive and the
other is negative.
Ohms Law

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Founded by German Scientist Georg
Ohm.
First determined how resistance and
current affect voltage.
Discovered that voltage is not the
same everywhere in a circuit.
Hypothesized that resistance reduces
the voltage.
Ohm’s Law

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Ohm’s Law: the voltage (V) in a
circuit equals the product of the
current (I) and the resistance (R).
V = I x R or I = V/R
Increasing the voltage increases the
current. Keeping the same voltage
and increasing the resistance
decreases the current.
Circuit Diagrams

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Electric Circuit: A complete path through
which charge can flow.
Ex. Wiring in a house
Circuit diagrams use symbols to represent
parts of a circuit, including a source of
electrical energy and devices that are run
by the electrical energy.
Circuit Diagrams

Circuit diagrams shows one or more
complete paths in which a charge
can flow.
Series Circuits

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Series Circuit: charge has only one
path through which it can flow.
Ex. Christmas Tree Lights
If one element stops functioning in a
series circuit, none of the elements
can operate.
Parallel Circuits
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Parallel Circuit: is a electric circuit
with two or more paths through
which charges can flow.
If one element stops functioning in a
parallel circuit, the rest of the
elements still operate.
Power & Energy Calculations
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Electric Power: the rate at which electrical
energy is converted to another form of
energy.
The unit is Watt or joules per second
Power is often measured in KiloWatts.
Electric power can be calculated by
multiplying voltage by current
Power and Energy Calculations

Electric Power

P (Watts) = I (Amps) x V (volts)
Electrical Energy

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E=Pxt
This equation is used to find the
electrical energy used by an
appliance.
Electrical Safety

Correct wiring, fuses, circuit
breakers, insulation, and grounded
plugs help make electrical energy
safe to use.
Home Safety

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Fuses: prevents current overload in
a circuit.
Circuit Breakers: is a switch that
opens when current in a circuit is too
high.
Personal Safety

Grounding: when the electric takes
a shorter path to a wire which leads
to the ground. This is a transfer of
excess charge through a conductor.
Electronic Devices
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Electronic Signals
Vacuum Tubes
Semiconductors
Solid-State Components
Communications Technology
Electronic Signals
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Electronics: the science of using
electric current to process or
transmit information.
Electronic Signal: is information
sent as patterns in the controlled
flow of electrons through a circuit.
Electronic Signals
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Electronics conveys information with
electrical patterns called analog and digital
signals.
Analog Signal: is a smoothly varying
signal produced by continuously changing
the voltage or current in a circuit.
• Information is encoded in the strength or
frequency of the analog signal.
Electronic Signals
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Digital Signal: encodes information
as a string of 1’s and 0’s.
Digital Signal is like Morse Code,
when the current is off it produces a
0 and when it is on it produces a 1.
Digital is more reliable than analog.
Vacuum Tube
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Controls the flow of electrons in early electronic
devices.
Vacuum tubes can change alternating
current into direct current, increase the
strength of a signal, or turn a current on or
off.
Example: TV tubes
Problem: burn out frequently and need replaced.
They are also too large for small devices.
Semiconductors
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Semiconductor: is a crystalline solid
that conducts current only under certain
conditions.
• Made with silicon or germanium
• Two types of conductors
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N-type: current flows as electrons
P-type: current flows as positive charge.
When the two conductors are joined electrons from
the n-type are attracted to the positive p-type
conductor.
Solid-State Components

Most modern electronic devices are
controlled by solid-state components.
• Diodes
• Transistors
• Integrated Circuits
Diode
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Combines n-type conductor and ptype semiconductor.
• Changes alternating current into direct
current.
Transistors
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Has three layers of semiconductors.
Current flowing through its center
layer changes its resistance.
• Can be used a switch, because the small
current can turn another current on or
off.
• Can be used as an amplifier
Integrated Circuits
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A thin slice of silicon that contains
many solid-state components.
• Commonly known as chips or microchips
• Used in pages, mobile phones, and
computers.
Communications Technology

Computer: programmable device
that can store and process
information.
• Communication devices use microchips
to make them more portable, reliable,
and affordable.