Electricity PPt#2

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Transcript Electricity PPt#2

It’s Electric!
Chapter 17
Electricity
Chapter 17
STANDARD
S8P5: Students will recognize
characteristics of gravity, electricity, and
magnetism as major kinds of forces in
nature.
b.Demonstrate the advantages and disadvantages of
series and parallel circuits and how they transfer energy.
c. Investigate and explain that electric currents and
magnets can exert a force on each other.
Chapter 17
WARM-UP
2-22-12
Matter that flows to fit into a container
includes:
A. Solids and liquids
B. Liquids only
C. Gases and solids
D. Liquids and gases
Which phase has the least density?
A. Solid B. Gas C. Liquid
WARM-UP
2-22-12
Which of these factors affects the temperature
at which water boils?
A. The size and shape of the pot in which the
water is heated.
B. The atmospheric pressure at which the
water is heated.
C. The amount of heat added to the water
D. The temperature of the water before it is
heated
WARM-UP
2-22-12
Which of the following occurs when a liquid
becomes a gas?
A. The particles give off energy
B. The particles break away from one another
C. The particles move closer together
D. The particles slow down.
Chapter 17
ESSENTIAL QUESTION
What are the essential
elements of a circuit? ?
Path Finders
Using the
materials at your
table, test each
set-up and
decide which
ones work and
which ones
don’t. Answer
the Path Finders
questions in your
journal.
Chapter 17
CIRCUIT
An uninterrupted
pathway or loop through
which electricity can flow
(usually wire pathway)
Chapter 17
ELECTRIC CIRCUIT
What are the essential
elements of a circuit?
What are the essential
elements of a circuit?
1.An uninterrupted pathway – good
conductor like wires
2.Energy Source – to “push” the
electrons
3.Electrical Device or Load – changes
the electric energy into another form of
energy
Parts of a Circuit
Chapter 17
Parts of an Electric Circuit
• A Switch to Control a Circuit
Sometimes, a circuit also contains a
switch. A switch is used to open and
close a circuit.
Parts of a Circuit
Please note – although
switches are found in my
circuits, they are not an
essential part of a circuit!
Chapter 17
Types of Circuits
• Series
Circuits: A series circuit is a circuit
in which all parts are connected in a single
loop.
• Uses for Series Circuits: Series circuits
are useful in wiring burglar alarms. If any part
of the circuit fails, there will be no current in
the system and the alarm will sound.
Chapter 17
Types of Circuits
• Parallel Circuits: A parallel circuit is
a circuit in which loads are connected
side by side.
• Uses for Parallel Circuits: Almost all
appliances are built with parallel circuits
so that they will keep working if part of
the system fails.
What happens if the
pathway is broken?
The electricity will not
flow… you will have a
“break” in the pathway.
What is a Short Circuit?
An unintended path connecting
one part of a circuit with another.
CONSIDER THIS…
What is the
difference
between static
electricity and
current
electricity?
Chapter 17
RESPONSE…
Static electricity is stationary
or collects on the surface of an
object,
whereas current electricity is flowing
very rapidly through a conductor.
Chapter 17
Why does
Current
Electricity
FLOW?
Chapter 17
Flow of Electricity
#1 Electric charges flow from
an area of high voltage (a lot of
excess electrons) to an area of
low voltage (lower number of
electrons).
What makes the water flow in figure A?
Apply this answer to figure B using negative
charges instead of water.
Water pressure and voltage behave in
similar ways.
Thermal Energy and Electrical
Energy Behave in Similar Ways
Thermal energy flow from high
concentration (warm) to low
concentration (cool) until equilibrium is
reached. Electricity flows from high
concentration (extra negative electrons)
to areas of low concentration (deficient of
electrons = positive area). Both flow from
“high to low”.
Flow of Electricity
#2 The flow of electricity in
current electricity has electrical
pressure or voltage. (Push or
pull from electric force)
Flow of Electricity
#3 Electricity can only flow
when there is a closed
pathway for the charge to
flow through
How Does Electricity Flow?
Current (flowing electrons)
always follow the path of least
resistance.
How is the flow of electricity similar
to the flow of water through a pipe?
Both require a closed path or pipe. If the pipe
is broken or the wire is broken, NO FLOW…
Chapter 17
Circuit Terminology
Essential Terms:
1.Circuit
2.Electrical Current
3.Voltage
4.Resistance
Chapter 17
REMEMBER – a
Circuit is…
An uninterrupted
pathway or loop through
which electricity can flow
(usually wire pathway)
Chapter 17
Electric Current and Electrical
Energy
Electric Current (I)
Rate at which electrical charges
(electrons) pass a given point;
measured in amperes or amps
(A)
Chapter 17
Voltage (V)
Also called Electric Potential
Potential difference between two points in
a circuit
Measured in volts (V)
A measure of how much work is needed to
move a charge (current) between two
points.
Chapter 17
Voltage & Current
As long as there is a voltage between
two points on a wire, charges will flow
in the wire. The size of the current
depends on the voltage. The greater the
voltage is, the greater the current is. A
greater current means that more
charges move in the wire each second.
Chapter 17
Chapter 17
Voltage (V)
Think of voltage as the
amount of energy released as
a charge moves between two
points in the path of a current.
The higher the voltage is, the
more energy is released per
charge
Chapter 17
Resistance (R)
Oposition to the amount of
current in a wire OR “electric
friction”
Measured in ohms(Ω)
Chapter 17
Resistance (R)
Depends on:
a) Type of material
b) Thickness and length of wire
c) Temperature
Chapter 17
Resistance (R)
The resistance of a short, thick
piece of wire is less than the
resistance of a long, thin piece of
wire.
Chapter 17
Resistance (R)
Resistance & Temperature
In general, the resistance of
metals increases as
temperature rises.
Superconductors
If you cool certain materials to
a very low temperature,
resistance will drop to 0 Ω.
Materials in this state are
called superconductors
Superconductors
One interesting property of superconductors is that
they repel magnets. The superconductor in this photo
is repelling the magnet so strongly that the magnet is
floating. Chapter 17, HOLT textbook
Chapter 17
Household Circuit Safety
• Circuit Failure Broken wires or water
can cause a short circuit. In a short
circuit, charges do not go through one or
more loads in the circuit.
• Fuses A fuse has a thin strip of metal.
Fuses keep charges from flowing if the
current is too high.
Chapter 17
Household Circuit Safety, con’t
• Circuit Breakers A circuit breaker
is a switch that automatically opens
if the current is too high. Charges
stop flowing.
• Electrical Safety Tips Do not
overload circuits by plugging in too
many electrical devices. Do not use
electrical devices near water.