Transcript Electricity PPT

Chapter 17
BRAINSTORMING
•On a clean journal page write
today’s date and the title …
“BRAINSTORMING”
Now write/draw as many facts
about electricity as you can. You
have 3-4 minutes only
Chapter 17
WARM-UP 2/10/2012
1. Get your journals and have a seat
2. Please complete the Phase Change
Review Paper
Warm – Up
Phase Change Graph Review
Chapter 17
WARM-UP 2/13/2012
1. Get your journals and have a seat
2. We will be taking a Pre-Quiz today
3. Tape the reading passage into your
journal
Student Led Demo
“Snap, Crackle, Jump”
2/13/2012
Vinyl Albums are “old fashioned” form of
popular music. Watch what happens
when I rub the vinyl and then hold it over
the rice krispies…
Chapter 17
Student Investigation
“Rub a Balloon”
2/13/2012
1. Each group has an investigation
kit at their table
2. Each student is responsible for
completing their own lab sheet
Chapter 17
Warm-Up
2/14/2012
1. You will need your journal
2. Complete Warm Up Worksheet
***Activities #25-#26***
3. Tape into your journal
Chapter 17
Warm-Up
2/15/2012
3-2-1
In your journal’s write down:
3 Things you learned from yesterday
2 Question’s you have
1 Guess at what we will be doing
today!
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
ESSENTIAL QUESTION
What is electrical energy?
Chapter 17
Electric Charge
Charges Exert Force Atoms are
composed of particles with
electric charge. The law of
electric charges states that like
charges repel and opposite
charges attract.
Chapter 17
Matter Review
Matter is made up of
small particles called
atoms.
Chapter 17
Electric Charge
Protons have
a positive
charge
Electric charge is a property that
allows an object to exert a force
another object without touching it.
The Force Between Protons and
Electrons Because protons and
electrons have opposite charges, they
are attracted to each other.
Electrons have
a negative
charge
Electric Force
The force between charged
objects is an electric force. It is
the force (a push or a pull) on a
charged object due to an
electric field Note: Like charges
push Unlike charges pull
Electric Field
•An Electric Field is the
region around a charged
object in which another
charged object experiences
an electric force
Law of Electric charges
Like charges will repel (push
away) each other and unlike
charges will attract (pull toward)
one another
Law of Electric charges
The force (a push or a pull) on a
charged object due to an electric
field Note: Like charges push
Unlike charges pull
Chapter 17
Chapter 17
Remember…
Most objects have approximately
the same number of protons and
electron. They have no electrical
charge.
They are neutral
Chapter 17
So How do Objects
Become Charged?
Objects can become charged when
electrons are transferred by:
1. Conduction
2. Induction
3. Friction
Chapter 17
Charge It!
• Friction
Charging by
friction happens when
electrons are “wiped” from
one object
onto another.
Chapter 17
Charge It!
•Conduction Charging by
conduction happens when
electrons move from one
object to
another
by direct
contact.
Chapter 17
Remember…
Like thermal energy, which
flows from more energy to
less, electric energy will flow
from area that has more
charges to an area with less
charges. Charge will move
until equilibrium is reached.
Chapter 17
Charge It!
Induction - movement of
electrons to one part of an object
because of the influence of the
electric field of another object
Charges can move between two objects that are touching
Chapter 17
Charge It!
When a charge object is brought nearby, one charge is
attracted to the object and the other charge is repelled
by the object.
Chapter 17
Charge It!
The two objects are separated while the charged rod is
still nearby. Now apart, charges can no longer move
from one object to the other.
Chapter 17
Charge It!
Charged object is removed from the area. Two objects
are now oppositely charged. What would happen if the
two object were moved so they were touching again?
Charge It!, continued
Static Electricity
Electrical
charge at rest
on an object
Electrical Discharge
The release
of electricity
stored in an
object
Key Concept…
When a negatively charged
object comes close to a positively
charged object, electrons move
to neutralize the charge
Key Concept Continued
Key Idea continued If a
neutral state (charge of zero)
can not be reached, electrons
will move until the number of
excess electrons or protons
is the same on both objects.
Familiar Static…
Lightning – positive
charges collect at
the top of a cloud;
Negative charges
collect at the
bottom of the cloud
.
Chapter 17
Lightning Danger!!!
Lightning Dangers It is particularly
dangerous to be at the beach or on a
golf course during a lightning storm.
Even standing under a tree during a
storm is dangerous.
Thunderstorm clouds’ negative
charges are usually attracted to the
highest nearby positive object – YOU!
Chapter 17
Lightning Rods
A lightning rod is a
pointed rod
connected to the
ground by a wire.
Objects that are
joined to Earth by
a conductor, such
as a wire, are
grounded.
Chapter 17
Detecting Charge
You can use a
device called
an electroscope
to see if
something is
charged.
Chapter 17
Moving Charges
Conductors An electrical
conductor is a material in which
charges can move easily.
Insulators An electrical insulator
is a material in which charges
cannot move easily.
Chapter 17
Electric Current
• Electric current is the rate at which charges
pass through a given point. Electric current is
expressed in units called amperes, or amps.
• Making Charges Move When you flip a
switch, an electric field is set up in the wire at
the speed of light. The electric field causes the
free electrons in the wire to move.
Chapter 17
Electric Current, continued
• Commanding Electrons to Move This electric field
is created so quickly that all electrons start moving
through the wire at the same instant. Think of the
electric field as a command to the electrons to charge
ahead.
Chapter 17
Electric Current, continued
• AC and DC There are two kinds of electric
current—direct current (DC) and alternating current
(AC).
Chapter 17
Voltage
• Voltage is the potential difference between
two points in a circuit. Voltage is expressed in
volts (V).
• Voltage and Energy Voltage is a measure of
how much work is needed to move a charge
between two points. You can think of voltage
as the amount of energy released as a charge
moves between two points in the path of a
current.
Chapter 17
Electric Current and Electrical
Energy
Voltage, continued
• Voltage and Electric
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.
• Varying Nature of Voltage
Different devices need
different levels of voltage.
Chapter 17
Resistance
• Resistance is the opposition to the flow of electric
charge.
• Resistance and Material Good conductors, such as
copper, have low resistance. Poor conductors, such as
iron, have higher resistance.
• Resistance, Thickness, and Length Thick, short
wires have less resistance than thin, long wires.
Chapter 17
Resistance, continued
• Resistance and Temperature In general, the
resistance of metals increases as temperature rises.
Chapter 17
Generating Electrical Energy
• Parts of a Cell A cell contains a mixture of
chemicals called an electrolyte. Every cell also
has a pair of electrodes made from conducting
materials.
• Kinds of Cells Two kinds of cells are wet
cells and dry cells. The electrolytes in dry cells
are solid or pastelike.
Chapter 17
Chapter 17
Generating Electrical Energy, continued
• Thermocouples
Thermal energy can be
converted into electrical
energy by a
thermocouple.
• Photocells A photocell
converts light energy into
electrical energy.
Chapter 17
Connecting Current, Voltage, and Resistance
• Georg Ohm (1789 –1854) studied the resistances of
materials. He measured the current that resulted from
different voltages applied to a piece of metal wire.
• Ohm’s Law Ohm found that the ratio of voltage to
current is a constant for each material. This ratio is the
resistance of the material.
Chapter 17
Connecting Current, Voltage, and Resistance,
continued
Chapter 17
Chapter 17
Electric Power
• What Is Electric Power? The rate at which electrical
energy is changed into other forms of energy is electric
power. Electric power is calculated using the following
equation:
power  voltage  current, or P  V  I
• Watt: The Unit of Power The unit for power is the
watt (W). Another common unit of power is the
kilowatt (kW). One kilowatt is equal to 1,000 W.
Chapter 17
Electric Power, continued
• Power Ratings When you
read the wattage label on a light
bulb, you are reading the bulb’s
power rating. The power rating
describes the rate at which an
electric device uses electrical
energy.
Chapter 17
Measuring Electrical Energy
• The amount of electrical energy used in a home
depends the power of the electrical devices in the
house and the length of the time that those devices
are on. The equation for electrical energy is as
follows:
electrical energy  power  time, or E  P  t
Chapter 17
Chapter 17
Measuring Electrical Energy, continued
• Measuring Household Energy Use Different
amounts of electrical energy are used each day in a
home. Electric companies usually calculate electrical
energy by multiplying the power in kilowatts by the
time in hours.
• How to Save Energy Every appliance uses energy.
Replacing items that have high power ratings with
items that have lower ratings is a way to save energy.
Chapter 17
Measuring Electrical Energy, continued
• It’s All About the Bulb All of the lighting in a home
could make up as much as 25% of a home’s energy
consumption. So, buying and using energy–efficient
light bulbs can make a big difference in the amount of
energy used by a household.
• Energy–Saving Programs Many governments and
organizations around the world have started programs
to help save energy and natural resources.
Chapter 17
Parts of an Electric Circuit
• Forming a Loop An electric circuit is a complete,
closed path through which electric charges flow.
• All circuits need three basic parts: an energy source,
wires, and a load.
Chapter 17
Section 4 Electric Circuits
Chapter 17
Section 4 Electric Circuits
Parts of an Electric Circuit, continued
• A Switch to Control a Circuit Sometimes, a circuit
also contains a switch. A switch is used to open and
close a circuit.
Chapter 17
Section 4 Electric Circuits
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
Section 4 Electric Circuits
Types of Circuits, continued
• 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.
Chapter 17
Section 4 Electric Circuits
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
Section 4 Electric Circuits
Household Circuit Safety, continued
• 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.