Transcript chapter 17 for weebly

Electricity
Chapter 17
Electric Charge & Static Electricity
A buildup of static electricity can cause
little “shocks”
This is from an electric charge.
Charges:



Charged objects exert a force on other
charged objects
Two types of charges are positive and
negative charges.
Like charges repel & opposite charges attract.
Electric Force & Electric Field
The force between charged objects is an
electric force.

Strength of force is determined by size of charges,
and distance between the objects.
The electric field is a region around a charged
particle that can exert a force on another
charged particle.

If a charged particle is in the electric field of another
charged particle, the first particle is attracted or
repelled by the electric force.
Charging Atoms
Atoms can become charged by gaining or
losing electrons.


If an atom loses electrons, is it positively or
negatively charged?
What about if an atom gains electrons?
Using friction to charge objects
Friction can cause
electrons to be “wiped”
from one object and
transferred to the other
(for example rubbing a
balloon against your
hair).
Using conduction to charge objects
Charging by
conduction happens
when electrons are
transferred from one
object to the next by
direct contact (for
example touching a
negatively charged
plastic ruler to an
uncharged metal rod)
Charging by induction
This occurs when
charges in an
uncharged object are
rearranged without
direct contact with a
charged object.
For example a
negatively charged
balloon that is close to a
neutral wall will repel the
electrons away from it.
Conservation of
charges:

When you charge
objects by any
method, no charges
are created or
destroyed
Detecting charge:

A device called an
electroscope can
determine if an object
has a charge.
Conductors
A conductor is a
material in which
charges can move
easily.
Most metals are good
conductors because
some of the electrons in
metals are free to move
about.

Copper, silver, and
aluminum
Insulators
An insulator is a
material in which
charges cannot easily
move.
In insulators electrons
are tightly bound to
the atoms and cannot
flow freely.

Plastic, rubber, glass,
wood
Static Electricity
Static Electricity is the
buildup of electric
charges on an object.
Static means not
moving: the charges
that create static
electricity do not move
away from the object
that they are stuck to.
Electric Discharge
Electric Discharge is when the charges that
build up as static electricity on an object
eventually leave the object.
Sometimes this happens slowly (clothes stuck
together will eventually transfer electrons to
water molecules in the air)
Sometimes this happens quickly and may be
accompanied by a flash of light, shock, or
cracking noise.
Give an example of an electric discharge…
Lightening
This is a dramatic example
of electric discharge.
Benjamin Franklyn first to
discover lightening as a
form of electricity, he also
developed the lightening rod
( a pointed rod connected to
the ground by a wire).
What are some dangers of
lightening?
Electrical Energy
Electrical Energy is the
energy of electric charges.
Electrical energy provides
people with many comforts
and conveniences, such as
being able to watch tv, turn
on a light…etc
One common way to
produce electric current is
through chemical reactions
in a battery.
Batteries & Cells
A cell is a device that
produces an electric current
by converting chemical
energy into electrical energy.
A battery converts chemical
energy into electrical energy
and is made up of several
cells.
Every cell contains a mixture
of chemicals that conduct a
current. These are known as
electrolytes.
Cells cont.
Cells also contain
electrodes.
Electrodes are the
parts of cells where
charges enter or
exit.
Types of Cells
Wet Cells:


Contain liquid electrolytes
Car Batteries are examples
Dry Cells:

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Contain electrolytes that
are solid or pastelike
Portable radio cells, and
flashlights are examples of
these.
Potential Difference
Potential Difference
is the energy per
unit of charge.
It is measured in
volts.
The greater the
potential difference
the greater the
current.
Photocells and Thermocouples
These are two other ways
that electric energy can
be converted.
Photocells:

Part of solar panel that
converts light to electric
energy.
Thermocouples:

Think “thermal”. Uses
thermal energy to convert
to electrical energy.
Quiz 17.1
1. The type of cell that contains liquid
electrolytes are
a. Wet Cells
b. Dry Cells
2. The buildup of an electric charge in an
object is known as:
a. electric current
c. conductors
b. static electricity
d. insulators
3. ________ converts chemical energy into
electrical energy. (battery or photocell)
Quiz 17.1
1. An object becomes charged when the
atoms in the object gain or lose:
a. Protons
c. Electrons
b. Neutrons
d. All of the above
2. If two charges repel each other the two
charges must be:
a. positive and positive
b. positive and negative
c. negative and negative
d. either (a) or (b)
Electric Current
Current is the rate at which charge passes a
given point.
The unit for current is ampere “amp” (A)
The two types of electric current are (AC)
alternating current and (DC) direct current.
In AC the charges continually switch from
flowing in one direction to the reverse.

Outlets in your home
In DC the charges always flow in the same
direction.

Current from batteries and cells
Voltage
The current in a wire is
determined by voltage.
Voltage is the difference
in energy per unit of
charge as it moves
between two points in
the path of a current.
Voltage is another word
for potential difference.
Voltage can vary
Electrical voltage in
U.S. for electrical
outlets usually supply a
voltage of 120V, where
a portable radio only
needs 3V they run
easily on batteries.
Did you know that
electric eels can create
a voltage of 600 V!!
Resistance
Resistance (R) is the opposition to the flow of
electric charge, and is expressed in ohms.
Think “electrical friction”
Good conductors = low resistance
Good insulators = high resistance
Resistance is also effected by thickness and
length of wires, and also by temperature.
Ohm’s Law
German school teacher Georg Ohm
determined that the relationship between
current (I), voltage (V) and resistance (R)
could be expressed with the following
equation:
amperes = volts
ohms
Electric Power
Electric Power is the rate at which electrical
energy is used to do work.
Power = voltage x current
P=VxI
In units: watts (W) = volts (V) x amperes (A)
Watts the difference???
Watt is the difference between a 60W light
bulb and a 120W light bulb?
Answer: As power increases the bulb
burns brighter, so 120W will be brighter
than 60W
Electric Circuits
A circuit is a
complete closed path
through which
electrical charges
flow.
Circuits contain an
energy source
(battery), a load (light
bulb), and wires to
connect the two
together.
Types of Electric Circuits
Series Circuits: all parts
are connected in a single
loop
Parallel Circuits: different
loads are located on
separate branches, and
charges will travel
through more than one
path. Most household
circuits are parallel.
Quiz 17.2
1. Charges flow easily in a(n) _______
(insulator, conductor)
2. _________ is the opposite to the flow of
electric charge. (Resistance, Electric
power)
3. A ________ is a complete closed path
through which charges flow (load, circuit)
Quiz 17.2 cont.
1. What type of current comes from the outlets in
your home?
a. direct current
b. alternating current
c. electric discharge d. static electricity
1. What are the three parts of a circuit?
a. energy source, load, wires
b. energy source, electricity, battery
c. energy source, conductors, wires
d. electricity, insulators, battery