Transcript snc2l u3l7 review and quiz

Lesson 7
 Electricity
is a kind of energy. Have you ever
you ever rubbed a balloon on your head and
then stuck it to a wall? If so, you charged the
balloon with electricity.
 The
electrical force that holds a balloon to
the wall is called static electricity. Static
electricity is electricity held in one place on
the surface of an object.

The nucleus contains protons which contain a
positive charge. Neutrons do not have any
charge and are neutral. The electrons contain a
negative charge.

In an object that conducts electricity the
electrons can move freely from atom to atom as
long as they are replaced by another one in their
spot.
In Non-conductors the electrons cannot pass
from atom to atom. This means that if an atom
gains or losses electrons it will contain a
negative or positive charge.

 Think
back to what an atom looks like with
its protons, neutrons and electrons.
 When
you touch a metal
doorknob, for example, electrons
can jump and give you a shock.
Static charges build up on clouds
until they can hold no more. At
that point, lightning can occur.
 The
study of electricity where
the charges are not moving is
called electrostatics
Law of electric charges: Like Charges repel
one another, and unlike charges attract one
another.
 Think of magnets. The opposites attract each
other and the like charges repel each other.
A
static shock can be very powerful, but it is
not very useful. In order to run electrical
devices, we need a steady flow of electricity.
The steady flow of electricity is called an
electric current.
 Electric
current is very similar to a flowing
river. The river flows from one spot to
another and the speed it moves is the speed
of the current. The size of the current flow is
related more to the size of the river than it
is to the speed of the river.
 A river carries more water each second than
a stream, even if both flow at the same
speed. With electricity, current is a measure
of the amount of charge transferred over a
period of time.
A
material that is a good conductor gives
very little resistance to the flow of charge.
This flow of charge is called an
electric current. A good conductor has high
conductivity.
 Metals
are traditional conducting materials.
You see them around the house all of the
time. It's a metal wire or one of the metal
prongs in an electric plug. There are a lot of
free electrons in metallic conductors.
 Free electrons are electrons that are not
being held in atoms, and so, can move easily.
 Some of the best metallic conductors are
copper (Cu), silver (Ag), and gold (Au).
 In
order for electricity to be useful it must be
converted into different forms of energy.
 Electrical energy is converted into the following:




Heat
Light
Motion
Sound (really a component of motion)
 By
wrapping the wire around a metal object
the magnetic field can be magnified. This
will also give the object a distinct North and
South end.


An electric motor is all about magnets and
magnetism: A motor uses magnets to create
motion. So if you have two bar magnets with
their ends marked "north" and "south," then
the north end of one magnet will attract the
south end of the other.
On the other hand, the north end of one
magnet will repel the north end of the other
(and similarly, south will repel south). Inside
an electric motor, these attracting and
repelling forces create rotational motion.
 In
the above diagram, you can see two magnets in the
motor: The armature (or rotor) is an electromagnet,
while the field magnet is a permanent magnet (the
field magnet could be an electromagnet as well, but in
most small motors it isn't in order to save power).
 Fossil
fuel generating stations can use three main
types of fuel; Oil, coal and natural gas. The gas is
burned, and the chemical energy released is used
to heat water and produce steam (1).
 The
high pressure steam is then used to turn a set
of fanlike wheels called turbines (2).
1.
2.
3.
4.
the fuel is burned to boil water to make
steam
the steam makes a turbine spin
the spinning turbine turns a generator
which produces electricity
the electricity goes to the transformers to
produce the correct voltage
 Coal
and oil-fired facilities account for the
majority of air emissions from the electric
power sector.
Emissions
-Carbon
dioxide
-Sulphur
dioxide
-Particulate
matter
Environmental issues due to
pollutants
-Toxic metals - Acid Rain
-mercury
- Smog
- Nitrous
oxides
- toxic substances
-Climate change
 Wind
power is created by using windmills. The wind
turns giant rotors that turn electromagnetic
generators. These generators then send the power
to transformers which then convert the voltage to a
useable amount before it is sent into distribution.
These can now be seen popping up all over Canada.
 The
sun is used to knock elections off atoms.
The electrons flow then creates a current
which must be converted into AC by an
inverter.
 Methane
produced from rotting garbage and
waste is burned. This is then used to heat
water and use the steam to turn a turbine to
create electricity.
 Mechanical
energy can be directly converted
into electrical energy.
 Piezoelectric
crystals can produce small
amounts of energy when they are squeezed
or stretched.
 Thermal
energy can be converted into
electrical energy using a device called a
thermocouple.
 Every
time you use the telephone you are
producing electrical energy as you speak into
the mouthpiece.
 Sound
can be converted into electrical
energy by using piezoelectric crystals or by
moving magnets and electromagnets.
 Solar
cells convert light energy
directly into electricity when
light strikes the surface of
silicon, electrons are released
and produce an electric current.
A
very common source of electrical energy
from a chemical reaction is the voltaic cell.
Every circuit essentially has 4 parts to it.
1. The source of electrical energy
◦
This can range from a battery, to a generation
station.
Electrical Load
2.
◦
Anything that converts electrical energy into
whatever form of energy needed. The load is
the reason that the electrical load exists
3. Connectors
◦
Anything that conducts electricity, this can
include wires to anything that is metal.
4. Electric circuit control device
◦
◦
◦
A simple knife switch, thermostat or any other
device that can control the flow of electricity.
When electricity can make a complete circuit it
is referred to as Closed Circuit
When electricity cannot make a complete
circuit it is referred to as a Open Circuit
 Conductor

or wire
To pass current very easily from one part of a
circuit to another.
 Cell-Supplies

electrical energy
The positive end is bigger than the negative end.
2
Cells
 DC

Source- Electrical energy source
DC = Direct current, always flows one way
 AC
Source - Electrical energy source
 AC = Alternating current, continually
changing direction
 Ground

–
A connection to earth
 Switch
- An on-off switch allows current to
flow only when it is in the closed (on)
position
 Lamp

A transducer which converts electrical energy to
light
 Resistor

A resistor restricts the flow of current,
 Ammeter

-Device that measures current
A
 Voltmeter
 -Device
that measures voltage
V
Motor -electrical load that converts electrical
energy into movement
M
 Voltage
is the electrical force, or "pressure",
that causes current to flow in a circuit. Take
a look at the diagram. Voltage would be the
force that is pushing the water (electrons)
forward. If the water pressure is increased,
more water will flow through the pipe with
more energy.