Transcript electrical

Electricity is one of the most important forms of
energy used in the world today. Without it, there would be
no computers, no television, no lights, and no
communication. People would have to work and live in a
world without many of the conveniences we consider
necessary. Transportation in many areas would be
hampered or not available, such as the lack of street
lights to conduct the flow of traffic. Electricity is
everywhere.
2000 years ago the Greeks discovered that when a
material that we now call amber was rubbed with some
other materials, it became charged with a mysterious
force. The charged amber attracted such materials as
dried leaves and wood shavings. The Greeks called the
amber elektron, which is how the word electricity came
about.
So, what is an electron exactly?
Electron:
negatively
charged
atomic
particle that
moves around
the nucleus of
an atom.
The Cell in Electrical Currents
The cell stores chemical energy and transfers it to
electrical energy when a circuit is connected.
When two or more cells are
connected together, we call
this a battery.
The cell’s chemical energy is
used up pushing a current
around a circuit.
What happens when the cell’s chemical energy is all used up?
The battery dies.
What is an electric current?
An electric current is a flow of microscopic
electrons flowing through wires and components.
+
-
In which direction does the current
flow? from the negative terminal to the positive terminal of
a cell
Simple Circuits
When the switch is closed, the lamp lights up. This is
because there is a continuous path of metal for the
electric current to flow around.
If there were any breaks in the circuit, the current
could not flow.
Circuit Diagram
Scientists usually draw electric circuits using symbols;
cell
lamp
switch
wires
Circuit Diagrams
In circuit diagrams components are represented by
the following symbols;
cell
ammeter
battery
voltmeter
switch
motor
lamp
buzzer
resistor
variable
resistor
Match the circuit symbols to its correct name in your notes.
Electrical Conductors
Are objects that allow electrical charge to flow easily
EMAPLES:
METALS
WIRES
Electrical Insulators
Are objects that do not conduct electricity well
EMAPLES:
FABRIC
PLASTIC
WOOD
Conductor or Insulator?
Cotton balls
INSULATOR
Cookie Sheet
CONDUCTOR
Pennies
CONDUCTOR
Rubber Duck
INSULATOR
Spatula
INSULATOR
Chalk
INSULATOR
Electricity
occurs in 2
forms:
 Static


Is stationary
Examples:



Brush your hair
Wool socks in tumble
drier
Scuff your sock-feet on
thick carpet
 Current


Flows around a circuit
Examples:


Turn on a light
Put a phone on a
charger
Static Electricity
 Occurs with materials
which are insulators
 Rubbing adds or
removes electrons
 Object becomes
charged
 Like charges repel,
unlike charges attract
Current Electricity
 Is the electricity to power
appliances, lights,
computers, etc.
 Requires only a flow of electrons around a
circuit
 Since opposite charges attract and like
charges repel, the electrons are pushed away
from the negative end of the battery or some
other power source and drawn back in at the
positive end creating a circular flow of
electrons.
Circuit Types
The simplest type of circuit involves
electricity going around with no
“choices” (electrons don’t really
choose).
This is called a Series circuit.
Draw the path the electrons
travel.
The other main type of circuit
has two or more branches.
This is called a Parallel circuit.
Draw on the electron flow.
Series Circuits
 Have a single loop for electrons to travel
around
 Components are connected one after another
 Current has to travel through all components
 Current is the same at all points
 Voltage is shared between components
Current in a Series Circuit
2A
2A
2A
The current in a
series circuit is the
same at every point
so the current must
be shared between all
bulbs, making them
dimmer and dimmer
the more you add to
the circuit.
Parallel Circuits
 Have two or more paths for
electrons to flow down
 Current is shared between the
branches
 A PARALLEL circuit has more
than one path for the current to
flow through
 Assuming all bulbs are the same
wattage…they will be the same
brightness
Current in a Parallel Circuit
Advantages of a parallel circuit are:
If one bulb fails ….the other will remain on
Both bulbs can be switched on separately
Resistance
 Resistance is anything
that slows down the
flow of electrons
 Thinner wires offer
more resistance causing
the wire to heat up and
glow (very useful in
light bulb filaments)
 Longer wires also offer
more resistance because
electrons have further to
travel
Power rating of appliances: Figuring your monthly energy bill
Suppose using 100W for 1 hour costs $0.10


How much would it cost to run the space heater
overnight (8 hours)?
How much to run the coffee pot/warmer for 2 hours?
1500w • 8hr = 12,000 watts used
300w • 2h = 600 watts used
12,000 / 100 = 120
600 / 100 = 6
120 • .10 = $12.00 for one night
6 • .10 = $0.60 to run for 2 hrs
Current
Current is the flow of electrons
around a circuit
There are 2 types:
1. DC = direct current =
comes from a battery
o
DC – direct current (battery)
Electrons flow in one direction
AC = alternating current =
comes from electric
companies
2.
o
Electron flow changes direction
50 times per second
AC – alternating current
(generator)
Direct Current (DC)
 Direct Current (DC) always flows in
the same direction, but it may
increase and decrease.
 Electronic circuits (like computers) normally require a
steady DC supply which is constant at one value or a
smooth DC supply which has a very small variation
called ripple.
 Cells, batteries and regulated power supplies provide
steady DC which is ideal for electronic circuits.
 Lamps, heaters and some types of motors will also
work with any DC supply.
Alternating Current (AC)
 Alternating Current (AC) flows one way,
then the other way, continually reversing direction.
 An AC voltage is continually changing between positive (+)
and negative (-).
 The rate of direction change is called the frequency of the AC
and it is measured in hertz (Hz) which is the number of
forwards-backwards cycles per second.
 It is used in power grid transmission and distribution systems
because AC can be easily and efficiently converted from one
voltage to another using a transformer.
Power Grids:
Getting energy from the power plants to your home.
Trace the path from the power plant to a lamp in your
home and put the parts in order.
2 
8 
7 
9 
6 
4 
3 
1 
5 
Transmission Substation
Outlet
Junction Box (on the side of house)
Electric Circuit of a Lamp
Transformer Drum
Power Substation
High Voltage
Transmission Lines
Power Plant
Power Poles
Generating Electricity
 Recall that electricity is just
the flow of electrons.
 To make them flow
(generate electricity), all
you have to do is spin a coil
of wire inside a magnet.
 Of course the larger the coil
and magnets, the more
electricity you can create.
Power Generator
A generator transforms
mechanical energy into
electrical energy
Turbines
 Turbines can spin super large coils through super
large magnets to generate massive amounts of
electricity.
 Power plants usually use steam to turn the turbines.
So what do they burn to boil water and make steam?
Fossil fuels
Producing
Electricity at
a Power Plant
 1. Fuel (fossil fuels) produces heat, which is used to boil
water to make steam.
 2. Steam spins a turbine.
 3. The turbine drives a generator and the generator
makes electricity.
 4. Electricity goes to the transformers to produce the
correct voltage.