Transcript Electricity & Magnetism - Madison County Schools

Electricity & Magnetism
Static, Currents, Circuits
Magnetic Fields & Electro Magnets
Motors & Generators
Jag Mark 11/11/10

What are the three components of an
atom with their respective charges?
Jag Mark 11/12/10

Explain what happens when you get
shocked while touching a metal door knob.
Jag Mark 11/15/10
Compare and contrast AC and DC
currents.
 Compare and contrast circuits in a series
and in parallel.

It’s Electrifying
Each sentence below is about electricity. Complete each
sentence by using the letters that spell the missing word.
(You will not use all of the letters for each word)
1. The unit that measures electric power is the
(k o w a v o t t g e).
2. A conductor has low (o c r e s e l I s I n t a n o r c e),
so electric flows easily through it.
3. When a light switch is off, the circuit broken, or
(c s p o p w e h n).
3. A device that raises or lowers voltage is a
(t h r o a l n s f w o r z a m e r).
The answers are ...
1. The unit that measures electric power is the
WATT
2. A conductor has low RESISITANCE so electric flows
easily through it.
3. When a light switch is off, the circuit broken, or
OPEN
3. A device that raises or lowers voltage is a
TRANSFORMER
Jag Mark 11/17/10
Compare and contrast acids and bases.
 List 2 examples of each.
 Describe how you would determine if a
substance is acidic or basic.

Jag Mark 11/18/10

Outline the pathway that electricity takes
from a power plant to your home.
Jag Mark 11/19/10

Identify 6 forms of energy that may be
used to cause a generator to turn and
generate electricity.
Atoms…
 Have
neutrons, protons, and
electrons.
 Protons are positively charged
 Electrons are negatively charged
Electrons…
 Are
located on the outer edges of
atoms…they can be moved.
 A concentration of electrons in an
atom creates a net negative charge.
(More E than P makes Neg.)
 If electrons are stripped away, the
atom becomes positively charged.
(More P than E makes Pos.)
What is electricity?
The collection or flow of
electrons in the form of
an electric charge
What is static electricity?
When two objects rub against each other electrons
transfer and build up on an object causing it to have a
different charge from its surroundings.
Like the shoes rubbing against the carpet. Electrons are
transferred from the carpet to the shoes.
Static Electricity
 The
build up of an electric charge
on the surface of an object.
 The charge builds up but does not
flow.
 Static electricity is potential
energy. It does not move. It is
stored.
As electrons collect on an object, it becomes negatively
charged. As electrons leave an object it attains a positive
charges. Charges interact with each other:
Have you ever rubbed a balloon on your hair and
stuck it on a wall? How do you think this works?
What causes you to be shocked when you rub your feet
across carpet?
An electrical discharge is the passing of an electric
current through the air from a negatively charged object
to a positively charge object. This is what causes
lightning!
Static vs. Current Electricity
Static electricity is stationary, whereas current electricity
is flowing very rapidly through a conductor.
The flow of electricity in current electricity has electrical
pressure or voltage. Electric charges flow from an area
of high voltage to an area of low voltage.
Water pressure
and voltage
behave in
similar ways.
Electricity that moves…
 Current:
The flow of electrons
from one place to another.
 Measured in amperes (amps)
 Kinetic energy
How can we control currents?
 With
circuits.
 Circuit: is a path for the flow of
electrons. We use wires.
There are 2 types of currents:
Current (DC) – Where
electrons flow in the same
direction in a wire.
 Direct
There are 2 types of currents:
Current (AC) –
electrons flow in different
directions in a wire
 Alternating
Direct current versus alternating
current
AC vs DC : What’s the difference?
Go to this website and click the button for DC
then for AC to visually see the difference
between the two.
You can see that the DC source is a battery –
current flows in one direction. The AC source is
the generator and the current alternates once for
each revolution.
There are 2 types of circuits:
 Series
Circuit: the components
are lined up along one path. If
the circuit is broken, all
components turn off.
Series Circuit
There are 2 types of circuits:
Circuit – there are several
branching paths to the
components. If the circuit is
broken at any one branch, only
the components on that branch
will turn off.
 Parallel
Parallel Circuit
Open circuit Vs. Closed circuit
A closed circuit is one in which the pathway of the
electrical current is complete and unbroken.
An open circuit is one in which the pathway of the
electrical current is broken. A switch is a device in
the circuit in which the circuit can be closed
(turned on) or open (turned off).
Household Wiring
Most household wiring is designed with a
combination of parallel circuits. Electrical energy
enters the home usually at a breaker box or fuse
box and distributes the electricity through multiple
circuits. A breaker box or fuse box is a safety
feature which will open a circuit.
Conductors vs. Insulators
– material through
which electric current flows easily.
 Conductors
– materials through
which electric current cannot
move.
 Insulators
Examples
 Conductors:
 Metal
 Water
pure)
 Insulators:
 Styrofoam
(not
 Rubber
 Plastic
 Paper
What is Resistance?
 The
opposition to the flow of an
electric current, producing heat.
 The greater the resistance, the
less current gets through.
 Good conductors have low
resistance.
 Measured in ohms.
What Influences Resistance?
of wire – aluminum and
copper have low resistance
 Thickness – the thicker the wire the
lower the resistance
 Length – shorter wire has lower
resistance
 Temperature – lower temperature has
lower resistance
 Material
The unit for measuring resistance is the
ohm (Ω).
What is Voltage?
 The
measure of energy given to
the charge flowing in a circuit.
 The greater the voltage, the
greater the force or “pressure”
that drives the charge through the
circuit.
Difference b/t Volts and Amps
 Example
 Amps
– you could say that…
measure how much water
comes out of a hose.
 Volts measure how hard the water
comes out of a hose.
Ohm’s Law
 Resistance
 Ohms
= Voltage / Current
= Volts / Amps
Practice with Ohm’s Law
Ohms
4
15
2
9
6
Volts
100
150
30
45
48
Amps
25
10
15
5
8
Electrical Power
Electrical Power is the product of the current (I)
and the voltage (v)
The unit for electrical power the watt (W)
Example Problem: How much power is used in a circuit
which is 110 volts and has a current of 1.36 amps?
P=IV
Power = (1.36 amps) (110 V) = 150 W
What is magnetism?
Magnetism is the properties and interactions of
magnets.
Magnets produce magnetic forces and have
magnetic field lines
Magnets have two ends or poles, called north
and south poles.
Unlike poles of magnets
attract each other and like
poles of magnets repel.
The earth is like a giant magnet!
The nickel iron core of the earth gives the earth a
magnetic field much like a bar magnet.
Electricity and Magnetism – how
are they related?
When an electric current passes through a wire a
magnetic field is formed.
What is an electromagnet?
When an electric current is passed through a coil
of wire wrapped around a metal core, a very
strong magnetic field is produced. This is called
an electromagnet.
What are electric motors?
An electric motor is a device which changes electrical
energy into mechanical energy.
How does an electric motor work?
We have seen how electricity can produce a
magnetic field, but a magnetic field can also
produce electricity! How?
Moving a loop of wire through a magnetic field
produces an electric current. This is
electromagnetic induction.
A generator is used to convert
mechanical energy into electrical energy by
electromagnetic induction.
Carefully study the next diagrams:
What are batteries?
Batteries are composed of a chemical
substance which can generate voltage which can
be used in a circuit.
Two kinds of batteries: dry cell and wet cell
batteries.
The zinc container of the
dry cell contains
a moist chemical paste
surrounding a carbon rod
suspended in the middle.
(Alkaline and Lithium)
Wet cell batteries are most commonly
associated with automobile batteries.
A wet cell contains two
connected plates made of
different metals or metal
compounds in a
conducting solution. Most
car batteries have a series
of six cells, each
containing lead and lead
oxide in a sulfuric acid
solution.
pH Scale
Measures how acidic or basic a
substance is by its hydrogen ion
concentration
 Ranges from 0 to 14
 A pH of 7 is neutral
 A pH less than 7 is acidic.
 A pH greater than 7 is basic.

Acids vs. Bases

Acids



High hydrogen
[H+] and
hydronium ion
[H3O+]concentrati
on
Taste sour
Ex. Lemon juice,
coke

Bases




High hydroxide ion
concentration [OH-]
Taste bitter
Feel slippery
Ex. Soap, bleach
Strong Acids and Bases
Ionize completely in water
 Good conductors of electricity
 Weak Bond Strength

Indicators

Litmus paper



Acids turn paper red
Bases turn paper blue
Phenolphthalein


Acids are clear
Bases are pink
Neutralization
Acid
 HCL

+
+
Base
NaOH
→
→
Salt +
NaCl +
Water
H 2O
Common Acids
Sulfuric acid: used in car batteries and
used to make paper, detergents,
fertilizer, and paint
 Nitric acid: used to make fertilizers,
rubbers, and plastics
 Carbonic and phosphoric acid: Used in
soft drinks
 Citric acid and ascorbic acid: found in
orange juice
 Hydrochloric acid: stomach acid and
metal production

Common Bases
Sodium Hydroxide: used to make
soap and paper
 Calcium hydroxide: used to make
cement, mortar, and plaster
 Ammonia: used in many household
cleaners and to make fertilizer
 Magnesium hydroxide & Aluminum
hydroxide is used in antacids to treat
heart burn

How is electricity generated?
Most is produced at power plants.
 Turbines with magnets inside are turned
by various energy sources.
 The turbines are surrounded by copper
wire.
 The magnetic field generate by the turbine
causes electrons in the copper wire to
move from atom to atom causing
electricity.

How it gets from plant to places
Electricity leaves the power plant and is
sent over high-power transmission lines on
tall towers.
 Electricity loses some of its strength as it
travels.
 Transformers boost or “step up” its power
to help it along the way.
 Transformers is a device that can increase
or decrease electric voltage.

How it gets from plant to places
When electricity gets closer to its
destination, voltage must be decreased.
 Different transformers then “step down”
the electricity’s power.
 Thinner wires on smaller towers carry the
electricity to homes.

Transformers
 V2/V1
= N2/N1
 As the number of coils increases,
the amount of volts increases.
 As the number of coils decreases,
the amount of volts decreases.
Power Grid

Power plant → substation → “step up”
transformer → transmission lines →
substation → step down transformer →
junction Box → outlet → appliance circuit
Transformers
Fossil Fuels
Hydro Dam
Hydroelectric power
Nuclear power
Wind Power
Tidal Power
Geothermal
Solar
Solar water heating
 Photovoltaic cells
 Solar furnace


http://science.howstuffworks.com/environ
mental/energy/power.htm