Download Ch 17 Introduction to electricity

CH 17 INTRODUCTION TO ELECTRICITY
https://youtu.be/EJeAuQ7pkpc
I. ELECTRICAL CHARGE AND STATIC ELECTRICITY
A. ELECTRIC CHARGE
1. All matter is composed of atoms
2. Atoms have 1protons, 2electrons, & 3neutrons
•
Protons (+)
•
Electrons (-)
•
Neutrons (neutral or no charge)
3. Charged objects exert a force
•
Push or pull
4. Law of electrical charges= like charges repel (push away) &
opposite charges attract
5. Protons (+) and electrons (-) attract each other or the atom
would not stay together
6. Electrical force= force of attraction or repulsion on a charged
particle that is die to an electric field
•
Depends on:
1 Amount
of charge on each object (greater the charge=
greater the force)
2
Distance between the charges (closer together= greater
the force )
7. Electrical field= the space around a charged object in which
an electric force is exerted on another charged object
•
Other object will either be attracted or repelled
STOP AND THINK……
• What are 2 types of charged particles in an atom?
• Postive (+) Protons
• Negative (-) Electrons
B. CHARGE IT!
1. An object becomes POSITIVELY charged when it
LOSES electrons
• Losing negatives makes it more positive
2. An object becomes NEGATIVELY charged when it
GAINS electrons
• Gaining negatives makes it more negative
3. Three ways to charge an
object:
a. Friction= electrons are
“wiped” from one object to
another- rubbing a balloon
on your head)
b. Contact (Conduction)=
electrons move from one
object to another by touch
https://youtu.be/T0J5q43MSw8
c. Induction= charges in an
uncharged metal object
are rearranged without
direct contact with a
charged object
C. CONSERVATION OF CHARGES
1. Charges are not created or destroyed when you charge
something by any of the 3 methods
2. The numbers of electrons & protons stay the same
3. Electrons are simply transferred from one object to the next
D. DETECTING CHARGES
1. Electroscope= device that
detects charges
2. Metal strips will hang straight
when it is not charged
3. If a charged object touches
the electroscope the strips
will repel (move apart)
4. Does NOT show if the
charged object is positive or
negative
LAB: CREATING AN ELECTROSCOPE TO DETECT
CHARGES
E. STATIC ELECTRICITY
1. “Static“ = not moving
• Charges of the static electricity do not move away from the
object they are in
2. Static electricity = the electric charge at rest on an object
3. Examples: static cling & charged balloons
• Friction transfers the charge to the clothes or balloon and
since the objects are insulators the charge stays after the
friction ceases
3. Electric Discharge: the loss of electricity as charges move off
an object
https://youtu.be/yc2-363MIQs
a. When you touch a door knob after shuffling your feet
b. Lightening is caused by the large charge difference &
rapid electrical discharge
4. Lightening rods on top of buildings are grounded so the
charge goes into the Earth be absorbed
• Lightening strike the highest point
F. MOVING CHARGES
1. Electrical conductors=
materials in which charges can
move easily
• Most metals
2. Electrical insulators=
materials in which charges
cannot move through easily
• Electrons are held very
tightly in these materials
• Plastic, rubber, glass, wood
& air
3. Semiconductors: special
class of materials that
conduct electric charge
better than electrical
insulators, but not as good
as electrical conductors
• Silicon used in computer
chips
https://www.youtube.com/watch?v=gixkpsrxk4Y&feature=youtu.be
Electricity Review
II. SIMPLE CIRCUITS
A. PARTS OF A CIRCUIT
1. Electrical charges move in a path or circuit
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2. Simple circuit contains:
•
Source of energy (battery)
•
At least one conductor (copper wire)
•
Resistor (light)
•
May contain a switch (closes and opens the circuit)
3. Flow of energy (electrons) go from the negative
end of the battery to the positive end (likes repelopposites attract)
4. Energy in the circuit is called electrical energy
5. Some electrical energy changes to heat
6. Resistors= transform electrical energy to sound,
light, thermal or mechanical energy
•
Light bulb
•
Buzzers
STOP AND THINK
1. Into what forms of energy can resistors transform electrical
energy?
•
Sound, light, thermal or mechanical energy
2. What is the role of insulators such as plastic, rubber, and
cloth covering wires and other conductors in a circuit?
•
Insulators help keep the electric charges inside the
pathway
3. Why aren’t batteries used to supply all power?
•
They could run out of energy
B. CIRCUIT DIAGRAMS
1. Simple circuit diagram= map of a circuit in which the symbols
represent each part of the circuit
2. Volt= measurement of electrical force provided by an energy source
(V)
3. Ohm (Ω) unit of measurement of resistance
4. Current= measure of how much
moves past a given spot
charge
(A) or amp
STOP AND THINK
1. What unit measures resistance to electrical current?
•
Ohm (Ω)
2. What is the difference between volts and amps?
•
volts-= measure of electrical force provided by an energy
source
•
Amp= measure how much current moves past a given spot
each second in a circuit
3. Suppose a series circuit has three bulbs. One burns out.
What will happen in the circuit?
•
The current will NOT be able to flow through and the bulbs
will NOT light
C. SERIES CIRCUITS
1. Current passes through all resistors
2. May have more than one resistor in the circuit
3. The more resistors on the circuit the lower the
current is further down the circuit
III. COMPLEX CIRCUITS
HTTPS://WWW.MSNUCLEUS.ORG/MEMBERSHIP/SLIDESHOWS/ ELECTRICITY.HTML
A. PARALLEL CIRCUITS
1. Parallel circuit has more than one branch or pathway
•
Each branch may hold several resistors where
electrical energy can be put to work
2. Not all branches have to be on at the same time for the
current to flow
•
Useful= you don’t have to have the light on in the
kitchen to have the refrigerator running
STOP AND THINK
1. Name two advantages of parallel circuits over
series circuits
•
Parallel circuits have more than 1 branch and
not all branches need to be on at the same time
2. What is an example of a parallel circuit in your
home?
•
Lights in the room and the TV= many others
3. If one conductor on the computer chip is open,
will the computer shut down?
•
No, the chip uses parallel circuits with millions
of paths
LESSON 4 MAGNETS & MAGNETISM
A. PROPERTIES OF MAGNETS
1. Magnetic Force: the push or pull force resulting when two
magnets are placed close to each other
• Results from spinning electric charges in the magnets
• Can act from a distance
2. Magnetic Poles: one of two ends of a magnet that have
opposing magnetic qualities
• North and south poles
• Opposites attract & likes repel
3. Magnetic fields: area surrounding a magnet where
magnetic forces can be detected
• Strongest near the poles
• Greater the distance from the poles the weaker the
magnetic field
Temporary Magnet Mini lab
1. Get a normal paperclip. What happens to the compass
& the metal filings when the paperclip was put over it?
2. How will you magnetize the paperclip?
3. What happens to the compass and the metal filings
after the paperclip is magnetized?
4. Draw the domains on the paperclip before and after
magnetism
B. WHAT CAUSES MAGNETISM?
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1. The charged electrons in the atom of the magnetic object do
NOT fully cancel each other out
•
Result is that these materials will have a magnetic field with
2 magnetic poles (north & south)
•
No matter how many times you cut the magnet, it will
continue to have 2 poles
2. The formation of domains lined up
makes a strong magnetic field
•
Domain= tiny magnetic areas
formed by group of atoms in an
object whose electrons do not fully
cancel out
•
When the domains line up in the
same direction they form a strong
magnetic field together around the
entire object
C. TYPES OF MAGNETS
1. Ferromagnets= materials that can be turned into a magnet
• Iron
• Nickel
• Cobalt
2. Electromagnets= iron core wrapped with electrical wire in which
an electric current runs through the wire
• When the electric current is turned on it is a strong magnet
• When the electric is off the object the magnetic field stops
3.
Temporary magnets= materials such as iron can be made into
a magnet for a short period of time by using another magnet to
line up the domains
• Over time it will lose magnetism
D. THE EARTH IS A GIANT MAGNET
1. The liquid outer core of the Earth is made of iron and nickel which
creates a magnetic field when the Earth is in rotation
•
Stronger near the poles
•
The outer core is moving so the magnetic pole will change
slightly overtime
2. The Earth has magnetic poles, but they are not exactly the
geographic north and south pole
•
A compass has a “north seeking” pole and a “south seeking”
pole
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3. Auroras= charged particles
interacting with atoms in the
atmosphere causing the atoms
to emit visible lights.
a. The type of particles will
produce different colors
 Oxygen= greenish
yellow or red
 Nitrogen= blue or deep
red
b. Aurora Borealis= Northern
Hemisphere
c. Aurora Australis= Southern
Hemisphere
LESSON 5 ELECTROMAGNETISM
A. ELECTROMAGNETS
HTTPS://YOUTU.BE/SMB1DSIJCUQ ELECTROMAGNET
1. Electromagnetism= results when electric currents and
magnetic fields interact with each other
2. 1820 Danish professor Hans Christian Oersted noticed when
he brought a compass close to the electric current the needle
of a compass moved
3. Every electrical current produces a magnetic force
4. Solenoid= a coil of wire that carries an electric current
producing a magnetic field
5. Electromagnets= wrapping a solenoid around an iron core
•
Combines the magnetic field of the solenoid with the magnetic field
of the magnetized iron core
6. Electromagnets can be used to lift or move very heavy
objects
• Easy to turn on to lift and off to drop
7. To increase the strength of the electromagnet you can;
a. Increase the current
b. Increase the number of coils
c. Add iron core
d. Layer the coils
http://study.com/a cademy/lesson/how-magnetic-fields-are-created.html
8. Galvanometer= device used that measures the
strength and direction of an electric current in a wire
9. Electromagnets are used in MRI machines to take
more detailed pictures of the inside of a person than
xrays
• Has to be super cooled to get the strongest
magnetic field possible (reduces friction)
STOP AND THINK
1. How was electromagnetism discovered?
•
Hans Christian Oersted noticed when he
turned on an electric current the needle on
the compass moved
2. Why is the ability to turn off an electromagnet
advantageous?
•
There are times that it is not needed or to
move heavy metal objects
B. HOW DO MOTORS WORK?
1. Electric motor= changes electrical energy into
mechanical energy
• Can run on AC or DC current
2. Electric motors use electromagnets
• A simple motor has an armature (coil or loop of wire)
mounted between poles of a magnet
• The armature (wire) is pushed and pulled
• The commutator will change the direction of the
current allowing the armature to make a complete
rotation
C. ELECTROMAGNETIC INDUCTION
1. 1830s Michael Faraday discovered that when a
magnet was moved inside a metal coil it created
an electric current
2. Electromagnetic induction= using a magnetic field
to create an electric current
D. CHANGING VOLTAGE
1. Transformers use induction to increase or decrease
the voltage of alternating current
• Iron “rings” with two coils of wire
• The more coils the wire makes the higher the
voltage and vice versa
2. Transformers on powerlines increase voltage to
send it many miles away then decrease it to safe
levels before sending it into a home
DO THE MATH PAGE 463
• Get with a partner and do the calculation on the page
by first multiplying the primary side volts by the
secondary sides turns. Then divide the answer from
above by the primary side turns.
• SHOW YOUR RAITO SET UP
• You may use a calculator for the math but you have to
show the set up like the example in the book
• One volunteer put it on the board
E. ELECTRICAL GENERATORS
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1. Electrical generators use induction to change mechanical
energy into electrical energy
•
Generators are opposite of electrical motors
2. Generators induce electric current when a magnet moves
in a coil of wire or when a wire moves between the poles
of a magnet
3. Review: https://youtu.be/gixkpsrxk4Y
ASSIGNMENT DUE MONDAY
1. Read 580-466
2. Answer questions 1-27 omitting #4, 10,& 17
3. ALSO pg 467 1-12
4. If you are quiet you may have partners for 1-27
5. NO PARTNERS for 1-12