Transcript Electric Current

Conceptual Physics
11th Edition
Chapter 22:
ELECTROSTATICS
© 2010 Pearson Education, Inc.
Chapter 22
Chapter Objectives
• Electrical Forces and
Charges
• Conservation of Charge
• Coulomb’s Law
• Conductors and
Insulators
• Charge Polarization
• Electric Field
• Electric Potential
• Electric Energy Storage
© 2010 Pearson Education, Inc.
Warm-Up
• If the electrons around an
atom’s nucleus are
spinning then why don’t
they just fly off?
© 2010 Pearson Education, Inc.
Electricity= electrical
phenomena
At rest =
electrostatics =
ch 22
Current & magnetism
= Ch 24
Electrical current
“charges” = Ch 23
© 2010 Pearson Education, Inc.
Using electricity and
magnetism = Ch 25
Electric Force and Charges
CHECK YOUR NEIGHBOR
When you brush your hair and scrape electrons from your
hair, the charge of your hair is
A.
B.
C.
D.
positive.
negative.
Both A and B.
Neither A nor B.
© 2010 Pearson Education, Inc.
Electric Force and Charges
CHECK YOUR ANSWER
When you brush your hair and scrape electrons from your
hair, the charge of your hair is
A.
B.
C.
D.
positive.
negative.
Both A and B.
Neither A nor B.
Comment:
And if electrons were scraped off the brush onto your hair, your hair
would have a negative charge.
© 2010 Pearson Education, Inc.
Coulomb’s Law
Charge polarization
• Atom or molecule in which the charges are aligned with
a slight excess of positive charge on one side and slight
excess of negative charge on the other
• Example: Rub an inflated balloon on
your hair and place the
balloon on the wall. The
balloon sticks to the wall
due to charge polarization in
the atoms or molecules of
the wall.
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Conservation of Charge
Conservation of charge
• In any charging process,
no electrons are created
or destroyed. Electrons
are simply transferred from
one material to another.
• Tape demo
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Coulomb’s Law
Coulomb’s law
• This formula describes the transfer (electrical
force)
Differences between gravitational and
electrical forces
• Electrical forces may be either attractive or repulsive.
• Gravitational forces are only attractive.
© 2010 Pearson Education, Inc.
Coulomb’s Law
Coulomb’s law (continued)
• If the charges are alike in sign, the force is
repelling; if the charges are not alike, the force is
attractive.
• In equation form:
q1q2
k = 9,000,000,000 Nm2/C2
F=k 2
d
• Unit of charge is coulomb, C

• Similar to Newton’s law of gravitation for masses
• Underlies the bonding forces between molecules
© 2010 Pearson Education, Inc.
Coulomb’s Law
CHECK YOUR NEIGHBOR
According to Coulomb’s law, a pair of particles that are
placed twice as far apart will experience forces that are
A.
B.
C.
D.
half as strong.
one-quarter as strong.
twice as strong.
4 times as strong.
© 2010 Pearson Education, Inc.
Coulomb’s Law
CHECK YOUR ANSWER
According to Coulomb’s law, a pair of particles that are
placed twice as far apart will experience forces that are
A.
B.
C.
D.
half as strong.
one-quarter as strong.
twice as strong.
4 times as strong.
Practice Coulomb’s Law Worksheet
© 2010 Pearson Education, Inc.
Chapter 22
Chapter Objectives
• Electrical Forces and
Charges
• Conservation of Charge
• Coulomb’s Law
• Conductors and
Insulators
• Charge Polarization
• Electric Field
• Electric Potential
• Electric Energy Storage
© 2010 Pearson Education, Inc.
Warm-Up
• Get out HW then answer
the following
• Give an example of a
conductive material.
• Give and example of an
insulating material
Conductors and Insulators
• Conductor: Materials in which one or more of the
electrons in the outer shell of its atoms are not
anchored to the nuclei of particular atoms but are
free to wander in the material
– Example: Metals such as copper and aluminum
• Insulators: Materials in which electrons are tightly
bound and belong to particular atoms and are not
free to wander about among other atoms in the
material, making them flow
– Example: Rubber, glass
© 2010 Pearson Education, Inc.
Conductors and Insulators
CHECK YOUR NEIGHBOR
When you buy a water pipe in a hardware store, the water
isn’t included. When you buy copper wire, electrons
A.
B.
C.
D.
must be supplied by you, just as water must be supplied for a
water pipe.
are already in the wire.
may fall out, which is why wires are insulated.
None of the above.
© 2010 Pearson Education, Inc.
Conductors and Insulators
CHECK YOUR ANSWER
When you buy a water pipe in a hardware store, the water
isn’t included. When you buy copper wire, electrons
A.
B.
C.
D.
must be supplied by you, just as water must be supplied for a
water pipe.
are already in the wire.
may fall out, which is why wires are insulated.
None of the above.
© 2010 Pearson Education, Inc.
Charging- Apply Electrical Charge by
CONTACT
• Charging by friction and contact.
Example:
Stroking cats fur, combing your hair, rubbing
your shoes on a carpet
• Electrons transfer from one material to
another by simply touching. For example,
– when a negatively charged rod is placed in
contact with a neutral object, some electrons will
move to the neutral object.
– http://www.bing.com/videos/search?q=van+de+graaf+generator&&view=deta
il&mid=B648FB2565AA7D565293B648FB2565AA7D565293&rvsmid=ABD0
6ACE3DE4C7CFF49CABD06ACE3DE4C7CFF49C&fsscr=0
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Charging- Apply Electrical Charge by
INDUCTION
Induction: Consider two insulated metal spheres A and B.
a. They touch each other, so in effect they form a single
uncharged conductor.
b. When a negatively charged rod is brought near A, electrons in
the metal, being free to move, are repelled as far as possible
until their mutual repulsion is big enough to balance the
influence of the rod. The charge is redistributed.
c. If A and B are separated while the rod is still present, each will
be equal and oppositely charged.
© 2010 Pearson Education, Inc.
Charging
• Charging by induction
– If you bring a charged object near a conducting
surface, electrons are made to move in the
surface material, even without physical contact.
– Example: The negative
charge at the bottom of
the cloud induces a
positive charge on the
buildings below.
© 2010 Pearson Education, Inc.
Open up your book and work on
the following problems
• Ranking page 400 1 and 2
• Exercises page 401 8, 11, 13, 15, 19, 22,
23, 25, 28, 29, 33, 34, 35
© 2010 Pearson Education, Inc.
Chapter 22
Chapter Objectives
• Electrical Forces and
Charges
• Conservation of Charge
• Coulomb’s Law
• Conductors and
Insulators
• Charge Polarization
• Electric Field
• Electric Potential
• Electric Energy Storage
© 2010 Pearson Education, Inc.
Warm-Up
• Get out HW
• We will check HW
• Review for Quiz
• Take the Quiz then have
a lecture
Electric Field
Electric field
• Space surrounding an electric charge (an
energetic aura)
• Describes electric force
• Around a charged particle obeys inverse-square
law
• Force per unit charge
E= F/q
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Electric Field
Electric field direction
• Same direction as the force on a positive charge
• Opposite direction to the force on an electroncloser = stronger
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Electric Field
Both Lori and the
spherical dome of the
Van de Graaff generator
are electrically charged.
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© 2010 Pearson Education, Inc.
© 2010 Pearson Education, Inc.
© 2010 Pearson Education, Inc.
Electric Potential
Electric potential (voltage)
• Energy per charge possessed by a charged
particle due to its location
• May be called voltage—potential energy per
charge
• In equation form:
Electric potential  electric potential energy
amount of charge
© 2010 Pearson Education, Inc.
Electric Potential
Electric potential (voltage) (continued)
• Unit of measurement: volt, 1 volt  1 joule
1 coulomb
Example:
• Twice the charge in same location has twice the
electric potential energy but the same electric
potential.
• 3 times the charge in same location has 3 times the
electric potential energy but the same electric
potential (2 E/2 q = 3 E/3 q = V)
© 2010 Pearson Education, Inc.
Electric Potential
CHECK YOUR NEIGHBOR
Electric potential energy is measured in joules. Electric
potential, on the other hand (electric potential energy per
charge), is measured
A.
B.
C.
D.
in volts.
in watts.
in amperes.
also in joules.
© 2010 Pearson Education, Inc.
Electric Potential
CHECK YOUR ANSWER
Electric potential energy is measured in joules. Electric
potential, on the other hand (electric potential energy per
charge), is measured
A.
B.
C.
D.
in volts.
in watts.
in amperes.
also in joules.
© 2010 Pearson Education, Inc.
Chapter 22
Chapter Objectives
• Electrical Forces and
Charges
• Conservation of Charge
• Coulomb’s Law
• Conductors and
Insulators
• Charge Polarization
• Electric Field
• Electric Potential
• Electric Energy Storage
© 2010 Pearson Education, Inc.
Warm-Up
• Finish lecture if needed
• Practice
Practice= CW NOT HW
1. Rev questions page 400 27 and 28
2. Exercises page 402 50-54 and 60 ( on
pg 403)
3. Problems page 403 8 and 9
4. You and a partner will create 2 quiz
questions. One conceptual question
about the electric field and one math
question about electric potential. We may
use these on the next quiz so write good
ones!
© 2010 Pearson Education, Inc.
Chapter 23
Objective
• Flow of Charge
• Electric Current
• Voltage Sources
• Electrical Resistance
• Ohm’s Law
• Direct Current and
Alternating Current
© 2010 Pearson Education, Inc.
Warm-Up- Look in your
book
1. What type of device
uses DC?
2. What type of device
uses AC?
3. What type of current are
the electric field lines
around the earth?
Edison vs. Tesla- DC vs. AC current
1.
2.
3.
4.
5.
Who was Thomas Edison and what is he given credit for invent?
Where did Edison have a summer home?
Did he REALLY invent this?
Who was Nikola Tesla and what many things did he invent? There are a few
What does DC and AC stand for?
http://www.pbs.org/wgbh/amex/edison/sfeature/acdc.html
6. Which type of current did Edison approve and what type of current did Tesla
approve?
7. Was Tesla ever rich?
8. Did Tesla dress well?
9. Did the ladies like Tesla?
10. Did he like them back….??
11. Why did cats and dogs start to disappear while Edison was “studying” AC current?
Rap:
http://blog.press.princeton.edu/2013/04/04/tesla-vs-edison-epic-rap-battle/
Elephant:
http://www.bing.com/videos/search?q=edison+and+elephant+ac+current&view=detail&
mid=8D30135B038BA48C76668D30135B038BA48C7666&first=0&FORM=NVPFVR...
Comic:
http://theoatmeal.com/comics/tesla
Movie:
https://www.youtube.com/watch?v=RB882PSnnJY
© 2010 Pearson Education, Inc.
Chapter 23
Chapter Objectives
• Flow of Charge
• Electric Current
• Voltage Sources
• Electrical Resistance
• Ohm’s Law
• Direct Current and
Alternating Current
© 2010 Pearson Education, Inc.
Warm-Up
• Review for Quiz
• Take the Quiz
• Complete WU then
Lecture
Electric Current
Which of these statements is true?
A.
B.
C.
D.
Electric current is a flow of electric charge.
Electric current is stored in batteries.
Both A and B are true.
Neither A nor B are true.
© 2010 Pearson Education, Inc.
Electric Current
Which of these statements is true?
A.
B.
C.
D.
Electric current is a flow of electric charge.
Electric current is stored in batteries.
Both A and B are true.
Neither A nor B are true.
Explanation:
Voltage, not current, is stored in batteries. The voltage will
produce a current in a connecting circuit. The battery moves
electrons already in the wire, but not necessarily those in the
battery.
© 2010 Pearson Education, Inc.
Flow of Charge
• When the ends of an electrical conductor are at
different electric potentials—when there is a
potential difference—charge flows from one end
to the other.
– Analogous to water flowing from higher pressure to
lower pressure
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Flow of Charge
• To attain a sustained flow of charge in a conductor,
some arrangement must be provided to maintain a
difference in potential while charge flows from one
end to the other.
– A continuous flow is possible if the difference in water
levels—hence the difference in water pressures—is
maintained with the use of a pump.
© 2010 Pearson Education, Inc.
Electric Current
Electric current
• Flow of charged particles
– In metal wires
• Conduction electrons are charge carriers that are free to
move throughout atomic lattice.
• Protons are bound within the nuclei of atoms.
– In fluids
• Positive ions and electrons constitute electric charge flow.
© 2010 Pearson Education, Inc.
Ohm’s Law
Ohm’s law
• Relationship between voltage, current, and
resistance
• States that the current in a circuit varies in direct
proportion to the potential difference, or voltage,
and inversely with the resistance
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Ohm’s Law
Ohm’s law (continued)
• In equation form: Current  voltage
resistance
Example:
• For a constant resistance, current will be twice as
much for twice the voltage.
• For twice the resistance and twice the voltage, current
will be unchanged.
Resistors
• Circuit elements that regulate current inside
electrical devices.
© 2010 Pearson Education, Inc.
Ohm’s Law
Electric shock
• Damaging effects of shock result from current
passing through the body.
• Electric potential difference between one part of
your body and another part depends on body
condition and resistance, which can range from
100 ohms to 500,000 ohms.
© 2010 Pearson Education, Inc.
Ohm’s Law
CHECK YOUR NEIGHBOR
When you double the voltage in a simple electric circuit,
you double the
A.
B.
C.
D.
current.
resistance.
Both A and B.
Neither A nor B.
© 2010 Pearson Education, Inc.
Ohm’s Law
CHECK YOUR ANSWER
When you double the voltage in a simple electric circuit,
you double the
A.
B.
C.
D.
current.
resistance.
Both A and B.
Neither A nor B.
Explanation:
This is a straightforward application of Ohm’s law.
Current 
© 2010 Pearson Education, Inc.
voltage
resistance
Electric Circuits- R, I and V
Circuits
• Connected in two common ways:
– series
• forms a single pathway for electron flow between
the terminals of the battery, generator, or wall
outlet
– parallel
• forms branches, each of which is a separate path
for the flow of electrons
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Electric Circuits- R=sum and
I=same
V=sum
Series circuits
• Characteristics of series circuit
1. Electric current through a single pathway.
2. Total resistance to current is the sum of individual
resistances.
3. Current is equal to the voltage supplied by the source
divided by the total resistance of the circuit. I=V/R
© 2010 Pearson Education, Inc.
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Electric Circuits
Series circuits
• Characteristics of series circuit (continued):
4. The total voltage impressed across a series circuit
divides among the individual electrical devices in the
circuit so that the sum of the “voltage drops” across the
resistance of each individual device is equal to the total
voltage supplied by the source.
5. The voltage drop across each device are proportional
to its resistance.
6. If one device fails, current in the entire circuit ceases.
© 2010 Pearson Education, Inc.
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Electric Circuits- R= “sum”
I=sum V=same
Parallel circuits
• Characteristics of parallel circuit:
1. Voltage is the same across each device.
2. The total current in the circuit divides among the
parallel branches. The amount of current in each branch
is inversely proportional to the resistance of the branch.
3. The total current in the circuit equals the sum of the
currents in its parallel branches.
© 2010 Pearson Education, Inc.
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Electric Circuits
Parallel circuits
• Characteristics of parallel circuit (continued):
4. As the number of parallel branches is increased, the
overall resistance of the circuit is decreased.
5. A break in one path does not interrupt the flow of
charge in the other paths.
© 2010 Pearson Education, Inc.
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Electric Circuits
CHECK YOUR NEIGHBOR
When two identical lamps in a circuit are connected in
parallel, the total resistance is
A.
B.
C.
D.
less than the resistance of either lamp.
the same as the resistance of each lamp.
less than the resistance of each lamp.
None of the above.
© 2010 Pearson Education, Inc.
Electric Circuits
CHECK YOUR ANSWER
When two identical lamps in a circuit are connected in
parallel, the total resistance is
A.
B.
C.
D.
less than the resistance of either lamp.
the same as the resistance of each lamp.
less than the resistance of each lamp.
None of the above.
Explanation:
Resistors in parallel are like extra lines at a checkout counter.
More lines means less resistance, allowing for more flow.
© 2010 Pearson Education, Inc.
Electric Circuits
CHECK YOUR NEIGHBOR
Consider a lamp powered by a battery. Charge flows
A.
B.
C.
D.
out of the battery and into the lamp.
from the negative terminal to the positive terminal.
with a slight time delay after closing the switch.
through both the battery and the lamp.
© 2010 Pearson Education, Inc.
Electric Circuits
CHECK YOUR ANSWER
Consider a lamp powered by a battery. Charge flows
A.
B.
C.
D.
out of the battery and into the lamp.
from the negative terminal to the positive terminal.
with a slight time delay after closing the switch.
through both the battery and the lamp.
Explanation:
Remember, charge is already in all parts of the conducting circuit.
The battery simply gets the charges moving. As much charge
flows in the battery as outside. Therefore, charge flows through
the entire circuit.
© 2010 Pearson Education, Inc.
Ch 23 Practice
• Plug and Chug page 420 ALL (1-6)
• Ranking page 420 1, 2, 3
• Exercises page 421 1, 2, 3, 8, 9, 26, 30,
31, 32, 33
© 2010 Pearson Education, Inc.
Chapter 24
Objectives
• Magnetic Forces, Poles,
Fields
• Magnetic Domains
• Electric Currents and
Magnetic Fields
• Electromagnets
• Magnetic Force on
Moving Charged Particles
• Magnetic Force on
Current Carrying Wires
• Earth’s Magnetic Field
© 2010 Pearson Education, Inc.
Warm-Up
• Get out HW
• Magnetism is a Force,
can you name any
others?
Forces
gravitational
Electric- coulomb’s
law- just charged
particles
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Magneticmotion of
charged
particles
Magnetic Poles
CHECK YOUR NEIGHBOR
A weak and strong magnet repel each other. The
greater repelling force is by the
A.
B.
C.
D.
stronger magnet.
weaker magnet.
Both the same.
None of the above.
© 2010 Pearson Education, Inc.
Magnetic Poles
CHECK YOUR ANSWER
A weak and strong magnet repel each other. The
greater repelling force is by the
A.
B.
C.
D.
stronger magnet.
weaker magnet.
Both the same.
None of the above.
Explanation:
Remember Newton’s third law!
© 2010 Pearson Education, Inc.
Magnetic Fields
Magnetic fields
• Strength indicated by
closeness of the lines
– lines close together; strong
magnetic field
– lines farther apart; weak
magnetic field
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Magnetic Fields
Magnetic fields (continued)
• Produced by two kinds of electron motion
– electron spin
• main contributor to magnetism
• pair of electrons spinning in same direction creates a stronger
magnet
• pair of electrons spinning in opposite
direction cancels magnetic field of the
other
– electron revolution
© 2010 Pearson Education, Inc.
http://video.nationalgeographic.com/video/news
/norway-aurora-borealis-vin
© 2010 Pearson Education, Inc.
Magnetic Fields
CHECK YOUR NEIGHBOR
The source of all magnetism is
A.
B.
C.
D.
electrons rotating around an atomic nucleus.
electrons spinning around internal axes.
either or both A and B.
tiny bits of iron.
© 2010 Pearson Education, Inc.
Magnetic Fields
CHECK YOUR ANSWER
The source of all magnetism is
A.
B.
C.
D.
electrons rotating around an atomic nucleus.
electrons spinning around internal axes.
either or both A and B.
tiny bits of iron.
© 2010 Pearson Education, Inc.
Magnetic Fields
CHECK YOUR NEIGHBOR
Where magnetic field lines are more dense, the field there
is
A.
B.
C.
D.
weaker.
stronger.
Both A and B.
Neither A nor B.
© 2010 Pearson Education, Inc.
Magnetic Fields
CHECK YOUR ANSWER
Where magnetic field lines are more dense, the field there
is
A.
B.
C.
D.
weaker.
stronger.
Both A and B.
Neither A nor B.
© 2010 Pearson Education, Inc.
Chapter 24
Objectives
• Magnetic Forces, Poles,
Fields
• Magnetic Domains
• Electric Currents and
Magnetic Fields
• Electromagnets
• Magnetic Force on
Moving Charged Particles
• Magnetic Force on
Current Carrying Wires
• Earth’s Magnetic Field
© 2010 Pearson Education, Inc.
Warm-Up
• 1. review
• 2. quiz
• 3. lecture
• 4. HW
Magnetic Domains
Magnetic domains
• Magnetized clusters of aligned
magnetic atoms
Permanent magnets made by
• placing pieces of iron or similar magnetic
materials in a strong magnetic field.
• stroking material with a magnet to align the
domains.
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Magnetic Domains
Difference between permanent magnet and
temporary magnet
• Permanent magnet
– alignment of domains remains once external magnetic field is
removed
• Temporary magnet
– alignment of domains returns to random arrangement once
external magnetic field is removed
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Magnetic Domains
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Electric Currents and Magnetic
Fields
Connection between electricity and
magnetism
• Magnetic field forms a pattern of concentric circles
around a current-carrying wire.
• When current reverses direction,
the direction of the field lines
reverse.
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Electric Currents and Magnetic
Fields
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Electric Currents and Magnetic
Fields
Magnetic field intensity
• increases as the number of loops increase in a
current-carrying coil temporary magnet.
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Electric Currents and Magnetic
Fields
Electromagnet
• Iron bar placed in a current-carrying coil
• Most powerful—employs superconducting coils that
eliminate the core
• Applications
– control charged-particle beams in high-energy accelerators
– lift automobiles and other
iron objects
– levitate and propel
high-speed trains
© 2010 Pearson Education, Inc.
Electric Currents and Magnetic Fields
CHECK YOUR NEIGHBOR
An electromagnet can be made stronger by
A.
B.
C.
D.
increasing the number of turns of wire.
increasing the current in the coil.
Both A and B.
None of the above.
© 2010 Pearson Education, Inc.
Electric Currents and Magnetic Fields
CHECK YOUR ANSWER
An electromagnet can be made stronger by
A.
B.
C.
D.
increasing the number of turns of wire.
increasing the current in the coil.
Both A and B.
None of the above.
HW: page 438
© 2010 Pearson Education, Inc.
1, 2, 4, 9, 13, 24
Chapter 25
Objective
• Electromagnetic Induction
• Faraday’s Law
• Generators and
Alternating Current
• Power Production
• Power Transmission
© 2010 Pearson Education, Inc.
Warm-Up
• Get out HW
• We need to check it
Electromagnetic Induction
Electromagnetic induction
• Discovered by Faraday and Henry
• Induces voltage by changing the magnetic field
strength in a coil of wire
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Electromagnetic Induction
Electromagnetic induction (continued)
• Induced voltage can be increased by
– increasing the number of loops of wire in a coil.
– increasing the speed of the magnet entering and
leaving the coil.
• Slow motion produces hardly any voltage.
• Rapid motion produces greater voltage.
© 2010 Pearson Education, Inc.
Electromagnetic Induction
Voltage is induced in the wire loop whether
the magnetic field moves past the wire or the
wire moves through the magnetic field.
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Electromagnetic Induction
When a magnet is plunged into a coil with twice as many
loops as another, twice as much voltage is induced. If the
magnet is plunged into a coil with 3 times as many loops,
3 times as much voltage is induced.
© 2010 Pearson Education, Inc.
Faraday’s Law
Faraday’s law
• States that the induced voltage in a coil is
proportional to the number of loops, multiplied
by the rate at which the magnetic field changes
within those loops.
• Amount of current produced by electromagnetic
induction is dependent on
– resistance of the coil,
– circuit that it connects,
– induced voltage.
© 2010 Pearson Education, Inc.
Faraday’s Law
It is more
difficult to push
the magnet into
a coil with
many loops
because the
magnetic field
of each current
loop resists the
motion of the
magnet.
© 2010 Pearson Education, Inc.
Faraday’s Law
CHECK YOUR NEIGHBOR
The resistance you feel when pushing a piece of iron into a
coil involves
A.
B.
C.
D.
repulsion by the magnetic field you produce.
energy transfer between the iron and coil.
Newton’s third law.
resistance to domain alignment in the iron.
© 2010 Pearson Education, Inc.
Faraday’s Law
CHECK YOUR ANSWER
The resistance you feel when pushing a piece of iron into a
coil involves
A.
B.
C.
D.
repulsion by the magnetic field you produce.
energy transfer between the iron and coil.
Newton’s third law.
resistance to domain alignment in the iron.
© 2010 Pearson Education, Inc.
Faraday’s Law
CHECK YOUR NEIGHBOR
More voltage is induced when a magnet is thrust into a coil
A.
B.
C.
D.
more quickly.
more slowly.
Both A and B.
Neither A nor B.
© 2010 Pearson Education, Inc.
Faraday’s Law
CHECK YOUR ANSWER
More voltage is induced when a magnet is thrust into a coil
A.
B.
C.
D.
more quickly.
more slowly.
Both A and B.
Neither A nor B.
© 2010 Pearson Education, Inc.
Faraday’s Law
CHECK YOUR NEIGHBOR
Not only is voltage induced when a magnet is thrust into a
coil of wire but ___________ is also induced.
A.
B.
C.
D.
current
energy
power
None of the above.
© 2010 Pearson Education, Inc.
Faraday’s Law
CHECK YOUR ANSWER
Not only is voltage induced when a magnet is thrust into a
coil of wire but ___________ is also induced.
A.
B.
C.
D.
current
energy
power
None of the above.
Comment: Don’t say energy or power, which are
conservation-of-energy no-no’s! Energy can be
transferred but not created by induction.
© 2010 Pearson Education, Inc.
Generators and Alternating
Current
Generator
• Opposite of a motor
• Converts mechanical energy into electrical energy via
coil motion
• Produces alternating voltage and current
© 2010 Pearson Education, Inc.
Generators and Alternating
Current
The frequency of alternating voltage induced
in a loop is equal to the frequency of the
changing magnetic field within the loop.
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Power Production
Transformer
• Input coil of wire—the primary powered by ac voltage
source
• Output coil of wire—the secondary connected to an
external circuit
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Power Production
Transformer (continued)
• Both wound on a common iron core so that the magnetic
field of the primary passes through the secondary
• Uses an alternating current and voltage in one coil to
induce an alternating current and voltage in a second
coil
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Power Production
Transformers can be step-up or step-down
voltage.
• Step-up transformer
– produces a greater voltage in the secondary than
supplied by the primary
– secondary has more turns in coil than the primary
• Step-down transformer
– produces a smaller voltage in the secondary than
supplied by the primary
– secondary has less turns in coil than the primary
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Power Production
Transformer transfers energy from one coil
to another. (continued)
Example:
• voltage stepped up before leaving power station
• voltage stepped down for distribution near cities by
cables that feed power to the grid
• voltage stepped down again before
being supplied to businesses and
consumers through substations
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Power Transmission
• Almost all electric energy sold today is in the form of ac
because of the ease with which it can be transformed from
one voltage to another.
• Large currents in wires produce heat and energy losses, so
power is transmitted great distances at high voltages and low
currents.
• Power is generated at 25,000 V or less and is stepped up near
the power station to as much as 750,000 V for long-distance
transmission.
• It is then stepped down in stages at substations and
distribution points to voltages needed in industrial applications
(often 440 V or more) and for the home (240 and 120 V).
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Power Production
CHECK YOUR NEIGHBOR
A step-up transformer in an electrical circuit can step up
A.
B.
C.
D.
voltage.
energy.
Both A and B.
Neither A nor B.
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Power Production
CHECK YOUR ANSWER
A step-up transformer in an electrical circuit can step up
A.
B.
C.
D.
voltage.
energy.
Both A and B.
Neither A nor B.
Explanation:
Stepping up energy is a conservation of energy no-no!
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