magnetism 9/10 turn in circuit lab from yesterday. 1.create a diagram of a two way switch. 2.take...
TRANSCRIPT
Magnetism
9/10
Turn in circuit lab from yesterday.
1.Create a diagram of a two way switch.2.Take the electromagnetic instruction sheet, circle the words you don’t understand. Underline main idea of each step.
• Magnetic field – area where magnetic force acts.
9/11
1. What comes to mind when you see this picture?2. What do you think causes this?
Scan the text • Do auroras occur only on Earth?
• Because auroras are caused by the interactions of solar winds and solar flares with the magnetic fields of a planet, you'd think they'd happen on other planets as well. What you need is:
• Solar flares and winds that provide the charged particles and energy to interact with a planet’s magnetic field
• A planetary magnetic field (probably of some strength) that traps electrons from space
• A planetary atmosphere that contains ionic gases that interact with energetic electrons from the magnetic field and produce light through excitation and relaxation of their electrons
So, with these conditions, we have observed auroras on So, with these conditions, we have observed auroras on Jupiter and and Saturn. Both planets have powerful magnetic fields and . Both planets have powerful magnetic fields and atmospheres with ionized gases, mainly hydrogen and helium. atmospheres with ionized gases, mainly hydrogen and helium. The The Hubble Space Telescope caught images of auroras on caught images of auroras on Jupiter, and the Cassini probe orbiting Saturn has photographed Jupiter, and the Cassini probe orbiting Saturn has photographed auroras there. auroras there.
What is Magnetism?
• Magnetism is the attraction of a magnet to another object.
Iron filings sprinkled on a sheet of paper over a bar Iron filings sprinkled on a sheet of paper over a bar magnet will tend to trace out a pattern of lines that magnet will tend to trace out a pattern of lines that surround the magnet. surround the magnet.
magnetic fieldmagnetic field -The space around a magnet, in which -The space around a magnet, in which a magnetic force is exerteda magnetic force is exerted
The shape of the field is revealed by The shape of the field is revealed by magnetic field magnetic field lines.lines.
36.2 Magnetic Fields
What are Magnetic Poles?
• Magnets have two ends, called magnetic poles.
• Magnetism is strongest at the poles of a magnet.
What are the magnetic properties of the Earth?
• The Earth has an immense magnetic field around it called the magnetosphere.
The deflection of charged The deflection of charged particles by magnetic fields particles by magnetic fields provides a TV picture. provides a TV picture.
Charged particles from outer Charged particles from outer space are deflected by space are deflected by EarthEarth’’s magnetic field, which s magnetic field, which reduces the intensity of reduces the intensity of cosmic radiation. cosmic radiation.
A much greater reduction in A much greater reduction in intensity results from the intensity results from the absorption of cosmic rays in absorption of cosmic rays in the atmosphere.the atmosphere.
36.6 Magnetic Forces on Moving Charged Particles
Magnetic Poles
• Magnetic poles that are alike repel each other.
• North repels North• South repels South
• Poles that are not alike attract each other
• North attracts South• South attracts North
What is a Magnetic Field?
• The magnetic force exerted in the region around the magnet is the magnetic field.
• This allows magnets to interact without touching.
What are Magnetic Field Lines?
• Magnetic Field Lines spread out from one pole, curve around the magnet, and return to the other pole.
What do atoms have to do with it?
• All atoms have magnetic fields because of the charged particles inside.
• Most atoms’ magnetic fields point in random directions, so they all cancel each other out.
Spin MagnetismEvery spinning electron is a tiny magnet.Every spinning electron is a tiny magnet.
• A pair of electrons spinning in the same A pair of electrons spinning in the same direction makes up a stronger magnet. direction makes up a stronger magnet.
• Electrons spinning in opposite directions Electrons spinning in opposite directions work against one another. work against one another.
• Their magnetic fields cancel. Their magnetic fields cancel.
36.3 The Nature of a Magnetic Field
Magnetic Fields
Magnetic fields• 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 theother
– electron revolution
Most substances are not magnets because the Most substances are not magnets because the various fields cancel one another due to various fields cancel one another due to electrons spinning in opposite directions. electrons spinning in opposite directions.
In materials such as iron, nickel, and cobalt, In materials such as iron, nickel, and cobalt, however, the fields do not cancel one another however, the fields do not cancel one another entirely. entirely.
An iron atom has four electrons whose spin An iron atom has four electrons whose spin magnetism is not canceled. magnetism is not canceled.
Each iron atom, then, is a tiny magnet. The same Each iron atom, then, is a tiny magnet. The same is true to a lesser degree for the atoms of nickel is true to a lesser degree for the atoms of nickel and cobalt.and cobalt.
36.3 The Nature of a Magnetic Field
What do atoms have to do with it?
• In magnetized material, all or most of the magnetic fields are arranged in the same direction.
• A material that keeps its magnetism is called a permanent magnet.
The magnetic fields of individual iron atoms are The magnetic fields of individual iron atoms are strong.strong.
• Interactions among adjacent iron atoms Interactions among adjacent iron atoms cause large clusters of them to line up with cause large clusters of them to line up with one another. one another.
•magnetic domainsmagnetic domains clusters of aligned atomsclusters of aligned atoms
• Each domain is perfectly magnetized, and is Each domain is perfectly magnetized, and is made up of billions of aligned atoms. made up of billions of aligned atoms.
• The domains are microscopic, and there are The domains are microscopic, and there are many of them in a crystal of iron.many of them in a crystal of iron.
36.4 Magnetic Domains
The arrows The arrows represent domains, represent domains, where the head is a where the head is a north pole and the north pole and the tail a south pole. tail a south pole. Poles of neighboring Poles of neighboring domains neutralize domains neutralize one anotherone another’’s s effects, except at effects, except at the ends.the ends.
36.4 Magnetic Domains
The compass aligns with the The compass aligns with the magnetic field of Earth, but the magnetic field of Earth, but the magnetic poles of Earth do not magnetic poles of Earth do not coincide with the geographic coincide with the geographic poles.poles.
The magnetic pole in the Northern The magnetic pole in the Northern Hemisphere, for example, is Hemisphere, for example, is located some 800 kilometers from located some 800 kilometers from the geographic North Pole.the geographic North Pole.
This means that compasses do This means that compasses do not generally point to true north.not generally point to true north.
The discrepancy is known as the The discrepancy is known as the magnetic declination.magnetic declination.
36.9 Earth’s Magnetic Field
Currents in the molten part of Earth Currents in the molten part of Earth beneath the crust provide a better beneath the crust provide a better explanation for Earthexplanation for Earth’’s magnetic field. s magnetic field.
Most geologists think that moving Most geologists think that moving charges looping around within Earth charges looping around within Earth create its magnetic field. Because of create its magnetic field. Because of EarthEarth’’s great size, the speed of charges s great size, the speed of charges would have to be less than one would have to be less than one millimeter per second to account for the millimeter per second to account for the field.field.
Another possible cause for EarthAnother possible cause for Earth’’s s magnetic field is convection currents magnetic field is convection currents from the rising heat of Earthfrom the rising heat of Earth’’s core. s core. Perhaps such convection currents Perhaps such convection currents combined with the rotational effects of combined with the rotational effects of Earth produce EarthEarth produce Earth’’s magnetic fields magnetic field. .
36.9 Earth’s Magnetic Field
More than 20 reversals have taken place in the past 5 More than 20 reversals have taken place in the past 5 million years. The most recent occurred 780,000 million years. The most recent occurred 780,000 years ago. years ago.
We cannot predict when the next reversal will occur We cannot predict when the next reversal will occur because the reversal sequence is not regular. because the reversal sequence is not regular.
Recent measurements show a decrease of over 5% of Recent measurements show a decrease of over 5% of EarthEarth’’s magnetic field strength in the last 100 years. If s magnetic field strength in the last 100 years. If this change is maintained, there may be another field this change is maintained, there may be another field reversal within 2000 years.reversal within 2000 years.
36.9 Earth’s Magnetic Field
S
N
1. What happens if you break a 1. What happens if you break a magnet in half? magnet in half?
2. Draw a picture of what it will 2. Draw a picture of what it will look like if you spread iron look like if you spread iron fillings on a bar magnet.fillings on a bar magnet.
36.1 Magnetic PolesIf you break a bar magnet in half, each half still behaves as a complete magnet. Break the pieces in half again, and you have four complete magnets.Even when your piece is one atom thick, there are two poles. This suggests that atoms themselves are magnets.
MRI
• Magnetic resonance imaging (MRI) is a test that uses a magnetic field and pulses of radio wave energy to make pictures of organs and structures inside the body
• Sucks metal out
Magnets make you feel better?• Q: What is Transcranial Magnetic Stimulation (TMS), and how does it help depression?• A: TMS activates certain parts of the brain by using electrical energy passed through a coil of
wires to create a powerful magnetic field. During the procedure, energy from this magnetic field is transferred into a patient's brain by means of the coil device applied to the head. Unlike direct electrical energy, energy from the magnetic field passes through skin and skull, activating the brain painlessly and without surgery or sedation. We apply TMS to the front area of the brain, an area associated with mood regulation. Not unlike many anti-depressant medications, TMS affects brain functions and chemical activity, effectively "jump -starting" mood regulation structures in the brain, resulting in dramatic improvements in depressed patients.
Accelerators
LHC
A superconductive disk on the bottom, cooled
by liquid nitrogen, causes the magnet
above to levitate. The floating magnet
induces a current, and therefore a magnetic
field, in the superconductor, and
the two magnetic fields repel to levitate the
magnet.
For more information on the CERN HST Programme http://teachers.web.cern.ch/teachers/
9/12
• What is the largest magnet in the world?
• How do these birds know where to go?
• “Is it true that the Earth‘s magnetic field is about to flip?• Like football teams at half time, geophysicists think that the Earth’s magnetic poles could
soon switch ends with the magnetic north pole becoming south, and the magnetic south pole becoming north. Fortunately, when they say ‘soon’ geophysicists are thinking in geological timescales and they actually mean sometime in the next few thousand years.
• It’s thought that the Earth’s magnetic field is generated by the molten iron core at the centre of the planet. The molten iron has currents of its own, just like an ocean, and these moving currents create the magnetic field. But the currents are not consistent and the Earth’s magnetic field moves around, with the magnetic north pole currently drifting by about 10 miles a year.”
• http://www.physics.org/facts/frog-magnetic-field.asp
Fun fact
• Dogs use the Earth’s magnetic field when they’re relieving themselves. Not only that, but canines choose to do so in a north-south axis, Says a new study published in the Frontiers in Zoology
Great questions from yesterday
• How do they make magnets?- stay tuned, Monday we will find out
• What would happen if we had no magnetosphere?
-Solar flares might knock out power grids and where plenty of sunblock and the northern lights would no longer be northern, they would be every where
• Doesn’t science cause war? • Science creates technology, it is what humans decide to do with it is what
creates war
Homework due mondayBackground: “What is a magnetic field? What is a magnet?” reading
Claim : How were you able to create a compass• Evidence : How were you able to tell it was a compass? (include drawings)• Reasoning : Explain how your compass worked. Your explanation should include magnetic domains, magnetosphere, south pole north pole, magnetic field. What future questions do you have?
9/15
• How does the compass show the magnetic field?
• What do electrons have to do with magnetism
• How was electricity discovered?
• Turn in reports
• Ancient battery near Bagdad
An Aurora Borealis Fun Fact
• Seeing the Northern Lights is not a good thing to some people. It is a traditional belief that when the northern lights are shinning in the night sky, it means that the spirits are dancing because the know that somebody is going to begin their journey to the spirit world/heaven.
Future questions
What do Electric Currentshave to do with Magnets?
• An electric current produces a magnetic field.
• The direction of the current determines the direction of the magnetic field.
Characteristics of Electromagnets
• Strength depends on the number of coils and the size of the iron core.
• The greater the number of turns the coil has the stronger the magnet will be.
• The closer the coils are the stronger the magnet will be.
Iron filings sprinkled on paper reveal the Iron filings sprinkled on paper reveal the magnetic field configurations about magnetic field configurations about
a.a.a current-carrying wirea current-carrying wire
b.b.a current-carrying loopa current-carrying loop
c.c.a coil of loopsa coil of loops
36.5 Electric Currents and Magnetic Fields
A superconducting electromagnet can generate a A superconducting electromagnet can generate a powerful magnetic field indefinitely without using powerful magnetic field indefinitely without using any power. any power.
Superconducting magnets can also be found in Superconducting magnets can also be found in magnetic resonance imaging (MRI) devices in magnetic resonance imaging (MRI) devices in hospitals.hospitals.
36.5 Electric Currents and Magnetic Fields
• At Fermilab near Chicago, superconducting electromagnets guide high-energy particles around the four-mile-circumference accelerator.
• http://www.pbs.org/wgbh/nova/physics/cern.html
What is an Electromagnet
• An Electromagnet -a strong magnet that can be turned on and off.
• It consists of a current-carrying wire wrapped around an iron core.
• Hans Christian Oersted found that a compass he was using reacted when a battery in his lab was switched on and off
How a speaker works
• All you need is an electromagnet, permanent magnet and a vibrating cone
• http://www.physics.org/article-questions.asp?id=54
• What else could you use electromagents for?
335 × 311 - education.com
9/16
• What are some modifications that can be done to increase the strength of the electromagnet?
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
Magnetic Forces Current-Carry Wires
Magnetic Force and Levitation
• When an upward magnetic force is greater than gravity, then an object can levitate.
• A magnetically levitated vehicle is shown in the figure to the right – a magplane.
• No friction, no vibrations
• http://www.ru.nl/hfml/research/levitation/diamagnetic/
• http://www.youtube.com/watch?v=tipublpl164 - understanding electricity – the science channel
In a simple DC motor, a permanent magnet produces a magnetic In a simple DC motor, a permanent magnet produces a magnetic field in a region where a rectangular loop of wire is mounted.field in a region where a rectangular loop of wire is mounted.
• The loop can turn about an axis. The loop can turn about an axis. • When a current passes through the loop, it flows in When a current passes through the loop, it flows in
opposite directions in the upper and lower sides of the loop. opposite directions in the upper and lower sides of the loop. • The loop is forced to move as if it were a galvanometer.The loop is forced to move as if it were a galvanometer.
36.8 Meters to Motors
Motors and Generators
• Electric Motor – a device that changes electric current into mechanical energy.
• Generator – a device that changes mechanical energy into electrical current.
Motor and GeneratorCHECK YOUR ANSWER
A motor and a generator are
A. similar devices.
B. very different devices with different applications.
C. forms of transformers.
D. energy sources.
Motor and GeneratorCHECK YOUR ANSWER
A motor and a generator are
A. similar devices.
B. very different devices with different applications.
C. forms of transformers.
D. energy sources.
Electromagnetic Induction
Electromagnetic induction – Moving a permanent magnet and a wire will induce a current
• discovered by Faraday and Henry• voltage is induced with change of magnetic field strength in a
coil of wire
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
Power Production
Using Faraday and Henry’s discovery of electromagnetic induction, Nikola Tesla and George Westinghouse showed that electricity could be generated in sufficient quantities to light cities.
How is electricity generated?• Demo: Magnet, wire, bulb
http://www.bbc.co.uk/bitesize/standard/physics/energy_matters/generation_of_electricity/revision/1/
How is electricity generated?
• Demo: Hand-crank electrical generator
• Demo: Faraday flashlight
http://www.secondchancegarage.com/public/91.cfm
9/17
• How many motors are in a car, list them.
• What are the three requirements for electric current to be produced?
• What is the difference between a motor and a generator?
9/18
• What is the picture about?• What are the 3 ways to increase the induced
current?• Is the system using AC or DC current, Why?• Tomorrow : Quiz and notebook check
• Electromagnetic wave – A wave of energy consisting of electric and magnetic fields
• Electromagnetic waves come from accelerating electric charges, often electrons in atoms. The energy given off travels in a wave that is partly electric and partly magnetic
Voltage generated = speed * number of turns * strength of fieldarea / time
where, as indicated in the figure:
Σ is a surface bounded by the closed contour ∂Σ,E is the electric field, B is the magnetic field.dℓ is an infinitesimal vector element of the contour ∂Σ,dA is an infinitesimal vector element f surface Σ. If its direction is orthogonal to that surface patch, the magnitude is the area of an infinitesimal patch of surface.
• Does a compass line up perpendicular or parallel to magnetic field lines?
• Does a compass line up perpendicular or parallel to magnetic field lines?
• The compass points parallel to the magnetic field.
• Does a compass line up perpendicular or parallel to magnetic field lines?
• The compass points parallel to the magnetic field.
• Why are the Aurora’s only located near the poles?
Moving electrons will interact with•A. an electric field•B. a magnetic field•C. Both a and B•D. none of the above
Moving electrons will interact with•A. an electric field•B. a magnetic field•C. Both a and B•D. none of the above
• On a half sheet of paper describe how electricity is generated?
• Underline the content vocabulary:
• Why is this important to know?
9/19
• What do you think is the source of most commercial generators?
• If an object sticks to a magnet, is the object a temporary magnet or a permanent magnet?
• Are you ready for the quiz• Notebook check - # of dates from 9/8
Hints
• # What moves most generators?• #12 cosmic rays are solar flares (think of
Northern lights)
9/22
• What is the most common type of generator used in the United states? The World?
• What comes to your mind when you hear the word energy?
• How do we get energy?
Energy sources
http://commons. wikimedia.org/wiki/File:2011_US_electricity_generation_by_source.png
How is electricity generated?• Demo: Magnet, wire, bulb
http://www.bbc.co.uk/bitesize/standard/physics/energy_matters/generation_of_electricity/revision/1/
How is electricity generated?
• A steady supply of heat to turn water to steam can be provided by:– Burning stuff (coal, natural gas, wood, etc.)– Controlled nuclear reactions– The sun– The Earth’s heat
• Or, turbines can be directly turned using:– Flowing water– Wind
• What resources should we use to obtain the energy to power our homes, schools and businesses?
• Wind, coal, oil, natural gas, nuclear power, solar, geothermal, something else?
• Turbine – part of a generator that has a part with blades that are caused to spin by pressure from water, steam, or air
Small group discussion
• Go to http://www.iea.org/statistics/statisticssearch/ and find at least one country that generates its electricity with a very different balance of sources than the U.S.
• .
Energy Sources
http://www.iea.org/statistics/statisticssearch/
Why does Norway lead the world in hydroelectricity?
The environment dictates the energy source.
9/24
• What is the main idea behind your presentation?
• What future questions are you going to research today?
• - find two sources• Optional – print 1 or 2 pictures
9/25
• On a scale of 1-5 how confident do you feel about explaining the content of your poster.
• What are some key vocabulary words in your poster?
• What more do you need to do?
• How can I help?
• Samples of peer assessment
9/26
• What is the most interesting thing you have learned from your research?
• What are characteristics of a good presentation?
• 10 minutes – polish presentation• 30 minutes – gallery walk • 10 minutes – reflection
• Grade yourself out of 10 points (see rubric)• What percentage of the work did each group member
do?
• On a separate sheet of paper create a reflection on your poster.
• What did you think you did well? • What do you think might make your poster stronger? Did you enjoy the gallery
walk? How would you compare this way of learning to other ways of learning? • Discuss what you thought of your classmate’s presentations. Write down three
of the most interesting things you learned? • Give a brief summary of your poster
PSTL 1163: Physics by InquiryEnvironmental connections
Unit 1: Environmental impacts of electricity generation
Day 3: Environmental impacts
Key questions• What are the environmental impacts of
different sources of energy for generating electricity?
• What are the other impacts of the generation and distribution of electricity?
Fossil fuels• Drilling/mining for fossil fuels disturbs the
environment• Resulting pollutants (besides CO2)
– Gases: CO, SO2, NOx: Cause acid rain, ground level ozone, fine particulates --> respiratory problems
– Solids: Coal ash, containing mercury, lead, cadmium, arsenic, etc.: Cause neurological damage and heart disease
• 130 million tons annually, enough to fill the Grand Canyon• Coal ash disposal is regulated by the states, rather than the
federal government (What are the implications?)• People living closest to power plants, who have the largest
exposure to coal ash toxins are typically rural, poor, and minority populations (now defined as special populations)
Coal ash
http://clclt.com/theclog/archives/2010/08/03/dems-may-have-lost-their-minds-over-coal-ash-regulation
http://appvoices.org/2013/10/08/court-to-epa-get-moving-on-coal-ash/
Nuclear• Reactor breaches due to technical problems
(Chernobyl, 1986), natural disasters (Fukushima, 2011)
• Disposal of nuclear waste• Common misconception: Which is more
dangerous? Waste that is highly radioactive, or not-so highly radioactive?
• There is currently no central repository for storage of nuclear waste in the U.S.– Discussion: Pros and cons of a central storage
facility
Renewable energy sources
• Hydropower– Ecosystem changes (water temperature, chemistry,
flow rate)– China’s Three Gorges Dam (2012): Flooded
archaeological sites, displaced 1.3 M people, increased risk of landslides
• Wind and solar– Land must be cleared– Wind turbines and solar towers have a visual impact
on landscape and kill birds– Some materials such as lubricating oils (wind) and
heat transfer fluids (solar) are toxic.
Electricity distribution• Power lines impact visual landscape and require modifications
to the environment (keeping trees pruned back).• Underground power lines are more expensive and may have
no less impact.
www.nesec.org theboweryboys.blogspot.com
9/29
• Complete the table
• Last week we looked at different ways electricity can be generated. What do you think happens after electricity is generated?
Pro con
Wind
solar
Fossil fuel
Hydroelectricity
Nuclear
Electric Grid uses Transformers
• Voltage generated in power stations is stepped up with transformers prior to being transferred across the country by overhead cables.
• Then other transformers reduce the voltage before supplying it to homes, offices, and factories.
• Last week we looked at different ways electricity can be generated. What do you think happens after electricity is generated?
The Transformer—Boosting or Lowering Voltage
• input coil of wire —primary powered by AC voltage source• output coil of wire —secondary connected to external circuit
The Transformer
Transformer (continued)• both wound on a common iron core • then magnetic field of primary passes through secondary• uses ac in one coil to induce ac in second coil
The Transformer
• Transformer relationship:
• Vp / NP = Vs / Ns
primary voltagenumber of primary turns
= secondary voltagenumber of secondary turns
Transformers Everywhere
• This common transformer lowers 120V to 6V or 9V. It also converts AC to DC by means of a diode inside.
• A common neighborhood transformer that typically steps 2400V down to 240V.
Electric Grid uses Transformers
• Voltage generated in power stations is stepped up with transformers prior to being transferred across the country by overhead cables.
• Then other transformers reduce the voltage before supplying it to homes, offices, and factories.
Transformer Power
• Neglecting heat losses, power into a transformer = power out of transformer.
secondaryprimary current x Voltagecurrent x Voltage
Electric Power
• Electric power is equal to the product of the voltage and current.
• P=I * V
Electric Power Voltage current
• Fill out known measurements• Find equations where there is only one
variable missing• Solve for unknowns
• Number of coils = number of turns• VAC = volts• I kw = 1000 watt
9/30
• A primary coil has 100 turns and has a voltage of 120 volts, how many volts would go through the secondary coil if it has 10 turns?
• How well do you understand your transformers worksheet?
• Use the formula sheet to create a definition of electric potential.
Benchmark assessment friday
• (I) Electric current – a flow of electrons, measured in amperes (amps).
• (V) Electric potential – potential difference per charge. Measured in volts
• (R) – resistance – - ability to resist the flow of electrons, measured in ohms
10/1
1. Think about V=I*R, what happens to the resistance as the current goes up?
2. What happened to the current of the circuit as more bulbs are added in series, in parallel?
3. What happens to the resistance of the circuit as more bulbs are added in series? In parallel?
Total resistance of resistors in series : R = R1 + R2 + R3 +
A series circuit is shown in the diagram above. The total resistance is the sum of the individual resisters.
The current flows through each resistor in turn. If the values of the three resistors are 10, 20 and 30, what is the total resistance?
Key idea: What happens to the total current of the circuit as more resisters are added in series?
A series circuit is shown in the diagram above. The total resistance is the sum of the individual resisters.
Key idea: What happens to the total current of the circuit as more resisters are added in series?
In a series circuit – as more resisters are added the current goes down and the resistance goes up
With a 10 V battery and the total resistance is 20.
by V = I R the total current in the circuit is:
I = V / R = 10 / 20 = 0.5 A.
The current through each resistor would be 0.5 A
Parallel circuits
• The total resistance of a set of resistors in parallel is found by adding up the reciprocals of the resistance values, and then taking the reciprocal of the total:
• equivalent resistance of resistors in parallel:
• 1 / R = 1 / R1 + 1 / R2 + 1 / R3 +...
What happens to the current of the parallel circuit as more resisters are added?
Parallel circuits• The total resistance of a set of resistors in parallel is found by
adding up the reciprocals of the resistance values, and then taking the reciprocal of the total:
• equivalent resistance of resistors in parallel:What happens to the current of the parallel circuit as more resisters are added?
As more resisters are added in parallel the current across the battery increases and the resistance decreases, think about the splits.
Series parallel analogy
• Usually when I drive down the road I notice the more cars that are on the road, the slower traffic goes. Create an analogy to explain current, resistance, series and parallel based on this analogy.
• Does this analogy break down at any point?
• Voltage drops – voltage is going to be the same as the source across each branch of the parallel.
• In series – the voltage is shared in each of the bulbs.
• If the battery voltage is 6, in series the voltage drop is 2v each, in parallel the voltage drop is 6 v each
• The current above has a 10 volt power source. The value of the resisters are
r1= 1, r2= 5, r3= 101. What is the current across each resister?2. What is the total current?3. What is the complete resistance?4. What is the power going through the battery?
Exit slip
Using V= I *R
With a 10 V battery, by V = I R the total current in the circuit is: I = V / R = 10 / 2 = 5 A.The individual currents can also be found using I = V / R. The voltage across each resistor is 10 V, so:I1 = 10 / 8 = 1.25 A I2 = 10 / 8 = 1.25 A I3=10 / 4 = 2.5 A
The equivalent resistance for a pair of equal resistors in parallel is half the value of either resistor.The equivalent resistance for a pair of 1-ohm resistors in parallel is 0.5 ohm. The equivalent resistance is less because the current has “twice the path width” when it takes the parallel path.
35.6 Combining Resistors in a Compound Circuit
a. The equivalent resistance of two 8-ohm resistors in series is 16 ohms.
35.6 Combining Resistors in a Compound Circuit
a. The equivalent resistance of two 8-ohm resistors in series is 16 ohms.
b. The equivalent resistance of two 8-ohm resistors in parallel is 4 ohms.
35.6 Combining Resistors in a Compound Circuit
What causes lightning?
• http://www.youtube.com/watch?v=RLWIBrweSU8
• What comes to mind when you think of lightning?
• Are you safe in a car during a lightning storm?
• How is electric potential related to an electric current?
bulbs
• Why doesn’t a 1.5 volt battery power your car?
• Why doesn’t a 1.5 volt battery power a 6 volt computer motor?
• a 12 volt motor V=6, v=1.5 say the resistance is 1 ohm. Lets solve for current for each battery. I = v/r. The current for the 6 volt would be 6/1= 6 amp. The current for the 1.5 would be 1.5/1 = 1.5. one.
• What are three things needed to generate electricity?