Bellringer What are some ways that you use
Bellringer �What are some ways that you use electricity in your daily life?
Objectives �We will investigate electricity as you are used to seeing it, and using it at home �Learn what electric current is and what an electric circuit it
Electrostatics Test �I will have your grades by the end of the day. �Does 100=99. 999999 forever?
Does 100=99. 99999999? �
Updates �The Dance! �Science �Test Learning Center average 6 points behind last year… �Midterm Corrections �Physics Club
Electric Current and Circuits
Electricity as you know it! �Electric Current is a flow of charged particles. �Conventional Current is the direction in which a positive test charge moves. • The flow of electrons and conventional current are in opposite directions
Electric Current �Electric Current is measured in Amperes (A, or amps) � 1 Ampere is equal to 1 Coulomb moved past a single point in 1 second
Electric Current �Electric current is the measure of electrons moving past a certain point. • Much like the current of a river is measure by the amount of water moving past a certain point.
Electric Current �
Amps � 0. 001 -0. 01 Amps = Little to no shock � 0. 01 -0. 02 Amps = Painful shock � 0. 02 -0. 075 Amps= Serious shock, muscle control lost � 0. 075 -0. 1 Amps = Heart misses beats � 0. 1 -0. 2 Amps= Changes heart’s rhythm, possible death
Amps �Over 0. 2 Amps = Severe burns and muscle contraction. Heart stops from chest muscle pressure. Internal organs are damaged. Can survive if you are removed from the circuit fast enough. Very painful recovery, but heart very likely to go back to its regular beat
Amps �If a wire has 1 amp of current running through it should you touch it? �http: //www. youtube. com/watch? v=um. Dr 0 m Puy. Qc
Examples �
Practice �What is the current of a 6 C charge that moves past a point in 2. 5 seconds? �I=2. 4 Amperes �How long does it take a 5 amp current to move 3 Coulombs of charge past a single point? �t=0. 6 seconds
Potential Difference
Potential Difference CHARGE PUMP
Electric Circuits �Electric Circuit: Any closed loop or conducting path allowing electric charges to flow. �All circuits must have two things: 1. Charge pump (to increase electric potential) 2. Something to reduce the electric potential
Moving Electrons �Light Bulb Demo • Difference between plugged in and out
Checkpoint �What is electric current? �What is an electric circuit?
Transformation of Energy r to o M Po sit ive Ch a rg e Po s sit iv e Ch ar . ge n Ge s
Infinite Energy Idea �Could a machine like this produce an infinite cycle of energy? Why? �Where is the energy lost?
Bellringer � DO STOP WORK
Objectives �Recreate Ohm’s discovery, and practice its application. �Learn how to draw schematic diagrams of electrical circuits. �Learn about “electrical friction” in long wires and other objects
Updates �Last Exam • 3 -4 points behind last year…not too bad • Corrections due this Friday �Science Learning Center • Below an 80 �Physics Club
Midterm Analysis �Zero if missing Grade vs. Study Time 90 85 Study time (hours) 0. 5 (0 -1) 1. 75 (1 -2. 5) 3. 75 (2. 5 -5) Average Score 57. 2857142 9 72. 4 84. 3333333 3 80 75 70 65 R 2 = 0, 9948 60 55 50 45 0 0, 5 1 1, 5 2 2, 5 3 3, 5 4
Predicted Study Time 0. 1 1 2 3 4 5 6 7 8 9 10 11 12 13 Predicted Grade 35. 47695 66. 076 75. 28723 80. 67546 84. 49847 87. 46382 89. 88669 91. 9352 93. 7097 95. 27492 96. 67505 97. 94163 99. 09792 100. 1616 Midterm Analysis Predicted Grade vs Study time 110 100 90 80 70 60 R 2 = 1 50 40 30 0 2 4 6 8 10 12 14
Energy Lost in Wires �Just like friction in mechanics, electric circuits have friction that cause energy to be lost. It is called “Resistance”
Ohm’s Law �Around 1825 Ohm was experimenting with electricity when he noticed an important trend between the current in a circuit and the voltage.
Investigating Ohm’s Law � For the sake of science we’ll recreate Ohm’s experiment to see if we can come up with Ohm’s Law on our own! • At the time (1820 s) German scientists didn’t believe in experiments. They thought the universe was so well ordered that you could find the scientific truth through deduction and reason. • “Web of Naked Fancies”
Discovering Ohm’s Law �Record this data! �Supplies: • • Voltmeter Ammeter Wires Batteries
Ohm’s Law �
Resistance �The resistance of an object in a circuit can be thought of like a frictional force because it makes it harder for the electrons to move.
Resistance Demos �How can we tell that electrical energy is being “lost” due the resistance of these objects? �Hotdog Demo �Pickle Demo
Example �
Practice � What is the current running through a 100 Ohm motor that is connected to a 120 V source? � 1. 2 A � What is the voltage across a hotdog that has a resistance of 10 Ohms and has 0. 2 amps running through it? � 2 V
Schematics �http: //phet. colorado. edu/en/simulation/circu it-construction-kit-dc
Schematics �The easiest way to describe the different parts of a circuit is with a Schematic �A schematic is a diagram that symbolically represents and simplifies a circuit
Schematics �Different symbols are used for different parts of a circuit �The symbols you need to know are found on your reference table
Schematic Symbols
Bellringer � What are the circuit elements in the schematic? � What is the current going through the light bulb if 10 C pass through it in 2 s? � What is the resistance of the bulb if it has a potential difference of 5 V?
Updates �Last Exam • 3 -4 points behind last year…not too bad • Corrections due this Friday �Science Learning Center • Below an 80 �Physics Club
Midterm Analysis �Zero if missing Grade vs. Study Time 90 85 Study time (hours) 0. 5 (0 -1) 1. 75 (1 -2. 5) 3. 75 (2. 5 -5) Average Score 57. 2857142 9 72. 4 84. 3333333 3 80 75 70 65 R 2 = 0, 9948 60 55 50 45 0 0, 5 1 1, 5 2 2, 5 3 3, 5 4
Predicted Study Time 0. 1 1 2 3 4 5 6 7 8 9 10 11 12 13 Predicted Grade 35. 47695 66. 076 75. 28723 80. 67546 84. 49847 87. 46382 89. 88669 91. 9352 93. 7097 95. 27492 96. 67505 97. 94163 99. 09792 100. 1616 Midterm Analysis Predicted Grade vs Study time 110 100 90 80 70 60 R 2 = 1 50 40 30 0 2 4 6 8 10 12 14
� The positive side of the battery is the longer end. � To show the current through the circuit you draw arrows showing which ways positive charges would flow. Schematics
Schematic Practice �If the diagram to the right has a 1. 5 V battery hooked up to it, why won’t the light turn on?
Schematic Practice �
Schematic Practice � Name all the elements in this circuit. � 3 cell battery � Ammeter � Resistor � Voltmeter � Wires
Bellringer � DO STOP WORK
Bellringer � What are the circuit elements in the schematic? � What is the current going through the light bulb if 10 C pass through it in 2 s? � What is the resistance of the bulb if it has a potential difference of 5 V?
Updates �SLC tomorrow • Below an 80 �Test analysis and correction due this Friday �Dance this Friday
Objectives �Review your schematics from last night �Know how to use a multi-meter to measure voltage and current �Start Lab
Picture Practice �On 11. page 603 answer questions 8, 9, and
Measuring Current �You measure current with an “Ammeter” �Current is how much charge is going through a loop of a circuit so you must connect the ammeter in the loop of the circuit.
Measuring Current
Measuring Potential Difference (Voltage) �You measure potential difference (voltage) with a “Voltmeter”. �When you measure voltage you measure between two points across an object in the circuit.
Measuring Voltage
Checkpoint 1. 2. 3. Draw a circuit with a battery and a resister. Also add an ammeter and a voltmeter. Why does an ammeter become part of the loop? Why doesn’t a voltmeter become part of the loop?
Multi-Meter �Amps • Red lead goes into top red port. • Turn knob to “ 10 A” (DCA) �Volts • Red lead goes into lower red port. • Turn knob to “ 20” (DCV)
Lab �Start lab to practice your measuring skills �Change . 0005 to. 00032
� Draw a circuit with a battery, a light bulb, an ammeter, and a voltmeter that is measuring the potential difference across the light bulb. Bellringer DO STOP WORK
Updates �SLC Today • Below an 80 �Corrections and Analysis due tomorrow. �Dance tomorrow night • Good songs? �Volleyball tournament next week!
Objectives �Be able to calculate the resistivity of a wire.
Resistance in the Wires �In schematics we will ignore the resistance in the wires. (Much like we ignore air resistance). �But this will not always be the case.
Resistance in a Wire �In real life it is often important to know how much voltage you lose due to resistance in a wire. �It is easy to calculate!
Resistance in a Wire � L A
Resistivity � Resistivity is a property of each material. � It is a constant number that is different for each material.
Example �
Practice �
� Draw a circuit with a battery, a light bulb, an ammeter, and a voltmeter that is measuring the potential difference across the light bulb. Bellringer DO STOP WORK
Updates �SLC Today • Below an 80 �Corrections and Analysis due tomorrow. �Dance tomorrow night • Good songs? �Volleyball tournament next week!
Objectives �Demo �Be able to solve regents problems
Labs
Variable Resistor Demo �A variable resistor or a slide resistor is a very handy device. �It allows you to change the resistance of an object to any resistance in a set range. �Examples: Dim light switches, volume knobs, fan speed, heaters, etc.
Variable Resistor Schematic
Practice
�What is the resistance in the circuit below? � 5 ohms Bellringer DO STOP WORK
Updates � SLC • 5: 30 detentions!!! � Dance • Last chance to ask that special someone � Labs • Hand them in � Test Analysis and Corrections • Zero for test grade if not here � HW L A
Objectives �Collect �Learn labs and review homework how electrical power is calculated and use it to solve problems and relate it to everyday items.
Power �Power, still measured in Watts, is the rate at which energy is transferred. �Most appliances, such as a hair dryer are rated in watts.
Power � It is more common to use P=VI when working with electricity, so we tend to use this equation when solving for the power of a part of a circuit.
Power �
Example �How much power does an oven draw from a circuit breaker if the oven has a potential difference of 220 V and draws 40 amps of current? �P=VI �P=220 V*40 A �P=8, 800 Watts
Practice �How much electrical current does a clothing iron use that draws 1, 600 W and has a potential difference of 120 V? �P=VI � 1, 600 W=120 V*I �I=13. 33 Amps
Practice �
Circuit Breakers � Circuit breakers are an engineering marvel that prevent billions of house fires � When an appliance is trying to draw a dangerous amount of current from a circuit breaker it “trips”, or disconnects itself from the circuit, causing all current to stop.
Circuit Breakers
Tripping Breakers �A breaker is easily reset by just moving the switch. �If a breaker continually trips it means you must go and unplug something from that circuit, or that the circuit is corrupted (improperly grounded, or shorted)
Homework 1. 2. 3. Find a household appliance (hair dryer, oven, washing machine, hair straightener or curler, Xbox, TV, laptop, etc. ) and figure out its power, current, voltage, and resistance. Go look at your circuit breaker, and find out what is the largest and smallest breaker in your home. Calculate the maximum number of amps you can have coming into your house at one time.
Bellringer �What is the power of a speaker that draws 2 amps of current and 120 volts? � 240 W DO STOP WORK
Updates � Labs: Missing • They should replace the wires. � Test Analysis and Corrections • Missing and redos � No physics club this week � SLC this Thursday • Below an 80 on last exam � Volleyball this Friday
Objectives �Be able to solve electrical power problems �Understand be able to calculate the electrical energy of a circuit.
Electricity in your home. �What appliance did you analyze? �How powerful was it? �What was your weakest circuit breaker? �What was your strongest circuit breaker? �What is the maximum current you can have coming into your house?
Practice �On page 601 in the textbook read through “Example problem 1” alone. �Then answer questions 1 -7 with a partner.
Answers page 601 1. 2. 3. 4. 5. 6. 7. 24 W 0. 60 A 63 W 25, 000 J 40 A 0. 30 A The power increases by a factor of 6
Work �As always work is the change in energy. �Now we’ll focus on the change in electrical work instead of the change in mechanical work.
Work �
Example �How much electrical energy is used by a 300 Watt blow-dryer that is used for 2 minutes? �W=Pt �W=300 W*120 s �W=36, 000 Joules
Practice � How much energy is used by 230 W bass amp that is playing on full volume for 3, 600 seconds that is plugged into a 120 V outlet? � 828, 000 J � What is the current going through the amp? � 1. 92 A � What is the resistance of the amp? � 62. 4Ω
Kilowatt hours �The SI unit of energy is Joule, but in RL we use “Kilowatt Hours” to buy energy from the energy company. �W=Pt, or Joule=Watt second � 1, 000 Watts are in 1 Kilowatt � 3, 600 seconds in 1 hour � 3, 600, 000 Joules = 1 Kilowatt Hour
Light Bulbs
Bellringer �What is the power of a speaker that draws 2 amps of current and 120 volts? � 240 W DO STOP WORK
Updates � Labs: Missing • They should replace the wires. � Test Analysis and Corrections • Missing and redos � No physics club this week � SLC this Thursday • Below an 80 on last exam � Volleyball this Friday
Objectives �Be able to solve electrical power problems �Understand be able to calculate the electrical energy of a circuit.
Electricity in your home. �What appliance did you analyze? �How powerful was it? �What was your weakest circuit breaker? �What was your strongest circuit breaker? �What is the maximum current you can have coming into your house?
Example �
Practice �Page 611 answer questions 26 to 30, skip 29 c • Assume these machines are 100% efficient �Page 613 answer questions 31 to 33
Answer page 611 a. 8. 0 A 27. a. 1. 2 A 28. a. 1, 300 J 29. a. 20 A 30. 1. 1 hours 26. b. 29, 000 J b. 16, 000 J b. 4, 700 J b. 130, 000 J c. 29, 000 J
Answer page 613 a. 1. 8 k. W b. 270 k. Wh 32. a. 0. 0096 A b. 1. 1 W 33. 9. 5 h 31. c. $32. 40 c. $0. 10
Bellringer � How much electrical energy is used by a 10 ohm resistor that is connected to a 12 volt battery for 15 seconds? � 216 Joules DO STOP WORK
Updates �Labs: Missing �Test Analysis and Corrections • Missing and redos �No physics club this week �SLC this Thursday • Below an 80 on last exam �Volleyball this Friday
Objectives �Go over homework. Be a master of electrical energy. �Investigate the two different types of circuits, and figure out which kind is used in your house.
Answer page 611 a. 8. 0 A 27. a. 1. 2 A 28. a. 1, 300 J 29. a. 20 A 30. 1. 1 hours 26. b. 29, 000 J b. 16, 000 J b. 4, 700 J b. 130, 000 J c. 29, 000 J
Answer page 613 a. 1. 8 k. W b. 270 k. Wh 32. a. 0. 0096 A b. 1. 1 W 33. 9. 5 h 31. c. $32. 40 c. $0. 10
Types of Circuits �There are two types of circuits 1. Series Circuits – when the current only has one way to flow 2. Parallel Circuits – when the current has two or more ways to flow
Series Circuit
Parallel Circuit
Measuring �When you measure the current you wire the ammeter in series �When you measure voltage you wire the voltmeter in parallel
Lab – “Running Some Wires” �You and your partners will be responsible for investigating which is the most efficient way to wire a house.
Things I Learned Since Yesterday � 20 Watts to power the Brain � 715 new planets discovered in our galaxy
Bellringer � An electric heater uses 32, 400, 000 J of energy each day. 1. How much energy is used over 30 days? 2. Convert that to k. Wh. 3. At $0. 12 per k. Wh, how much does it cost to operate the heater for these 30 days? DO STOP WORK
Solution �
Updates �Missing Labs and HWs �Science Learning Center on Thursday �Volleyball on Friday �Pass up labs �Last night’s homework
Types of Circuits �There are two types of circuits 1. Series Circuits – when the current only has one way to flow 2. Parallel Circuits – when the current has two or more ways to flow
Objectives �Be able to solve for the total and individual voltage, current, and resistance of series circuits.
Mountain Runoff
Series Circuit �Why must all the light bulbs be plugged in for them to shine? �Charge cannot be created or destroyed and since the charge only has one path to flow, all of it must flow through both light bulbs.
Series Circuit �
Series Circuit �The energy of each light bulb is proportional to the potential difference of the light bulb. �The total voltage from the battery is split up over each element of the circuit.
Series Circuit �From the river model, you know that the height from sea level to the top of the mountain equals the height that the water drops. �The potential difference across the battery equals the sum of the potential differences across lamp 1 and lamp 2.
Series Circuit �
Series Circuit �
Series Circuit �
Series Circuit �
Series Circuits �
� Example
� Example
Practice Problems � Page 5. 6. 7. 8. 626 #’s 1 -4 What is the total voltage of the batteries? What is the equivalent resistance in this circuit? What is the current? What is the voltage across each resistor?
�What is the total current in the circuit? �I=0. 0005 A Bellringer DO STOP WORK
Objectives �Be able to find the individual and total current, resistance, and voltage of a parallel circuit. �Be able to combine what you know about series and parallel to find the total resistance, current, and voltage.
Homework �Take out your homework from last night
Practice Problems � Page 5. 6. 7. 8. 626 #’s 1 -4 What is the total voltage of the batteries? What is the equivalent resistance in this circuit? What is the current? What is the voltage across each resistor?
Answers 1. 2. 3. 4. 66Ω, 1. 9 A 32Ω, 2. 3 A 200Ω a. It will increase b. It will decrease c. No; it does not depend on the resistance
Answers 5. 6. 7. 24 V 8Ω 3 A 9 volts 8. 6 volts 9 volts
Parallel Circuits �Picture a mountain that has multiple rivers running down it all with different amounts of water. �Same drop in height over each path, but can have different amounts of water
Parallel Circuits �Thinking of the mountain, in parallel circuits the total current is the sum of the currents through each path, and the potential difference across each path is the same.
Parallel Circuits �
Example Draw and label this diagram (make it big) � What is the voltage across each resistor? � What is the current in each part of the circuit? � What is the total current?
Parallel Circuits �So we know how to find the total current and the total potential difference in a parallel circuit. What about the total resistance in a parallel circuit?
Parallel Circuits � 0. 1 A 0. 2 A 0. 05 A
� But Parallel Circuits 90+45+180 doesn’t equal 25. 7! � That’s because placing 2 or more resistors in parallel always decreases the equivalent resistance of a circuit. � The resistance decreases because each new resistor provides an additional path for current, thereby increasing the total current while the potential difference remains unchanged.
Parallel Circuits �
Bucket Demo
Example �
Practice �On page 633 answer questions 14 -16
Answers to page 633 �
Homework �Numbers 1 -23 in the series and parallel circuits packet.
Example #2 A. B. C. D. What is the potential difference across each resistor if the battery is 12 V? What is the equivalent resistance of the circuit? What is the current across each branch of the parallel circuit? What is the total current moving through the parallel circuit?
Objectives �Be able to find the individual and total current, resistance, and voltage of a parallel circuit. �Be able to combine what you know about series and parallel to find the total resistance, current, and voltage.
The Next Level Circuit �What the heck is going on over there?
Series-Parallel Circuits �To solve a seriesparallel circuit you must “convert” it into a simple series circuit.
� Example
� Example
Series-Parallel Circuit Activity � With a partner solve for the total resistance, total current, and total potential difference of each of the circuits. � Once you think you’ve found the right answer go check it by throwing the switch in the back and reading the ammeter. � See me once you’re done.
Homework �Complete the first full page of this packet for homework this weekend. �Remember you will have a test next week (Tuesday or Wednesday) so you should start to study too.
�What is the equivalent resistance in the circuit? �R=25. 7 Ohms Bellringer DO STOP WORK
Objectives �Be able to combine what you know about series and parallel to find the total resistance, current, and voltage. �Clear up any problems you have when solving part two type questions about electric current.
Test! �Electric Current Test Tuesday and Wednesday. � 50 pts: multiple choice � 50 pts: long answer
Test Topics �Current, Resistance, and Voltage �Ohm’s Law �Resistivity �Electrical Power �Electrical Energy �Circuit Diagrams �Series and Parallel Circuits
Homework �Let’s go over it. �Finish the packet for homework tonight.
Series-Parallel Circuit Activity � With a partner solve for the total resistance, total current, and total potential difference of each of the circuits. � Once you think you’ve found the right answer go check it by throwing the switch in the back and reading the ammeter. � See me once you’re done.
Bellringer �How many k. Wh is 1, 000 Joules? � 0. 278 k. Wh DO STOP WORK
Objectives �Practice part two type questions for tomorrow’s test. �Review any last minute concerns
Homework �Let’s review last night’s homework. �Tonight’s homework is to study for tomorrow’s test.
Station Problems � You will work with a partner to rotate through six example part two type questions. � Team with the most points at the end wins points on tomorrow’s exam. � If two teams tie they can either split the points or face off in one round of rock paper scissors.
Live Wire �Read page 640 in the textbook and answer the following questions 1. How do circuit breakers stop house fires? 2. Why are small electronics and computers prone to over heating?
A Taste of College �Circuits �https: //www. youtube. com/watch? v=a 6 Yy. E eq. FFDA �The electric company �https: //www. youtube. com/watch? v=YNk. D 9 TZtdb. Y
Concepts �On page 642 answer questions 36 to 41
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