HSC Physics Module 8.3 Electrical Energy in the Home

Transcription

1 HSC Physics Module 8.3 Electrical Energy in the Home

2 8.3 Electrical Energy in the Home (30 indicative hours) Contextual Outline Electricity is an essential energy source for modern living. Disruption to supply or isolation can lead to the development of alternative methods of obtaining this essential energy resource. For electrical energy to be useful it must be harnessed through the use of an electrical circuit and an energy-converting appliance. As electricity became increasingly used as the main power supply in homes and electrical appliances became an integral part of daily life for many Australians, the dangers associated with electricity became more prominent. Voltages as low as 20 volts can be dangerous to the human body depending on the health of the person and length of time of contact with the current. Safety devices in household appliances and within the electric circuits in the home can prevent electrical injury or assist in reducing the potential for electric shock. This module increases students understanding of the history, nature and practice of physics and the applications and uses of physics. Assumed Knowledge Domain: knowledge and understanding: Refer to the Science Stages 4 5 Syllabus for the following: 5.6.3a design, construct and draw circuits containing a number of components 5.6.3b describe voltage, resistance and current using analogies 5.6.3c describe qualitatively, the relationship between voltage, resistance and current 5.6.3d compare advantages and disadvantages of series and parallel circuits Skills Skill development focuses on: Developing scientific research and communication skills in extracting information, drawing and writing effectively. Planning and carrying out procedures to obtain first hand data. Developing skills in manipulating a variety of electrical components and measuring devices. Developing skills in analysing information to identify patterns and trends and to use models to explain phenomena or to make predictions. Values and Attitudes During this module, teaching/learning activities should allow students to reflect on personal and societal choices and responsibilities about energy production and consumption. There should be an enhanced understanding of the impacts of the provision of electrical energy on the environments from which the necessary resources are obtained and those environments in which electrical generation and transmission occur. Often the decisions Governments make are compromises e.g. coal mining is allowed if associated with conservation projects and these issues could provide opportunities for class debate. Students should be provided with opportunities to develop a better understanding of the need to provide a balance between the electrical energy needs of people and limited resources available to produce that energy. The importance of research into renewable, low impact sources of energy should be raised. They should also appreciate the imbalance that occurs across and between societies in the availability and consumption of electrical energy. Open class discussions centred round Gospel values should challenge the students to formulate their own opinions about equity, conservation and respect for the opinions of others. 2

3 Concept Map CHARGE STATIC ELECTRICITY HISTORICAL DEVELOPMENT ELECTRIC POTENTIAL CURRENT FIELDS DIFFERENCE ELECTRICITY AC/DC RESISTANCE SOURCES OF PD CIRCUITS APPLICATIONS & TECHNOLOGY SAFETY HOUSEHOLD ELECTRICITY ENERGY CONSUMPTION 3

4 Electrical Energy in the Home Module Plan Module Length: 7 weeks Focus Area Time Concept Resources Practical 1. Society has become increasingly dependent on electricity over the last 200 years 2. One of the main advantages of electricity is that is can be moved with comparative ease from one place to another through electric circuits 1 1 discuss how the main sources of domestic power have changed over time 2 assess some of the impacts of changes in, and increased access to, sources of power for a community 3 discuss some of the ways in which electricity can be provided in remote locations 1 1 describe the behaviour of electrostatic charges and the properties of the fields associated with them 2 define the unit of electric charge as the coulomb 3 define the electric field as a field of force with a field strength equal to the force per unit charge at that point F E q 2 4 define electric current as the rate at which charge flows (coulombs/second or amperes) 5 identify that current can be either direct with the net flow of charge carriers moving in one direction or alternating with the charge carriers moving backwards and forwards periodically 2 6 describe electric potential difference (voltage) between two points as the change in potential energy per unit charge moving from one point to the other (joules/coulomb or volts) 7 discuss how potential difference changes at different points around a DC circuit UP: 149 NS: The EM link Contexts I: pp UP: Contexts I: pp Dyett: Humphrey s Set 36 UP: Contexts I: pp Dyett: Humphrey s Sets UP: Contexts I: pp Dyett: (Act 1) identify data sources, gather, process and analyse secondary information about the differing views of Volta and Galvani about animal and chemical electricity and discuss whether their different views contributed to increased understanding of electricity. 1 (Exp 2) present diagrammatic information to describe the electric field strength and direction: between charged parallel plates. about and between a positive and negative point charge 2 (Act 3) solve problems and analyse information using E = F /q 3 (Exp 4) plan, choose equipment for and perform a first-hand investigation to gather data and use the available evidence to show the relationship between voltage across and current in a DC circuit. 4 (Exp 5) plan, choose equipment for and perform a first-hand investigation to gather data and use the available evidence to show the variations in and potential difference between different points around a circuit 4

5 Focus Area Time Concept Resources Practical 2 8 describe the difference between conductors and insulators 9 Define resistance as the ratio of voltage to current for a particular conductor UP: Contexts I: pp (Act 6) gather and process secondary information to identify materials that are commonly used as conductors to provide household electricity 3. Series and parallel circuits serve different purposes in households R V I 10 explain qualitatively and quantitatively that resistance is related to potential difference 11 describe qualitatively how each of the following affects the movement of electricity through a conductor: length cross sectional area temperature material 3 1 identify the difference between series and parallel circuits. 2 compare parallel and series circuits in terms of voltage across components and current through them 3 identify the uses of ammeters and voltmeters 4 explain why ammeters and voltmeters are connected differently in a circuit 5 explain why there are different circuits for lighting, heating and other appliances in a house UP: Contexts I: pp Dyett: Humphrey Sets (Exp 7) plan, choose equipment or resources for and perform first-hand investigations to gather data and use available evidence to compare measurements of current and voltage in series and parallel circuits in computer simulations or hands-on equipment 2 (Exp 8) plan, choose equipment or resources for process information and perform a first hand investigation to construct a simple model household circuits using electrical components 4. The amount of energy transformed in an appliance is related to the power rating of an appliance and the length of time it is used 3 1 explain that power is the rate at which energy is transformed from one form to another 2 identify the relationship between power dissipated, potential difference and current 3 identify that the total amount of energy used depends on the length of time the current is flowing and can be calculated using: Energy = VIt 4 explain why the kilowatthour is used to measure domestic electricity consumption rather than the joule UP: Contexts I: pp Humphrey Set 42 1 (Exp 9) perform a first-hand investigation, gather information and use available evidence to demonstrate the relationship between current, voltage and power for a model 6V to 12V electric heating coil 2 (Act 10) solve problems and analyse information using P=VI and Energy = VIt 5

6 Focus Area Time Concept Resources Practical 5. Electric currents also produce magnetic fields and these fields are used in different devices in the home 3 1 describe the behaviour of the magnetic poles of bar magnets when they are brought close together 2 define the direction of the magnetic field at a point as the direction of force on a very small north magnetic pole when placed at that point 3 describe the magnetic field around pairs of magnetic poles 3 4 describe the production of a magnetic field by an electric current in a straight current-carrying conductor and describe how the right hand grip rule can determine the direction of current and field lines 5 compare the nature and generation of magnetic fields by solenoids and a bar magnet UP: Contexts I: pp Dyett: UP: Dyett: Humphrey Set 45 1 (Exp 11) plan, choose equipment or resources for, and perform a firsthand investigation build an electromagnet 2 (Exp 12) perform a first-hand investigation to observe magnetic fields by mapping lines of force: around a bar magnet surrounding a straight DC current-carrying conductor a solenoid present information using and to show the direction of a current and direction of a magnetic field. 3 (Act 13) identify data sources, gather, process and analyse information to explain one application of magnetic fields in household appliances. 6. Safety devices are important in household circuits 3 1 discuss the dangers of an electric shock from both a 240 volt AC mains supply and various DC voltages, from appliances, on the muscles of the body 2 describe the functions of circuit breakers, fuses, earthing, double insulation and other safety devices in the home Contexts I: pp

7 Preliminary Physics C2: Electrical Energy in the Home Activity 1: History of Electricity Aim: To identify data sources, gather, process and analyse secondary information about the differing views of Volta and Galvani about animal and chemical electricity and discuss whether their different views contributed to increased understanding of electricity. o accessing information from a range of resources, including popular scientific journals, digital technologies and the Internet (12.3a) o practising efficient data collection techniques to identify useful information in secondary sources (12.3b) o summarising and collating information from a range of resources (12.3d) o identifying practising male and female Australian scientists, and the areas in which they are currently working and in formation about their research (12.3e) o evaluate the validity of first-hand and secondary information and data in relation to the area of investigation (12.4d) o assess the reliability of first-hand and secondary information and data by considering information from various sources (12.4e) o selecting and using appropriate text types or combinations thereof, for oral and written presentations (13.1a) o selecting and using appropriate methods to acknowledge sources of information (13.1c) Write a 400 word report on this dot point. Preliminary Physics C2: Electrical Energy in the Home Experiment 2: Mapping Equipotential Lines Aim: To present diagrammatic information to describe the electric field strength and direction between charged parallel plates and about and between a positive and negative charge. o using symbols and formulae to express relationships and using appropriate units for physical quantities (13.1d) o using a variety of pictorial representations to show relationships and present information clearly and succinctly (13.1e) o selecting and drawing appropriate graphs to convey information and relationships clearly and accurately (13.1f) 7

8 Method 1. The diagram on the right is set up. 2. Using the probe, trace a line along the paper where the voltage remains the same. Mark this line using a lead pencil. ENSURE THAT THE PAPER STAYS WET AT ALL TIMES! 3. Repeat steps 1 and 2 until several equipotential lines (8) are drawn. Record the voltage of each line. 4. Repeat steps 1-3 for the electrodes shown below: Discussion (1) How can we find the electric field from the equipotential lines? Draw the electric field for each pair of electrodes. (2) What is the purpose of the salt solution? (3) Suggest what happens on the inside of the circle in electrode pairs 3 & 5 (4) What does your answer to (3) tell you about how charge is conducted? (5) What industrial applications could there be for your answers to questions (3) and (4)? (6) Calculate the value of the electric field in each case that you studied. (7) What is charge? (No textbook definitions please, just your own ideas about what charge is.) Preliminary Physics C2: Electrical Energy in the Home Activity 3: Electric Fields Aim: To solve problems and analyse information using E = F /q o identify trends, patterns and relationships as well as contradictions in data and information (14.1a) o identify and explain how data supports or refutes an hypothesis, a prediction or a proposed solution to a problem (14.1c) o use models, including mathematical ones, to explain phenomena and/or make predictions (14.1f) o design and produce creative solutions to problems (14.3a) o propose ideas that demonstrate coherence and logical progression and include correct use of scientific principles and ideas (14.3b) o apply critical thinking in the consideration of predictions, hypotheses and the results of investigations (14.3c) 8

9 o Formulate cause and effect relationships (14.3d) Do Humphrey s Set 36 9

10 Preliminary Physics C2: Electrical Energy in the Home Experiment 4: DC Circuits. Aim: To plan, choose equipment for and perform a first-hand investigation to gather data and use the available evidence to show the relationship between voltage across and current in a DC circuit. o demonstrate the use of the terms dependent and independent to describe variables involved in the investigation (11.2a) o identify variables that needed to be kept constant, develop strategies to ensure that these variables are kept constant, and demonstrate the use of a control (11.2b) o design investigations that allow valid and reliable data and information to be collected (11.2c) o describe and trial procedures to undertake investigations and explain why a procedure, a sequence of procedures or the repetition of procedures is appropriate (11.2d) o identifying and/or setting up the most appropriate equipment or combination of equipment needed to undertake the investigation (11.3a) o carrying out a risk assessment of intended experimental procedures and identifying and addressing potential hazards (11.3b) o carrying out the planned procedure, recognising where and when modifications are needed and analysing the effect of these adjustments (12.1a) o identifying and using safe work practices during investigations (12.1d Part A: CRO Both types of current will be displayed on the CRO. Part B: Circuit 1. Set up the circuit on the right. Set the power supply to 12V DC. 1. Measure the voltage and current through the resistor at several different settings of the rheostat. Discussion (1) Does a resistor treat AC different from DC? Explain your answer. (2) Why is DC more useful for circuits? (3) Explain the following terms: transformer, rectifier, bridge circuit. 10

11 Preliminary Physics C2: Electrical Energy in the Home Experiment 5: Voltage Aim: To plan, choose equipment for and perform a first-hand investigation to gather data and use the available evidence to show the variations in and potential difference between different points around a circuit o demonstrate the use of the terms dependent and independent to describe variables involved in the investigation (11.2a) o identify variables that needed to be kept constant, develop strategies to ensure that these variables are kept constant, and demonstrate the use of a control (11.2b) o design investigations that allow valid and reliable data and information to be collected (11.2c) o describe and trial procedures to undertake investigations and explain why a procedure, a sequence of procedures or the repetition of procedures is appropriate (11.2d) o identifying and/or setting up the most appropriate equipment or combination of equipment needed to undertake the investigation (11.3a) o carrying out a risk assessment of intended experimental procedures and identifying and addressing potential hazards (11.3b) o carrying out the planned procedure, recognising where and when modifications are needed and analysing the effect of these adjustments (12.1a) o identifying and using safe work practices during investigations (12.1d Method 1. Set up the following circuit: 2. Measure the voltage between different points as given in the results table. Results Table Voltage between a b c d e f g h a b c d e f g h Discussion (1) Is there more than 12V in the circuit? Why? why not? (2) Why is there no potential difference between points a and c? (3) What is the voltage across the switch when it is open? Explain your answer. 11

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13 Preliminary Physics C2: Electrical Energy in the Home Activity 6: Conductors Aim: To gather and process secondary information to identify materials that are commonly used as conductors to provide household electricity o accessing information from a range of resources, including popular scientific journals, digital technologies and the Internet (12.3a) o extracting information from numerical data in graphs and tables as well as written and spoken material in all its forms (12.3c) o summarising and collating information from a range of resources (12.3d) o identifying practising male and female Australian scientists, and the areas in which they are currently working and in formation about their research (12.3e) o identify and apply appropriate mathematical formulae and concepts (12.4b) o evaluate the validity of first-hand and secondary information and data in relation to the area of investigation (12.4d) o assess the reliability of first-hand and secondary information and data by considering information from various sources (12.4e) o assess the accuracy of scientific information presented in mass media by comparison with similar information presented in scientific journals (12.4f) o selecting and using appropriate methods to acknowledge sources of information (13.1c) Write a 300 word report identifying commonly used conductors for household electricity. 13

14 Preliminary Physics C2: Electrical Energy in the Home Experiment 7: Series & Parallel. Aim: To plan, choose equipment or resources for and perform first-hand investigations to gather data and use available evidence to compare measurements of current and voltage in series and parallel circuits in computer simulations or hands-on equipment You must devise a method using equipment listed below and/or any other reasonable equipment. Equipment Available Ammeters & voltmeters Resistors, wires Power supply Computer with Crocodile Clips installed. You should consider the following points: Does the experiment satisfy the aim above? The safety of the experiment. Any safety notes need to be explicit. Design your own result table. Have you repeated the experiment several times to validate the results and to calculate a mean? Did you show your working? What are some possible sources of error? How could these errors be minimised or eliminated? 14

15 Preliminary Physics C2: Electrical Energy in the Home Experiment 8: Modelling Household Circuits. Aim: To plan, choose equipment or resources for process information and perform a first hand investigation to construct model household circuits using electrical components o describe and trial procedures to undertake investigations and explain why a procedure, a sequence of procedures or the repetition of procedures is appropriate (11.2d) o identifying and/or setting up the most appropriate equipment or combination of equipment needed to undertake the investigation (11.3a) o carrying out a risk assessment of intended experimental procedures and identifying and addressing potential hazards (11.3b) o carrying out the planned procedure, recognising where and when modifications are needed and analysing the effect of these adjustments (12.1a) o identifying and using safe work practices during investigations (12.1d) You must devise a method using equipment listed below and/or any other reasonable equipment. Make circuits that represent the following: Double pole light switch Electric kettle Electric blanket (with three heat settings) For each situation, construct and draw a circuit that satisfies the situation. Put at least one resistor in series with the power supply. Equipment Available Ammeters & voltmeters Resistors, wires Power supply You should consider the following points: Does the experiment satisfy the aim above? The safety of the experiment. Any safety notes need to be explicit. Design your own result table. Have you repeated the experiment several times to validate the results and to calculate a mean? Did you show your working? What are some possible sources of error? How could these errors be minimised or eliminated? 15

16 Preliminary Physics C2: Electrical Energy in the Home Experiment 9: Heating Coils Aim: To perform a first-hand investigation, gather information and use available evidence to demonstrate the relationship between current, voltage and power for a model 6V to 12V electric heating coil o carrying out the planned procedure, recognising where and when modifications are needed and analysing the effect of these adjustments (12.1a) o identifying and using safe work practices during investigations (12.1d) o using symbols and formulae to express relationships and using appropriate units for physical quantities (13.1d) o using a variety of pictorial representations to show relationships and present information clearly and succinctly (13.1e) o selecting and drawing appropriate graphs to convey information and relationships clearly and accurately (13.1f Method 1. Set up the circuit shown below: 12V V Heating Coil A 2. Measure the mass of water in a beaker. (the coil may already have a container) 3. Immerse the heating coil in the beaker of water 4. Measure the initial temperature of the water. 5. Turn the power on and measure the time it takes for the water heat up by 10 C. Discussion 1. Calculate the power rating of the heating coil. 2. Calculate the energy delivered to the coil. 3. Using the equation H=mc. T where c J/g/K for water, calculate the heat energy given to the water. Preliminary Physics C2: Electrical Energy in the Home Activity 10: Power and Energy Aim: To solve problems and analyse information using P=VI and Energy = VIt for a variety of situations o identify trends, patterns and relationships as well as contradictions in data and information (14.1a) o identify and explain how data supports or refutes an hypothesis, a prediction or a proposed solution to a problem (14.1c) o use models, including mathematical ones, to explain phenomena and/or make predictions (14.1f) o design and produce creative solutions to problems (14.3a) o propose ideas that demonstrate coherence and logical progression and include correct use of scientific principles and ideas (14.3b) o apply critical thinking in the consideration of predictions, hypotheses and the results of investigations (14.3c) o formulate cause and effect relationships (14.3d) 16

17 Do Humphrey s Set 42 17

18 Preliminary Physics C2: Electrical Energy in the Home Experiment 11: Electromagnets Aim: To plan, choose equipment or resources for, and perform a first-hand investigation to build an electromagnet o carrying out the planned procedure, recognising where and when modifications are needed and analysing the effect of these adjustments (12.1a) o identifying and using safe work practices during investigations (12.1d) You must devise a method using equipment available in the laboratory. You should consider the following points: Does the experiment satisfy the aim above? The safety of the experiment. Any safety notes need to be explicit. Design your own result table. Have you repeated the experiment several times to validate the results and to calculate a mean? Did you show your working? What are some possible sources of error? How could these errors be minimised or eliminated? Do you have a conclusion? After your results, you should provide a detailed discussion of the implications of the experiment. 18

19 Preliminary Physics C2: Electrical Energy in the Home Experiment 12: Mapping Magnetic Fields Aim: To perform a first-hand investigation to observe magnetic fields by mapping lines of force around a bar magnet; surrounding a straight DC current-carrying conductor; and of a solenoid and present information using or to show the direction of a current and strength and direction of a magnetic field. o carrying out the planned procedure, recognising where and when modifications are needed and analysing the effect of these adjustments (12.1a) o identifying and using safe work practices during investigations (12.1d) Method Part A: Mapping Magnetic Fields Around a Bar Magnet 1. Obtain two bar magnets, a plastic sheet and some iron filings. 2. Arrange the bar magnets such that two opposite poles are facing each other and are seperated by about 1 cm. Lay the plastic sheet over the magnets and gently sprinkle the iron filings over the magnets. 3. Record the pattern produced in your prac books. 4. Reverse the pole on one of the magnets. Repeat the procedure. Part B: Mapping Magnetic Fields Around a Current-Carrying Conductor 1. Wrap a wire in a plastic bag. 2. Pierce a hole in the middle of a large piece of cardboard. 3. Thread the wire through the hole in the cardboard. 4. Suspend the wire vertically so that the cardboard is horizontal. 5. Connect the wire to a power supply. 6. Sprinkle the iron filings around the cardboard. 7. Draw the pattern observed. Part C: Mapping Magnetic Fields Around a Solenoid Repeat part A using a single solenoid instead of the bar magnets. Discussion (1) What are some examples of magnetic materials? What do they have in common? (2) On the molecular level, what is a ferromagnet? How is this different to diamagnetism? (3) What is anti-ferromagnetism? Explain using diagrams. (4) What is the convention for the direction of magnetic fields? (5) How are magnetic fields and electric fields related? 19

20 Preliminary Physics C2: Electrical Energy in the Home Activity 13: Household Appliances Aim: To identify data sources, gather, process and analyse information to explain one application of magnetic fields in household appliance. o accessing information from a range of resources, including popular scientific journals, digital technologies and the Internet (12.3a) o extracting information from numerical data in graphs and tables as well as written and spoken material in all its forms (12.3c) o summarising and collating information from a range of resources (12.3d) o identifying practising male and female Australian scientists, and the areas in which they are currently working and in formation about their research (12.3e) o identify and apply appropriate mathematical formulae and concepts (12.4b) o evaluate the validity of first-hand and secondary information and data in relation to the area of investigation (12.4d) o assess the reliability of first-hand and secondary information and data by considering information from various sources (12.4e) o assess the accuracy of scientific information presented in mass media by comparison with similar information presented in scientific journals (12.4f) o selecting and using appropriate methods to acknowledge sources of information (13.1c) Write a 400 word report on this issue. 20