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BASIC ELECTRICITY Nicola Tesla: Mad Electricity LESSON 1 : CIRCUIT SYMBOLS Draw and identify the circuit symbol for a battery, lamp, switch, resistor, motor, and variable resistor. State that lamps, heaters and motors and buzzers convert electrical energy into other forms. LESSON 1 : CIRCUIT SYMBOLS Examine examples of circuit components and produce a poster matching pictures of components to their symbols and energy conversions. ELECTRICAL ENERGY CONVERTERS What are the energy conversions associated with each of these devices? Loudspeaker Microphone Hair straighter TV Lift going up Heater Lamp electrical sound sound electrical electrical heat electrical sound + light electrical kinetic + potential electrical heat electrical light + heat Now watch this short video: Electricity and circuits LESSON 2/3: PRACTICAL CIRCUITS - QUIZ BOARD LESSON 2/3: PRACTICAL CIRCUITS - TRAFFIC LIGHTS LESSON 2/3 – PRACTICAL CIRCUITS - ELECTROPLATING LESSON 4,5 ELECTRICAL MEASUREMENTS IN CIRCUITS State that an ammeter is used to measure current in Amps. Draw and identify the circuit symbol for an ammeter. Draw a circuit diagram showing the correct position of an ammeter in the circuit. State that current is a flow of charge and is measured in amperes State that an voltmeter is used to measure voltage in Volts Draw and identify the circuit symbol for a Voltmeter. Draw a circuit diagram showing the correct position of a voltmeter in the circuit. State that voltage is the electrical push and is measured in Volts. State that the voltage is the same for all components connected in parallel. LESSON 4 : ELECTRICAL MEASUREMENTS – SERIES CIRCUIT – XMAS TREE LIGHTS Xmas tree lights are wired in series – in a line one after the other. Connect three bulbs in series as shown in the diagram. Use retort stands as model tree! You will need: •Connecting wire •3 x Bulb holders with 2.5v lamps •6V battery •1 x retort stands and clamps •Wire strippers MEASURING CURRENTS IN THE CIRCUIT What is current? Programs / Virtual Int1 Physics / Practical Electricity / Current Watch as you are shown how to measure the currents in the circuit you have just built. Now go and measure the currents from the battery and through each of the lamps. Can you notice a pattern? The current is the same at all points at all points in the circuit video clip: How to use a multimeter MEASURING CURRENT Current is the flow of tiny electric charges around a circuit. An ammeter is used to measure the current through a circuit, measured in amperes (A) To connect an ammeter we have to break the circuit and put the ammeter in series with the other components. The size of a current in a series circuit is the same at all points in the circuit ?A 2A ?A 2A ?A 2A MEASURING VOLTAGES IN THE CIRCUIT Watch as you are shown how to measure the voltages in the circuit you have just built. Now go and measure the voltages across the battery and each of the lamps. Can you notice a pattern? The voltages in a series circuit add to equal the battery voltage (or very similar!) MEASURING VOLTAGE IN SERIES Voltage can be thought of as the 'push' it exerts on charges in the circuit. A bigger voltage means a bigger 'push', resulting in a larger current A voltmeter is used to measure voltage, in volts (V) Voltmeters are connected in parallel to either side of the component. The size of the voltage across the battery in a series circuit is equal to the sum of the voltages across the other components. 3V ?V 6V ?V 3V ?V LESSON 5 : ELECTRICAL MEASUREMENTS IN A PARALLEL CIRCUIT – STREET LIGHTS Street lights are wired in parallel and are controlled by a time switch driven by a clock. This turns the lights on and off at the correct time. Connect three bulbs in parallel as shown in the diagram. Use retort stands as model lamp posts. You will need: •Connecting wire •3 x Bulb holders with 6v lamps •6V battery •3 x retort stands and clamps •Wire strippers • What are the main advantages of wiring street lamps in parallel? MEASURING VOLTAGES IN THE CIRCUIT Watch as you are shown how to measure the voltages in the circuit you have just built. Now go and measure the voltages across the battery and each of the lamps. Can you notice a pattern? The voltages in a parallel circuit are all the same (or very similar!) MEASURING VOLTAGE The size of the voltage across the battery in a parallel circuit is equal to the voltages across the other components. ?V 6V ?V 6V ?V 6V MEASURING CURRENTS IN THE CIRCUIT Watch as you are shown how to measure the currents in the circuit you have just built. Now go and measure the currents from the battery and through each of the lamps. Can you notice a pattern? In a parallel circuit the current from the battery equals the sum of the currents through the lamps (or very similar!) MEASURING CURRENT IN A PARALLEL CIRCUIT In a parallel circuit: the size of the current from the battery equals the sum of the currents through each of the other components. 4A ?A 2A ?A 2A ?A 4A ?A video clip: Lighting Circuit ADVANTAGES OF WIRING STREET LAMPS IN PARALLEL: When bulbs are connected in parallel each bulb gets the full battery voltage. Each bulb lights with equal brightness. If one or more bulbs stop working or are removed the rest continue lighting. SERIES V PARALLEL SHOW-ME EXERCISE You will see statements appear that may apply to SERIES circuits or PARALLEL circuit. Which is it? SERIES PARALLEL These have no If one bulb breaks, the branches or junctions Can be turned on other bulbs in otherand off put more bulbs in they byIfayou single switch branches stay on. will be dimmer Switches be put into anywhere in can circuit asthe it iscircuit harder for the current to turn on and Thetosum of voltages across get through- the resistance off allhave or part ofisthe and branches is higher all These the components circuit. junctions equal to the voltage across oneorbulb breaks, all theIfcell battery you put theIfothers go more out. bulbs in Thethey size of current flowing will stay bright in different parts of the circuit can be different. AMMETER AND VOLTMETER EXERCISES Redraw each of the following diagrams and on each, Add a meter to find the voltage across component E Add a meter to find the current through component F Now complete the exercise, “Measuring current and voltage in series and parallel circuits” CURRENT AND VOLTAGE CLIPS Current and voltage in a circuit. Current and Voltage in a series and parallel circuit LESSON 7/8: OHM’S LAW RESISTANCE Conduct an experimental investigation of the relationship between voltage and current through a resistor. State that voltage/current = constant State that the “constant” is called the “resistance” State that resistance is a measure of the opposition to the flow of current in a circuit. State that resistance = voltage/current is called Ohm’s law. Calculate resistance using Ohm’s law INVESTIGATION: HOW DOES CHANGING THE VOLTAGE AFFECT THE CURRENT ? In this experiment you will use battery voltage to push current through a resistor. You will use an ammeter and a voltmeter to find how changing the voltage affects the current. Follow the instructions on the worksheet, “Voltage, Current and Resistance” OHMS LAW 2 Number of batteries 1 2 3 4 Voltmeter reading (Volts) Ammeter Reading (Amps) voltage current OHM’S LAW - RESISTANCE An experimental investigation of the relationship between voltage and current through a resistor shows that voltage/current = constant. this is called Ohm’s Law The “constant” is called the “resistance”. Resistance is a measure of the opposition to the flow of current in a circuit. CALCULATING RESISTANCE FROM AMMETER AND VOLTMETER VALUES Calculate resistance using: voltage resistance = current Example: The current through a resistor is 0.1 amperes when the voltage across it is 12 volts. Calculate the resistance. 0.1A resistance = voltage current 12V = 12 0.1 = 120W OHMS LAW PRACTICE 1. A resistor has a voltage across it of 12 volts and a current through it of 2.5 amperes. Calculate the resistance of the resistor. Solution 2. A voltage of 6 volts is across a resistor where the current is 0.5 amperes. What is the value of the resistor? Solution 3. Calculate the resistance of a component when a voltage of 24 V causes a current of 0.1 amperes. Solution 5. A torch bulb is marked "6 V, 0.25 A". Calculate the resistance of the bulb. Practical Problems involving resistance Solution 1. A resistor has a voltage across it of 12 volts and a current through it of 2.5 amperes. Calculate the resistance of the resistor. resistance = voltage current 12 = 2.5 = 4.8 W Beath High School - Int 1 Physics 29 2. A voltage of 6 volts is across a resistor where the current is 0.5 amperes. What is the value of the resistor? resistance = voltage current 6 = 0.5 = 12 W 3. Calculate the resistance of a component when a voltage of 24 V causes a current of 0.1 amperes. resistance = voltage current 24 = 0.1 = 240 W 4. A torch bulb is marked "6 V, 0.25 A". Calculate the resistance of the bulb. resistance = voltage current 6 = 0.25 = 24 W LESSON 9: PRACTICAL PROBLEMS INVOLVING RESISTORS Draw and identify the circuit symbol for a resistor and a variable resistor. State that resistors convert electrical energy into heat energy. State that an ohmmeter is used to measure resistance. State that resistance is measured in ohms. State that an increase in resistance of a circuit leads to a decrease in the current in the circuit. Give two practical uses of resistors. PRACTICAL USES OF RESISTORS 1 The most common use for a resistor is simply to control the size of the current flowing in part of a circuit. The larger the resistance the smaller the current. The smaller the resistance the larger the current. Resistance is measured in units of ohms (Ω) Symbol for resistor: Symbol for variable resistor: PRACTICAL USES OF RESISTORS 2 Dimmer Switch Fan Speed Scaletrix controller Petrol Gauge Heating Element Radio volume control Skin Resistance – Lie Detector