30/04/2015 static electricity and electricity. static electricity lesson 1 30/04/2015

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30/04/2015 Static electricity and Electricity Slide 2 Static electricity Lesson 1 30/04/2015 Slide 3 Lesson 1+ 2 aims Static electricity Examples and uses of static electricity Electricity Circuits Voltage and current 30/04/2015 Slide 4 Static electricity Lesson 1 30/04/2015 Slide 5 Static electricity 30/04/2015 1.When two different insulating materials are rubbed together they become electrically charged. 2.Negative charges (electrons) rub off one material onto the other. The material which gains negative charges becomes negatively charged. The material which loses negative charges becomes positively charged. Slide 6 Static Electricity Slide 7 Only electrons move Both positive and negative charges are produced by the movement of electrons Positive charges do not move A positive static charge is caused by electrons moving away 30/04/2015 Slide 8 Static Electricity Slide 9 Practical 1 Blow a balloon up, tie end up. Rub balloon on jumper or top Stick to wall 30/04/2015 Slide 10 Practical 2 Rub plastic strips with various cloths See which one produces static electricity Try balloon and plastic strips near water 30/04/2015 Slide 11 Repel or attract 30/04/2015 1.Electrically charged objects can attract small objects 2.Two positively charged objects will repel 3.Two negatively charged objects will repel 4.A positively charged object and a negatively charged object will attract Slide 12 Like charges repel Slide 13 Slide 14 Opposite charges attract Slide 15 Static Electricity Slide 16 Practical 3 Van de Graaff 30/04/2015 Slide 17 Use and examples 30/04/2015 1.Static electricity can be used in photocopiers, smoke precipitator, and spray painting 2.A charged object can be discharged by connecting it to earth with a conductor 3.Static electricity can be dangerous (e.g. lightning). If the voltage becomes too great the negative charges can jump a gap causing a spark. This spark could ignite a flammable liquid nearby. Slide 18 Electrostatic Precipitator Electrostatic precipitator Slide 19 Static Electricity Static electricity Slide 20 Static Electricity Static electricity Slide 21 Quiz Quiz Slide 22 Lesson 2 Electricity Circuits Current Voltage Resistance 30/04/2015 Slide 23 Circuit Symbols Circuit symbols Slide 24 Switches - series circuit Switches series circuit Slide 25 Switches - parallel circuit Slide 26 Conduction in metals 30/04/2015 1.Metals are good conductors of electricity because they have delocalised electrons which can carry the current. Slide 27 Conduction in Metals Conduction in metals Slide 28 1.Ionic compounds conduct electricity when molten or dissolved in water. The current is carried by charged particles called ions. 2.The positive ions (cations) attract to the negative electrode (cathode) 3.The negative ions (anions) attract to the positive electrode (anode) 4.At the electrodes the ions can lose their charge and form new substances. 5.This process is called electrolysis Conduction in liquids Slide 29 Slide 30 Electric current 30/04/2015 1.Electric Current is the flow of charge 2.Current can be measured using an ammeter (connected in series) 3.Current is measured in Amps (A) 4.Increasing the Voltage will increase the current 5.Increasing the Resistance will decrease the current Slide 31 Current in a Series Circuit Slide 32 30/04/2015 Current in a series circuit If the current here is 2 amps The current here will be And the current here will be In other words, the current in a series circuit is THE SAME at any point Slide 33 30/04/2015 Current in a parallel circuit A PARALLEL circuit is one where the current has a choice of routes Here comes the current And the rest will go down here Half of the current will go down here (assuming the bulbs are the same) Slide 34 Current in circuits 1.In a series circuit the current is the same everywhere 2.In a parallel circuit the current divides on entering a junction and rejoins on returning to the battery 30/04/2015 Slide 35 Current in a Series Circuit Slide 36 Voltage or P.D 30/04/2015 1.Potential Difference is connected to the amount of energy that is gained or lost across part of a circuit 2.Potential Difference is measured using a Voltmeter (connected in parallel) 3.Potential Difference is measured in Volts (V) 4.Potential Difference gained across a cell or battery is called Voltage Slide 37 30/04/2015 Voltage in a series circuit V VV If the voltage across the battery is 6V and these bulbs are all identical what will the voltage across each bulb be? 2V Slide 38 30/04/2015 Voltage in a series circuit V V If the voltage across the battery is 6V what will the voltage across two bulbs be? 4V Slide 39 30/04/2015 Voltage in a parallel circuit If the voltage across the batteries is 4V What is the voltage here? And here? VV 4V Slide 40 P.D in circuits 1.In a series circuit the potential difference is shared between the components 2.In a parallel circuit the potential difference is the same across each component and equals the voltage across the battery 30/04/2015 Slide 41 Summary In a SERIES circuit: Current is THE SAME at any point Voltage SPLITS UP over each component In a PARALLEL circuit: Current SPLITS UP down each strand Voltage is THE SAME across eachstrand Slide 42 30/04/2015 An example question: V1V1 V2V2 6V 3A A1A1 A2A2 V3V3 A3A3 Slide 43 Answer voltage V1-3v V2-3v V3-3v current A1-1.5A A2-1.5A A3-3A 30/04/2015 Slide 44 Advantages of parallel circuits There are two main reasons why parallel circuits are used more commonly than series circuits: 1)Extra appliances (like bulbs) can be added without affecting the output of the others 2)If one appliance breaks it wont affect the others either Slide 45 30/04/2015 Georg Simon Ohm 1789-1854Resistance Resistance is anything that will RESIST a current. It is measured in Ohms, a unit named after me. The resistance of a component can be calculated using Ohms Law: Resistance = Voltage (in V) (in )Current (in A) V RI Slide 46 Resistance in circuits Series total resistance is equal to sum of all individual resistances (R=R 1 +R 2 ) Parallel-1/R = 1/R 1 +1/R 2 etc 30/04/2015 Slide 47 Calculate Q1. 1V, 1A calculate resistance Q2. Resistance =5 ohms, I = 2.5A V=? Q3.V=1.5V, Resistance=10ohms, I=? 30/04/2015 Slide 48 answers 1ohm 12.5V 0.15A 30/04/2015 Slide 49 Resistance Resistance Slide 50 Lesson 3 I-V graphs Conductors 30/04/2015 Slide 51 Series Circuit 1 bulb Slide 52 Series circuit 2 bulbs Series circuits 2 bulbs Slide 53 Parallel Circuit Slide 54 Ohmic conductors R is constant Provided temperature is constant, current is directly proportional to the potential difference across it. 30/04/2015 Slide 55 I-V for ohmic conductor 30/04/2015 Slide 56 Graphs 1.Current-Voltage graphs can be used to show how the current flowing through a component changes with different voltages 2.The current through a resistor is directly proportional to the voltage across the resistor (at a constant temperature) Slide 57 Comparing I-V graphs 30/04/2015 Slide 58 Slide 59 explanation 1.The resistance of a filament lamp increases as the filament gets hotter 2.A diode allows current to flow in one direction only (the diode has a very high resistance in the opposite direction) 3.The resistance of a light dependent resistor decreases with increasing light intensity 4.The resistance of a thermistor decreases with increasing temperature 30/04/2015 Slide 60 Resistance of Components Slide 61 Slide 62 Quiz Quiz