Circuits • Lesson 01: Charge • Lesson 02: Circuit Diagrams • Lesson 03: Series Circuits • Lesson 04: Parallel Circuits Which Circuit? • Lesson 05: Resistance • Lesson 06: Voltage, Current and Resistance • Lesson 07: Voltage, Current and Resistance • Lesson 08: Revision
Glossary • ammeter – A device used to measure current. • ampere – The unit used to measure current. Its symbol is A. • battery – The scientific word for two or more cells that are joined together. • cell – A chemical source of voltage. The chemicals inside this device react and electrons are pushed out into the circuit. • circuit – A complete path that current can travel along. • current– The rate of flow of electric charge in a circuit. It is measured in amperes (A). • electron flow – The movement of negatively-charged electrons from a negative terminal around a circuit. • parallel circuit – A complete circuit that branches into two or more paths. • potential difference – The scientific name for voltage, measured in volts (V). Measured across a component, it is the difference in electrical potential energy between the two sides of the component. • series circuit – A complete circuit in which components are wired one after the other in a continuous loop. • volt – The unit used to measure potential difference (voltage). Its symbol is V. • voltmeter – A device used to measure potential difference (voltage). • voltage – Another name for potential difference. For a cell, it is the amount of energy that the cell gives to each electron pushed out into the circuit. • diode – A component that allows current to flow in one direction only. • light dependent resistor – A component whose resistance changes in response to light intensity. • ohm – The unit of electrical resistance, named afterGeorg Ohm. • Ohm’s law – Formula used to relate current, voltage and resistance, if the temperature remains constant. R = V/I. • resistance – The opposition to the flow of charge. • resistor – A component that opposes the flow of charge. • thermistor – A component whose resistance changes in response to temperature. • variable resistor – A component whose resistance can be adjusted to vary the amount of current.
Double Award Syllabus: • explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting (P2.10) • understand that the current in a series circuit depends on the applied voltage and the number and nature of other components (P2.11) • describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how this can be investigated experimentally (P2.12) • describe the qualitative effect of changing resistance on the current in a circuit (P2.13) • describe the qualitative variation of resistance of LDRs with illumination and of thermistors with temperature (P2.14) • recall and use the relationship between voltage, current and resistance: • voltage = current × resistance V = I × R (P2.15) • understand that current is the rate of flow of charge (P2.16) • recall and use the relationship between charge, current and time: charge = current × time Q = I × t (P2.17) • recall that electric current in solid metallic conductors is a flow of negatively charged electrons (P2.18).
Separate Science Syllabus Energy and Potential Difference in Circuits • explain why a series or parallel circuit is more appropriate for particular applications, including domestic lighting • understand that the current in a series circuit depends on the applied voltage and the number and nature of other components • describe how current varies with voltage in wires, resistors, metal filament lamps and diodes, and how this can be investigated experimentally • describe the qualitative effect of changing resistance on the current in a circuit • describe the qualitative variation of resistance of LDRs with illumination and of thermistors with temperature • recall and use the relationship between voltage, current and resistance: • voltage = current × resistance • V = I × R • understand that current is the rate of flow of charge • recall and use the relationship between charge, current and time : • charge = current × time • Q = I × t • recall that electric current in solid metallic conductors is a flow of negatively charged electrons • recall that: • voltage is the energy transferred per unit charge passed • the volt is a joule per coulomb Electric charge • identify materials which are electrical conductors or insulators, including metals and plastics • recall that insulating materials can be charged by friction • explain that positive and negative electrostatic charges are produced on materials by the loss and gain of electrons • recall that there are forces of attraction between unlike charges and forces of repulsion between like charges • explain electrostatic phenomena in terms of the movement of electrons • recall the potential dangers of electrostatic charges, e.g. when fuelling aircraft and tankers • recall some uses of electrostatic charges, e.g. in photocopiers and inkjet printers
Charge22/09/2014 Aim: • To generate a charge • To calculate charge Starter: • Where is the static electricity in the picture?
How is Static Charge Generated? • How can you generate static charge? Around the outside of an atom are electrons, which have a negative charge. The nucleus at the centre of an atom contains protons, which have a positive charge.
Charging materials Video
Investigating pairs of charges Separate Science
Charge Separate Science • Insulators can be charged by friction • If a material is turned positive then electrons have been lost • if the material becomes negative the electrons have been gained • Like charges repel • Different charges attract
Demos • Water • Paper
Charge • The number of electrons (or other ions) • Symbol: Q • Units: coulomb (C) • Charge on 1 electron = 1.6 × 10-19 C Charge =currentxtime (in C) (in A) (in s) Q u I t Charles–Augustin de Coulomb (1736-1806) Q I t
Example questions • A circuit is switched on for 30s with a current of 3A. How much charge flowed? • During electrolysis 6A was passed through some copper chloride and a charge of 1200C flowed. How long was the experiment on for? • A bed lamp is switched on for 10 minutes. It works on a current of 0.5A. How much charge flowed?
How are planes refuelled safely? Separate Science A build up of static charge when refuelling a plane could cause an explosion. This can be prevented by joining the delivery tanker and the fuel tank electrically with a metal wire. The wire provides a path for electricity to flow along, and so prevents the build up of any potentially dangerous static charge. metal wire Petrol Pump
Dangers Separate Science • Sparks are caused by electrons moving • When a plane is refuelling you can get a build up of electrostatic charges
How does a photocopier work? Separate Science
What happens in a photocopier? Separate Science
Inkjet printer Separate Science A4 paper Positive plate Fine nozzle Negative plate • The ink droplets are charged as they thrust against the nozzle • The droplets are deflected as they pass between two electrically charged plates • The amount of charge, i.e. the size and direction of the voltage, on the plates keeps changing to drive each droplet to the right place on your paper • What charge will the droplets deflected upwardly have? Why? • They will be negatively charged, because -ve charges are attracted by the positive plate at the top and repelled by the negative plate at the bottom.
How does spray painting cars work? Separate Science
How does static charge reduce pollution? Separate Science A precipitator in the chimney of a power station uses static electricity to filter smoke particles from waste gases. positively- charged metal plates The smoke particles pass through a charged grid and pick up a negative charge. They are then attracted to the positively-charged collecting plates. smoke particles The smoke particles lose their charge and fall back down the chimney, so the waste gases emitted are free of polluting smoke. metal grid at a high voltage
Uses Separate Science • Electrostatic charges are used in photocopiers, inkjet printers, spray paints and precipitators
Static electricity – useful or a problem? Separate Science
‘Van de Graaff’ generator Brainiac
Chargerecap Aim • To generate a charge • To calculate charge
Circuit Diagrams22/09/2014 Aim • Use circuit symbols • Understand circuit diagrams Starter: True or False(back of books) Voltage can also be called potential difference. There must be a gap in a circuit for a current to flow. Electrons carry energy round a circuit. A light bulb transfers electrical energy into heat and light. Current is measured in volts. If more electrons start flowing round a circuit the current gets smaller
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Circuit Symbols Wire Connected Wire Non connecting wire Cell Battery Power supply Switch Voltmeter Ammeter Motor Fuse Buzzer Diode Bulb Resistor Thermistor Variable Resistor Light Dependant Resistor (LDR)
- - - - - - - - - - - - - - - - If there is only one path for the current we say the bulbs are connected in SERIES.
- - - - - - - - - - - - - - - - Here the current has two routes. Any circuit with more than one route means that the bulbs are connected in PARALLEL.
- - - - - - - - - - - - - - - - If a wire is connected around the bulb all the current will bypass the bulb and it goes out - - - - We call this a SHORT CIRCUIT
Building Circuits Practise • 1 Power Pack set at 3V 2 Bulbs • 1 Switch 1 Motor • 1 Buzzer 6 Wires • 1 Voltmeter 2 Croc Clips • Draw each circuit first • When Connecting Parallel circuits connect up the series section first. • make sure you have that right. • then add at the parallel branch. • Make sure they connect where the “blobs” are in the circuit. • Measure the Voltage across each component and the power pack and note it down on your circuit diagram • The buzzers need to be connected the correct way
2 3 1 M M 4 5 6 M
Circuit Diagramsrecap Aim Use circuit symbols Understand circuit diagrams Homework
Series Circuits22/09/2014 • Aims: • To define Current, Voltage and Resistance • To investigate current and voltage in series circuits Quiz: Quiz: Power supply Voltmeter Diode Thermistor Light Dependant Resistor (LDR) Battery Power supply Switch Voltmeter Ammeter Diode Resistor Thermistor Variable Resistor Light Dependant Resistor (LDR)
Potential Difference • The push on electrons in a circuit. • so bigger push, faster electrons, more current, brighter bulb • Symbol: V • Units: volts (V) • A.k.a. Voltage Alessandro Giuseppe Antonio Anastasio Volta (1745-1827)
Current • The number of electrons flowing past a point in a circuit. • So faster electrons or more electrons, bigger current, brighter bulb • Conventional Current flows from positive to negative however electrons are negative so they really flow from negative to positive • Symbol: I • Units: ampere (A) (ampere = amps) André-Marie Ampère (1775-1836)
Resistance • How hard it is for a current to flow through a material. • So bigger resistance but same voltage gives a smaller current • Symbol: R • Units: ohms (Ω) George Simon Ohm(1789-1854)
Analogy 1: Cross Country Run • Copy down the sketch on the board and annotate it. • USE MOST OF A PAGE LEAVE SPACE FOR FURTHER ADDITIONS NEXT LESSON • PE Teachers = Voltage • Pupils = electrons • Rate of pupils moving = Current • Other Teachers counting Pupils = Ammeter • Obstacles = Resistances (e.g. Resistors, bulbs, motors ...) • Short cuts = Short circuits
Experiment • Follow the experiment sheet • DO NOT WRITE ON THE SHEET
Series circuits – experiment NOTE: Voltage Reading on 3 bulbs, 1 battery is wrong should be 0.67 V