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Download Science 9 electricity powerpoint Topic 2
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Unit D Section 2.0 Technologies can be used to transfer and control electricity 2.1 – Controlling the Flow of Electrical Current • Electrical current flows through circuits • The amount of current that can flow through a circuit is limited by the conductive properties of the components in the circuit http://videos.howstuffworks.com/discovery/ 27710-how-do-they-do-it-creating-neonsigns-video.htm Conductors and Insulators • In conductors, electrons can move easily because they are not tightly bound to the nuclei of the atoms • In insulators, the electrons cannot move easily • http://www.youtube.com/watch?v=8Pnsbh0DrE 4 Superconductors • A superconductor is a material that have no resistance to electron flow • Many materials are superconductive at very low temperatures http://app.discoveryeducation.ca/search?Ntt=sup erconductors Using Conductors, Resistors & Insulators • Resistance is a measure of how difficult it is for electrons to flow • Resistance is measured in ohms (Ω) • Resistors are parts of a circuit that provide high resistance to reduce the amount of current flowing through the circuit • For any given voltage, more current flows through a resistor with a LOW resistance than one through with a HIGH resistance • http://www.bbc.co.uk/bitesize/standard/physics/ using_electricity/resistance/activity/ Devices that use Resistors • The more resistance a substance has, the more the substance gains energy from each electron passing through it. • The energy gained is radiated to its surroundings as either heat or light • Some examples of devices that use resistors are: • http://www.youtube.com/watch?v=t4SP_mYh4 wQ • HowStuffWorks How does a lie detector (polygraph) work Switches and Variable Resistors • Switches create a break in the circuit that interrupts current flow, therefore controlling the flow of current in the circuit • A variable resistor is another type of control • These resistors (also known a rheostats) allow you to adjust the amount of current flowing through a circuit, rather than simply turning it on or off • This can be done through control knobs or pedals Topic 2.2 Modeling and Measuring Electricity Electrical Charge • Electrical charge is measured in Coulombs • This is named after Charles A. Coulomb • 1 coloumb = 6.25 billion billion electrons 2.2 – Modeling and Measuring Electricity • Voltage is a measure of how much potential energy each electron that flows through a circuit possesses • Voltage is related to both current and resistance in circuits Ohm’s Law • In 1826, Georg Ohm determined through experiments that voltage (V), current (I) and resistance (R) are mathematically related: • Resistance is measured in ohms (Ω) V IR Ohm’s Law states that, as long as temperature remains constant: 1. The resistance of a conductor remains constant 2. The current is directly proportional to the voltage applied • http://www.youtube.com/watch?v=mHLvtGjum4 • MAKE presents: Ohm's Law Applying Ohm’s Law 2.3 – Analyzing and Building Circuits • Circuit diagrams or schematics are representations of a circuit that is built • Recall that all circuits require four components: Parallel and Series Circuits • Circuits can be divided into two general types: parallel and series • These circuit types are defined by the number of branches that are present in the circuit • http://www.bbc.co.uk/schools/gcsebitesize/scie nce/add_aqa/electricity/circuitsact.shtml Series Circuits • Definition: • Diagram: the current passes through each bulb in turn – there is only one pathway Parallel Circuits • Definition: • Diagram have a separate path for each section of the circuit Effects of Multiple Paths in Parallel Circuits • In parallel circuits, adding more resistors in circuits actually will reduce the overall resistance of the circuit • As well, the voltage change in each branch is equal Applications of Parallel and Series Circuits • Parallel circuits are more commonly used in devices than series circuits • Imagine what would occur if your house used series circuits instead of a number of parallel circuits… Transistors • In tiny consumer electronics, transistors are used instead of conventional switches • Transistors are made of three layers of silicon sandwiched together • These transistors have no moving parts and operate on digital code running through the middle layer of the transistor to control the movement of current through a circuit Microcircuits • Are also called integrated circuits • Are made up of microscopic transistors and resistors • It is a circuit on an extremely small scale