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Transcript
Additional Physics – Forces Exam Date - Potential difference – current graph L/O :- To be able to recognise potential difference – current graphs Potential difference – current graph L/O :- To be able to recognise potential difference – current graphs Answers in the back of your books 1.How can you work out resistance in a circuit? 2.What affects the resistance in a wire? 3.What is the equation for working out current? 4.Does current split down branches of a parallel circuit? 5.Does voltage split down branches of a parallel circuit? Potential difference – current graph L/O :- To be able to recognise potential difference – current graphs True or false: 1. The shorter the wire the lower the resistance. 2. The thicker the wire the lower the resistance. 3. The material of the wire can affect the resistance in the wire. 4. The hotter the wire the higher the resistance. 5. The straighter the wire the lower the resistance. Quick quiz 1. 2. 3. 4. 5. What 2 factors affects your momentum? How can you work out resistance in a circuit? What affects the resistance in a circuit? What is acceleration measured in? What is the equation for work done and what is it measured in? 6. What is the equation for working out current? 7. Name 3 things which can affect stopping distance Time limit 5 minutes Graph paper • Plot the results of your resistance experiment. Resistance in different materials Vid clip Ohm’s law Ohm’s Law The current through a resistor at constant temperature is directly proportional to the potential difference across the resistor In other words; The current goes up at a constant rate with the voltage {only under same temperature} Resistance and Ohms Law Video clip Current (A) 0 Current (A) Potential Difference (V) 0 You will need to be able to recognise this graph! 0.25 0.05 0.1 0.15 0.2 0.25 0.5 1 1.5 2 2.5 This resistor supports Ohm’s Law. What does this graph tell you about the relationship between potential difference and voltage in a resistor at a constant temperature? 0.2 0.15 0.05 0 0.5 1 1.5 2 2.5 Potential Difference (V) REMEMBER - Ohm’s Law The current through a resistor at constant temperature is directly proportional to the potential difference across the resistor What do these graphs tell you about each component? Filament Bulb Diode Get in pairs and write down what you can tell from each graph? What do these graphs tell you about each component? Filament Bulb Diode REMEMBER – The flatter the graph the higher the resistance What do these graphs tell you about each component? Filament Bulb The filament bulb follows ohms law at low temperatures. At higher currents the temperature increases, so it doesn’t follow Ohms law. Diode The diode has a high resistance in one direction. So it resists the flow of electrons in that direction. REMEMBER – you must be able to recognise these graphs • Diodes are electronic components that can be used to regulate the potential difference in circuits • Light-emitting diodes (LEDs) give off light and are often used for indicator lights in electrical equipment The diode has a very high resistance in one direction – this means that current can only flow in one direction • The filament lamp is a common type of light bulb (it contains a thin coil of wire called the filament) • The filament heats up when an electric current passes through it, and produces light as a result The filament lamp does not follow Ohm’s Law – its resistance increases as the temperature of its filament increases. As voltage increases the bulb gets hotter, and its resistance increases What have you learnt? • What do these graphs represent?