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Resistance Factors Equation (Ohm’s Law) Interpreting graphs Circuits and Resistance

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Here’s the deal electrons move through a conductor. electrons can collide with the atoms of the conductor. This makes it more difficult for the current to flow.

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Like a marathon… The roughness, difficulty and width of the road, including the obstacles along the way are some resistances to their forward motion.

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Length of wire As length increases, resistance increases Diameter of wire As diameter increases, resistance decreases Temperature As temperature increases, resistance increases So, in a conducting material, what factors affect the flow of electrons?

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Resistance Measure of how a material or object opposes the flow of current Ratio of pd across resistor and current in the resistor

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Energy and Power V = energy per unit charge I = charge per unit time Energy = VIt Unit: Joules, J Power = energy per unit time Power = VI Unit : Watts, W

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Ohm’s Law Volt(s) Ampere(s) Ohm(s)

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Experiment 1

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Gradient is constant Gradient = I/V = constant value Resistance = 1/Gradient = constant value Fixed Resistance Fixed Resistor What does the graph mean?

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Experiment 2

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Gradient is changing decreasing Gradient = I/V = decreasing value Resistance = 1/Gradient = increasing value Increasing Resistance Filament bulb increases in temperature What does the graph mean?

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Interpreting Graphs What is the resistance when V=1 and V=3?

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Interpreting Graphs What is the resistance when V=2, 5 and 5.5 volts?

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Series Circuit I total = I 1 = I 2 = I n V total = V 1 + V 2 + V n R total = R 1 + R 2 + R n

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Parallel Circuit I total = I 1 + I 2 + I n V total = V 1 = V 2 = V n = ++ RnRn R2R2 R1R1 1 11 R total 1

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Series The total resistance increases The total current decreases Parallel The total resistance decreases The total current increases What happens to the current in the circuit when you add more resistors?

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Series More bulbs divide energy between themselves Brightness decreases Parallel Voltage or energy across each bulb is the same Brightness is unaffected What happens to the brightness of the bulbs when more are added?

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Series There is only one path for current Since bulb is busted, there is an open in the circuit Other bulbs don’t light Parallel The path for each bulb is independent Other bulbs are lit; only busted bulb is unlit What happens to the other bulbs in the circuit when one of the bulbs is busted?

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