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Published byLeilani Jemmott Modified about 1 year ago

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Ohm’s Law Definition Whiteboards An Elaborate Analogy

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Ohm’s Law V = Voltage (like pressure) I = Current (like flow rate) +-+- A R R = V I R = Resistance in ohms ( ) V = Voltage in Volts (V) (pressure) I = Current in Amps (A) (flowrate) V

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Ohm’s Law - The way I think of it V = Voltage (like pressure) I = Current (like flowrate) R = Resistance to flow +-+- A R I = V R R = Resistance in ohms ( ) V = Voltage in Volts (V) (pressure) I = Current in Amps (A) (flowrate) V

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Ohm’s Law +-+- A R I = V R R = Resistance in ohms ( ) V = Voltage in Volts (V) (pressure) I = Current in Amps (A) (flowrate) V Demo - pass around resistors (two properties - power and resistance) Demo - power supply, resistor, light bulb (show increase/decrease V, and R) Black0 Brown1 Red 2 Orange3 Yellow4 Green5 Blue6 Violet7 Gray8 White9 Gold5% Silver10% No color20%

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Ohm’s Law +-+- A R= ?? R = V I R = Resistance in ohms ( ) V = Voltage in Volts (V) (pressure) I = Current in Amps (A) (flowrate) 12.0 V 120. mA Example 1: What is the resistance in the circuit above? R = V/I = (12.0 V)/(.120 A) = 100. Example 2: If there is a 220 resistor in the circuit above, what is the current? R = V/I, I = V/R = (12.0 V)/(220 ) = =.055 A or 55 mA

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Whiteboards 11 | 2 | 3 | 4 | 5 |

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What is the resistance of a light bulb if it draws 250 mA of current from a 6.15 V battery? (1000 mA = 1 A) 24.6 Given: R = V I R = ?? V = 6.15 V I =.250 A R = 24.6 W

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What current will flow if you plug a paperclip with a resistance of.065 into a 12 V source? 180 A Given: R = V I R =.065 V = 12 V I = ?? I = A W

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What voltage do you need to push 1.5 Amps of current through a 210 ohm resistor? 315 V Given: R = V I R = 210 V = ?? I = 1.5 A V = 315 V W

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What current flows through an 8.1 ohm speaker when there is a voltage of 3.45 V?.43 A Given: R = V I R = 8.1 V = 3.45 V I = ?? I = I =.43 A W

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An unknown resistor draws.0128 Amps of current from a 23.9 V source. What is the resistance? 1870 Given: R = V I R = ?? V = 23.9 V I =.0128 R = R = 1870 W

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A 1200 ohm resistor is hooked up to an unknown voltage source, and it draws 87.5 mA of current. What is the voltage? 105 V Given: R = V I R = 1200 V = ?? I =.0875 A V = 105 V W

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A 670 ohm resistor is connected to a 1.5 V battery. What time will it take for 3.0 C of charge to flow from the battery? 1340 s Given: R = V I I = q t t R = 670 V = 1.5 V I = ?? q = 3.0 C t = ?? t = 1340 s W

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A 3.0 V battery with a capacity of 350 mAh (350 milli amp hours) is drained in 4 hours and 27 minutes. What is the resistance of the circuit that it is attached to? 38 Given: R = V I I = q t t R = ?? V = 3.0 V I = ?? q = (.350e-3)(3600) = 1260 C t = 4* *60 = s R = = 38 W

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V3V3 A3A3 Symbols A Cell. + and -, Infinite current, R = 0, what’s really inside +-+- A Battery of cells A resistor A voltmeter, R = infinity An ammeter, R = 0

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An analogy Water in pipes:Electrons in wires: Flow rate (GPM)Current (Amps = C/s) PressureVoltage ConstrictionResistance Constant P PumpBatteries/Cells +-+- A3A3 R1R1 R2R2 Current convention Restriction Wires are superconductors

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