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Ohm’s Law Definition Whiteboards An Elaborate Analogy.

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Presentation on theme: "Ohm’s Law Definition Whiteboards An Elaborate Analogy."— Presentation transcript:

1 Ohm’s Law Definition Whiteboards An Elaborate Analogy

2 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

3 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

4 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%

5 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

6 Whiteboards 11 | 2 | 3 | 4 | 5 |

7 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

8 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

9 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

10 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

11 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

12 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

13 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

14 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

15 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

16 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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