Ohms Law Definition Whiteboards An Elaborate Analogy Ohms

Ohm’s Law • Definition • Whiteboards • An Elaborate Analogy

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

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

Ohm’s Law I= + - V R R = Resistance in ohms ( ) V = Voltage in Volts (V) (pressure) I = Current in Amps (A) (flowrate) Demo - pass around resistors (two properties - power and resistance) Demo - power supply, resistor, light bulb (show increase/decrease V, and R) A V R Black Brown Red Orange Yellow Green Blue Violet Gray White Gold Silver No color 0 1 2 3 4 5 6 7 8 9 5% 10% 20%

Ohm’s Law + - 12. 0 V R=V I R = Resistance in ohms ( ) V = Voltage in Volts (V) (pressure) I = Current in Amps (A) (flowrate) A 120. m. A R= ? ? 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 ) =. 05454 =. 055 A or 55 m. A

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What is the resistance of a light bulb if it draws 250 m. A of current from a 6. 15 V battery? (1000 m. A = 1 A) Given: R=V I R = ? ? V = 6. 15 V I =. 250 A R = 24. 6

What current will flow if you plug a paperclip with a resistance of 0. 065 into a 12 V source? Given: R=V I R =. 065 V = 12 V I = ? ? I = 184. 6 A 180 A

What voltage do you need to push 1. 5 Amps of current through a 210 ohm resistor? Given: R=V I R = 210 V = ? ? I = 1. 5 A V = 315 V

What current flows through an 8. 1 ohm speaker when there is a voltage of 3. 45 V? Given: R=V I R = 8. 1 V = 3. 45 V I = ? ? I = 0. 425925926 I =. 43 A

An unknown resistor draws 0. 0128 Amps of current from a 23. 9 V source. What is the resistance? Given: R=V I R = ? ? V = 23. 9 V I =. 0128 R = 1867. 1875 R = 1870

A 1200 ohm resistor is hooked up to an unknown voltage source, and it draws 87. 5 m. A of current. What is the voltage? Given: R=V I R = 1200 V = ? ? I =. 0875 A V = 105 V

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? Given: R=V I I = q t R = 670 V = 1. 5 V I = ? ? q = 3. 0 C t = ? ? t = 1340 s

A 3. 0 V battery with a capacity of 350 m. Ah (350 milli amp hours) is drained in 4 hours and 27 minutes. What is the resistance of the circuit that it is attached to? Given: R=V I I = q t R = ? ? V = 3. 0 V I = ? ? q = (. 350 e-3)(3600) = 1260 C t = 4*3600 + 27*60 = 16020 s R = 38. 14286 = 38

Symbols + - A Cell. + and -, Infinite current, R = 0, what’s really inside A Battery of cells A resistor V 3 A voltmeter, R = infinity A 3 An ammeter, R = 0

An analogy Water in pipes: Flow rate (GPM) Pressure Constriction Constant P Pump + - Electrons in wires: Current (Amps = C/s) Voltage Resistance Batteries/Cells R 1 A 3 R 2 Current convention Restriction Wires are superconductors