Ohm’s Law Definition Whiteboards An Elaborate Analogy

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

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

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

Ohm’s Law R = V I R = Resistance in ohms () + - A 120. mA 12.0 V R = V I R = Resistance in ohms () V = Voltage in Volts (V) (pressure) I = Current in Amps (A) (flowrate) 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 mA

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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) Given: R = V I R = ?? V = 6.15 V I = .250 A R = 24.6  W 24.6 

What current will flow if you plug a paperclip with a resistance of What current will flow if you plug a paperclip with a resistance of .065  into a 12 V source? Given: R = V I R = .065  V = 12 V I = ?? I = 184.6 A W 180 A

What voltage do you need to push 1 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 W 315 V

What current flows through an 8 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 W .43 A

An unknown resistor draws. 0128 Amps of current from a 23. 9 V source An unknown resistor draws .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  W 1870 

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

A 670 ohm resistor is connected to a 1. 5 V battery 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 W 1340 s

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? Given: R = V I I = q t R = ??  V = 3.0 V I = ?? q = (.350e-3)(3600) = 1260 C t = 4*3600 + 27*60 = 16020 s R = 38.14286  = 38  W 38 

A Cell. + and -, Infinite current, R = 0, what’s really inside Symbols + - A Cell. + and -, Infinite current, R = 0, what’s really inside A Battery of cells A resistor A voltmeter, R = infinity V3 An ammeter, R = 0 A3

Water in pipes: Electrons in wires: An analogy Water in pipes: Electrons in wires: Flow rate (GPM) Current (Amps = C/s) Pressure Voltage Constriction Resistance Constant P Pump Batteries/Cells Current convention Restriction Wires are superconductors R1 + - A3 R2