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Ohm’s Law provides a basic understanding of how voltage, current, and resistance interact in a closed circuit. Water Tank Sprinkler On-Off Valve Water Analogy to Electrical Circuit Guess where the return circuit is. Replaces water flow in pipe Electron Flow Replaces the sprinkler Replaces the water tank L O A D Battery Switch Replaces on-off water valve See notes below Simple Electrical Circuit Equivalent to the Water System Voltage – The electromotive force (EMF) or potential difference between two points in a circuitSource - DC – Batteries (dry cells, Lead Acid, LiH, etc.) Expressed in “Volts.” Physical example – The depth of water in a water tank. Current – Electron flow in the circuit, from + to – side of the power source (battery). Expressed in Amperes. Physical example – Water flowing through a hose. Resistance -- An electrical component that operates on voltage applied across it. Because it does work and dissipates the energy as heat it’s simply called a “Load” and is expressed in “ohms.” Physical example – The lawn sprinkler. The Three Variables Ohm's Law is a formulation of the of voltage, current, and resistance, expressed as: V=IxR Where: V - is the Voltage measured in volts (V) I - is the Current measured in amperes (amps) R - is the resistance measured in Ohms (Ω) Therefore: Volts = Amps times Resistance Ohm’s Law Simplified The Variables: Divide across here V V = Voltage Multiply across here I = Current R = Resistance I R Solution: Cover the unknown variable and the remainder gives the solution. How to find the Unknown Variable Using Ohm’s Triangle V I R Example: What happens to current (I) as the resistance (R) goes to zero? Hold a finger over current (I) and observe what happens when the resistance (R) goes to zero. ******** Current (I) becomes infinite (actually it will be limited by the internal resistance of the voltage source). An Example Using Ohm’s Triangle Example Calculations If Voltage = 10 volts and the Resistance starts at 10 ohms How does the current, I, change as the resistance goes to zero? According to Ohm’s Law we divide voltage by the resistance Voltage / Resistance = Current (I) 10 volts / 10 ohms = 1 amp 10 volts / 5 ohms = 10 volts / 2 ohms = 5 amps 10 volts / 1 ohm = 10 amps 10 volts / ½ ohms = 20 amps 10 volts / zero ohms = Unlimited amps* 2 amps *Current is actually limited by the battery’s internal resistance (impedance). Ohms' Law Example Current in Amps 25 20 Voltage 15 Resistance 10 Current 5 0 1 2 3 4 5 6 7 8 9 10 11 Resistance in Ohms