Transcript Ohm`s Law
Ohm’s Law Ohm’s Law provides a basic understanding of how voltage, current, and resistance interact in a closed circuit. Assembled By Ken Mitchell Livermore TOPScience 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 – Source - 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 Control Variables Ohm's Law is a formulation of the of voltage, current, and resistance, expressed as: Where: V - is the Voltage measured in volts I - is the Current measured in amperes R - is the resistance measured in Ohms 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 Calculation Given: Voltage = 10 volts and the Resistance = 10 ohms How does the current, I, change as the resistance goes to zero? Place finger over I in the triangle, Voltage is over Resistance so we divide voltage by the resistance. Make small table: 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. 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