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Ohm’s Law

Ohm’s Law. Mr. Brudelie. Ampere (A). Named for Andre Ampere Ampere is a measurement of electricity flowing through a circuit (gallons/min). Electron Flow Theory States that since electrons are negative, current flows from the most negative point in the circuit to the most positive

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Ohm’s Law

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  1. Ohm’s Law Mr. Brudelie

  2. Ampere (A) • Named for Andre Ampere • Ampere is a measurement of electricity flowing through a circuit (gallons/min)

  3. Electron Flow Theory • States that since electrons are negative, current flows from the most negative point in the circuit to the most positive (- terminal hot) • Conventional Current Flow Theory • Flows from positive to negative, + terminal hot (car battery)

  4. 1 electron moves at a rate of 3 inches/hr • A complete path must exist before current can flow through a circuit • Often called a closed circuit • Short circuit happens when a path is math back to the power source that doesn’t have a load (resistor) • Leads to blown fuses, tripped breakers, melted wires, fires

  5. Ground Conductor • Provides a return path and completes the circuit • Only becomes used when a circuit fault develops • Prevents shocks if the hot wire contacts the appliance frame

  6. Volt • Voltage is the potential difference b/w 2 pts of a wire carrying 1 amp dissipated at 1 watt • The force that pushes electrons through a wire (electrical pressure) • Voltage CANNOT flow • The potential to do something • Common wall outlet, 120V, has no flow until something is plugged into it to complete the circuit

  7. Ohm • An Ohm is the unit of resistance to current flow • Named after Georg S. Ohm • Uses Greek letter omega • Letter R, stands for resistance represents ohms in a formula

  8. An ohm is the amount of resistance that allows 1 amp of current to flow when the voltage is 1 V • Without resistance every circuit would be a short circuit • The higher the resistance the higher the hindrance to current flow • Anytime current flows through a resistance, heat is produced

  9. Watt • Measure of the amount of power being used in a circuit • Names after English scientist, James Watt • Represented by W, in equations used as P • Proportional to the amount of force and flow • 120 V with current of 1 A =? W • 120 W

  10. 240 V with a current of 1 A =? W • 240 W! • 120 V with a current of 2 A =? W • 240 W

  11. Horsepower • Watt compared to sell his steam engines in terms people could understand • The average horse working at a steady pace could do 550 foot-pounds or work/sec • Ft-lb is the force required to raise 1lb 1ft • 1 hp = 550 ft-lb/s • 1 hp = 746 W

  12. The joule is the SI equivalent to the watt • Joule is 1 newton-meter • 1 joule = 1 watt-s • Example: • An elevator must lift a load of 4000lbs to a height of 50ft in 20sec. How must horsepower needed?

  13. 4000 lb X 50 ft = 200,000 ft-lb • 200,000 ft-lb/20 sec = 10,000 ft-lb/s • 10,000 ft-lb/s / 550 ft-lb/s = 18.18 hp

  14. Ohm’s Law • Takes 1 V to push 1 A through 1 ohm • E = I X R • I = E/R • R = E/I • E = Voltage (V) • I = amperage (A) • R = Resistance (ohms)

  15. Metric Prefixes • Deka = 10 • Hecto = 100 • Kilo = 1000 • Deci = 1/10th • Centi = 1/100th • Milli = 1/1000th

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