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Chapter 4

Chapter 4. Energy. Objectives. Define work, power, and horsepower. Calculate electrical power in watts. Convert horsepower to watts. Combine Ohm’s law with Watt’s law to find unknown currents, voltages, resistances, and powers. Objectives. Read a wattmeter. Determine efficiency.

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Chapter 4

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  1. Chapter 4 Energy

  2. Objectives • Define work, power, and horsepower. • Calculate electrical power in watts. • Convert horsepower to watts. • Combine Ohm’s law with Watt’s law to find unknown currents, voltages, resistances, and powers. Permission granted to reproduce for educational use only.

  3. Objectives • Read a wattmeter. • Determine efficiency. • Determine gear and pulley ratios and power. • State and explain Ohm’s law. Permission granted to reproduce for educational use only.

  4. Work • Expressed in foot-pounds or inch-pounds • Work = F× D • F = force in pounds • D = distance in feet Permission granted to reproduce for educational use only.

  5. Power (P) • Time rate of doing work Permission granted to reproduce for educational use only.

  6. Units of Power • Unit of mechanical power is horsepower (hp) • Unit of electrical power is watt (W) • P = E× I • P = watts • E = volts • I = amperes • 746 watts = 1 horsepower Permission granted to reproduce for educational use only.

  7. Watt’s Law • P = I× E Permission granted to reproduce for educational use only.

  8. Review What is force applied over a distance called? Work Permission granted to reproduce for educational use only.

  9. Review What is power? The amount of work done based on a time period Permission granted to reproduce for educational use only.

  10. Review What is the unit of electrical power? Watt (W) Permission granted to reproduce for educational use only.

  11. Review What is the power formula also called? Watt’s law Permission granted to reproduce for educational use only.

  12. Ohm’s Law and Watt’s Law Permission granted to reproduce for educational use only.

  13. Ohm’s Law and Watt’s Law (Cont.) • Combination of two laws will let you solve for voltage, current, resistance, or power Permission granted to reproduce for educational use only.

  14. Wattmeters • Measure instantaneous power with an electrodynamometer movement Permission granted to reproduce for educational use only.

  15. Watt-Hours • Watt-hour meters read in kilowatt-hours (kWh) Permission granted to reproduce for educational use only.

  16. Watt-Hours (Cont.) • 4255 kWh Permission granted to reproduce for educational use only.

  17. Watt-Hours (Cont.) • 3970 kWh Permission granted to reproduce for educational use only.

  18. Review What is the D’Arsonval movement equivalent for measuring power? Electrodynamometer movement Permission granted to reproduce for educational use only.

  19. Review What is a meter that measures instantaneous power? Wattmeter Permission granted to reproduce for educational use only.

  20. Efficiency • Input power versus output power Permission granted to reproduce for educational use only.

  21. Energy Efficiency Rating (EER) • Government checked • Expressed as percentage • Higher percentage = higher efficiency • Higher efficiency = less costly to operate Permission granted to reproduce for educational use only.

  22. Gears, Pulleys, and Power • Law of conservation of energy Permission granted to reproduce for educational use only.

  23. Gears, Pulleys, and Power (Cont.) Permission granted to reproduce for educational use only.

  24. Review What is efficiency? The ratio of input power to output power Permission granted to reproduce for educational use only.

  25. Review What is an energy efficiency rating? A rating of electrical equipment, expressed as a percentage Permission granted to reproduce for educational use only.

  26. For Discussion • What is the relationship between Ohm’s law and Watt’s law? • What are some of the ways you can conserve energy in your everyday life? Permission granted to reproduce for educational use only.

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