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Principles of Technology Waxahachie High School

Principles of Technology Waxahachie High School. Work in Electrical Systems PIC Chapter 2.3. PT TEKS. Work in Electrical Systems. Objectives: Explain the relationship between work done in electrical systems, charge moved, and the potential difference

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Principles of Technology Waxahachie High School

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  1. Principles of TechnologyWaxahachie High School Work in Electrical Systems PIC Chapter 2.3 PT TEKS

  2. Work in Electrical Systems Objectives: Explain the relationship between work done in electrical systems, charge moved, and the potential difference Calculate the amount of electrical charge in coulombs moving past a point in a circuit Define the units of electric current Solve electrical work problems, given voltage and charge information Identify the effects of work done in electrical systems Explain how efficiency relates to input work and output work in an electrical system

  3. Work in Electrical Systems A force does work on an object when it moves the object. A collection of charges creates an electric field. In an electrical system, when there is a difference between charges (positive and negative) a force is exerted and causes charges to move and does work.

  4. Work in Electrical Systems There must be an electrical voltage between two points within a field so that a force can be exerted on a charge placed in the field. If you connect the two points, the force causes the charge to move from one point to the other. The presence of voltageis what causes the charge to move and to do work. Batteries are a source of voltage.

  5. Work in Electrical Systems Electric charge is measure in coulombs (C). A single electron has a charge of 1.6 x 10 -19 C One Coulomb is equal to the charge of 6.25 billion billionelectrons.

  6. Work in Electrical Systems Electrical work = Change in Voltage x charge W = rV x q

  7. Work in Electrical Systems A battery is being charged. During the first 15 minutes of charging, 800 C of charge is deposited in the battery by an average potential difference (voltage) of 8 V. How much electrical work is done during the 15 minutes? W = rV x q W = 8 V x 800 C W = 6400 VC = 6400 Joules

  8. Work in Electrical Systems The rate at which charges flow is called electric current. Electric current in measured in coulombs/sec which is equal to an ampere. A device measuring an ampere is called an ammeter.

  9. Work in Electrical Systems Current = charge / change in time I = q/rt

  10. Work in Electrical Systems A 12 volt DC motor used a current of 4 amperes. Find the electrical work done to operate this motor for 2 minutes. q = I x Δt Minutes to seconds; 2 minutes = 120 sec q = 4 A x 120 sec q = 480 C W = ΔV x q W = 12 V x 480 C W = 5760 J

  11. Work in Electrical Systems List 4 things electrical work can do: Produce Movement Produce Thermal Energy Produce Light Produce Sound

  12. Work in Electrical Systems Produces Movement • Move fluids with pumps • Electric Cars • Electric fans

  13. Work in Electrical Systems Produces Thermal Energy • Electric Heaters • Clothes Dryers • Furnaces • Ovens • Blow Dryers

  14. Work in Electrical Systems Produces Light • Light bulbs • Laser

  15. Work in Electrical Systems Produces Sound • Radios • TV’s • CD players • Cell Phones

  16. Work in Electrical Systems In an electrical device, such as a motor, not ALL of the electrical work is converted to mechanical work. Instead, some of the electrical work is converted into thermal energy, thereby raising the temperature of the motor. The undesired thermal energy represents a loss of useful electrical work.

  17. Work in Electrical Systems This loss lowers the electrical efficiency of the system. Efficiency = output work / input work Percent Efficiency = output work / input work x 100

  18. Work in Electrical Systems The input work is 5760 Nm. The crane lifts the beam that weighs 2000 N to a height of 2.5 meters. What is the output work? What is the efficiency? What is the percent efficiency?

  19. Work in Electrical Systems Efficiency = output work / input work Output Work = Force x distance Output Work = 2000 N x 2.5 m Output Work = 5000 Nm Efficiency = 5000 Nm / 5760 Nm Efficiency = .87 % Efficiency = Efficiency x 100 % Efficiency = 87%

  20. Work in Electrical Systems Most electricity is produced at electrical generating stations by the following process: • Burningcoal, gas, or oil to produce heat • Heat converts water into steam • Steam turns a turbine • Turbine drives an electrical generator to produce electricity

  21. Work in Electrical Systems The overall efficiency of this process to produce electricity is 60%. Where do they lose the majority of their efficiency? Mechanical work to heat

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