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Principles of Technology Waxahachie High School

Principles of Technology Waxahachie High School. Energy in Electrical Systems PIC Chapter 5.3. PT TEKS. Energy in Electrical Systems. Objectives : Describe a capacitor. Explain how a capacitor stores energy. Define capacitance. Calculate the electrical energy stored in a capacitor.

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Principles of Technology Waxahachie High School

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  1. Principles of TechnologyWaxahachie High School Energy in Electrical Systems PIC Chapter 5.3 PT TEKS

  2. Energy in Electrical Systems Objectives: Describe a capacitor. Explain how a capacitor stores energy. Define capacitance. Calculate the electrical energy stored in a capacitor. Describe an inductor. Explain how a conductor stores energy. Calculate the electrical energy stored in an inductor.

  3. Energy in Electrical Systems A capacitor is an electrical device that stores energy in an electric field. A power supply removes electrons from one plate in a capacitor and deposits them on a second plate.

  4. Energy in Electrical Systems This causes the plate that loses electrons to become positively charged and the plate that gains electrons to become negatively charged. The work done to create this electric field is equal to the potential energy stored in the field.

  5. Energy in Electrical Systems Equation for Potential Energy in an electric field = ½ x charge x Voltage W = ½ q V

  6. Energy in Electrical Systems If the charge is 10 C (coulombs) and the change in Voltage is 6 V, what is the work done? W = ½ q x V W = .5 x 10 x 6 W = 30 J

  7. Energy in Electrical Systems The charge on either plate of a capacitor is equal to the Capacitance x voltage Capacitors have fixed values of capacitance.

  8. Energy in Electrical Systems The symbol C is used to represent capacitance. Charge of a plate in a capacitor = Capacitance x voltage q = C x V The unit for capacitance is the farad (F). 1 farad = 1 coulomb per volt, or 1 F = 1 C/V

  9. Energy in Electrical Systems If the Capacitance is .0005 F (500 µF) and the Voltage is 200 V, what is the charge? q = C x V q = .0005 F x 200 V q = .1 C Most capacitors are measured in microfarads (µF) or picofarads (pF) 1 µF = 10-6 F 1pF = 10-12 F

  10. Energy in Electrical Systems Potential energy in a capacitor = ½ (Capacitance) (Voltage)2 PE = ½CV2

  11. Energy in Electrical Systems If the Capacitance is .0005 F and the Voltage is 200 V, what is the Potential Energy stored? PE = ½CV2 PE = .5 (.0005)(200)2 PE = .5 (.0005)(40,000) PE = 10 J

  12. Energy in Electrical Systems If an electric charge is moving, it will create a magnetic field.

  13. Energy in Electrical Systems Magnetic field lines with the electric current in the center:

  14. Energy in Electrical Systems If two currents are in the same direction, the wires are attracted.

  15. Energy in Electrical Systems If two currents are in opposite directions, the wires are repelled.

  16. Energy in Electrical Systems The Earth’s magnetic field is caused by currents in the molten iron core found at the center of the earth.

  17. Energy in Electrical Systems The Earth’s Magnetic Field causes the Northern Lights by attracting electrically charged particles given off by the sun.

  18. Energy in Electrical Systems A magnetic field can also create an electric field. This is called electromagnetic induction (EMF).

  19. Energy in Electrical Systems If a loop of wires moves through a magnetic field, a current is produced in the wire.

  20. Energy in Electrical Systems To increase the electricity created by a magnetic field: Use a larger magnet Use a coil (wire) with a larger diameter Use more turns of the wire Move the magnet faster

  21. Energy in Electrical Systems A capacitor stores energy in an electric field and an inductor is an electrical device that stores energy in a magnetic field.

  22. Energy in Electrical Systems The amount of energy that an inductor can hold is called inductance. Use the symbol L to represent Inductance and the unit is the Henry. Equation for EMF = -inductance (current/time) EMF = -L (I/t)

  23. Energy in Electrical Systems A coil with an inductance of .0045 Henrys and a current of 1000 amps for 2 seconds. What is the EMF? EMF = -L (I/t) EMF = -.0045 (1000/2) EMF = -.0045 (500) EMF = -2.25 V

  24. Energy in Electrical Systems Potential energy in inductors (Equation) = ½ inductance (current)2 PE = ½ L I2

  25. Energy in Electrical Systems A coil with an inductance of 8 Henrys and a current of 15 A has how much PE is stored? PE = ½ L I2 PE = ½ (8) 152 PE = ½ (8)(225) PE = 900 J

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