Electrical Energy & Capacitance

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Electrical Energy & Capacitance
2014-06-02 12:14:31
Chapter Eighteen
H Physics
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  1. electrical potential energy
    potential energy of an object due to its position relative to a source of electric force; results from the interaction of two objects' charges
  2. what happens when a charge moves because of an electric force
    work is done on the charge
  3. uniform electric field
    • field has the same value and direction at all points
    • parallel and evenly spaced field lines
  4. electrical potential energy and charge sign
    PE electric will increase if the charge is negative and decrease if the charge is positive
  5. single point charge, what happens; place another charge, what happens
    • single point charge produces a nonuniform electric field
    • second charge placed nearby creates a PE electric associated with the two charges
  6. PE electric and like/unlike charges
    positive for like charges, negative for unlike charges
  7. what happens to a small positive charge when you bring it closer to the large positive charge
    its energy increases and work is done on it
  8. what happens with charges in electric fields
    experiences a force and gains KE as it accelerates, and PE is lost
  9. when moved in the direction of an electric field, what happens to PE electric
    • for positive charges, lost
    • for negative charges, gained
  10. what type of force is electrostatic force
    conservative; path doesn't matter
  11. relationship between charge, potential difference, and current rate
    • charge is proportional to potential difference (both increase/decrease together)
    • increasing/decreasing these increases/decreases the current rate
  12. relationship between time constant and capacitator discharge rate
    • larger time constant means slower discharge rate
    • time constant RC describes the rate of charging and discharging
  13. electron hole
    • a missing electron in certain metals and semiconductors¬†
    • holes behave like positive charges, moving opposite to electrons under the effect of an electric field
  14. electrodes
    materials that make up the ends of the battery
  15. anode
    positively charged electrode; at the top of the battery
  16. cathode
    negatively charged electrode; at the bottom of the battery
  17. capacitance for a set of uncharged plates
    the amount of charge that can be stored is dependent on the area between the plates; capacitance is just a function of its geometric distributions
  18. why is it dangerous to touch the terminals of a high-voltage capacitator even after the potential difference has been removed? What can be done to make the capacitator safe to handle?
    • capacitator stores the energy, so even after the power leads are removed, it is charged; it could discharge through the body
    • discharge it before you handle it, ground it, or use an insulator
  19. difference between a capacitator and a battery
    • battery generates voltage via chemical reaction. Continues to provide power until all reagents are used up and reaction stops. No charge separation. Doesn't need an outside power force to operate.
    • capacitator has potentia because charge has been stored on it. When connected to circuit, current flows until charge has drained. Voltage is proportional to the amount of charge stored on it. Needs an outside power force to operate.
  20. charges that go in the same direction as electric field
    • electric field always goes away from positive
    • positive charge goes in same direction
    • PE decreases, KE increases, and work is done on the charge
  21. charges that go in the opposite direction of electric field
    • electric field always goes away from positive
    • negative charge goes in opposite direction
    • PE increases, KE decreases
  22. relationship between work and energy
    • when work is done on the object, it gains energy
    • when work is done by the object, it loses energy
  23. capitance
    • ability of a conductor to store energy in the form of electrically separated charges
    • a charged capacitator stores charge and energy to be used later
  24. capitance SI unit
    farads, C/V
  25. relationship btwn amount of charge you can  store, the plate area, and the space btwn plates
    • capitance is proportional to each plate area and inversely proportional to the distance btwn the plates
    • amount of charge you can store increases with bigger plate areas and less space btwn plates
  26. dielectric
    • insulating material that you can fill the space btwn plates with
    • increases capitance so more charge can be stored for a given potential difference
  27. electrical PE and capacitors
    charged capitators store PE because it requires work to move charges through a circuit to the opposite plates
  28. capacitators connected to power supply
    • when neutral there are equal amounts of positive and negative charges on the plates
    • power supply causes the charges to redistriute and separate, this separation creates EPE which can be used to do work
  29. how does a battery work
    • has reagents which due to their chemistry cause a redox reaction
    • electrons are separated and there is an electrostatic force
    • when in use the electrons travel through the circuit, already removed, and provide energy