1 / 21

Electric Potential

Electric Potential. Chapter 17. Electric Potential Energy. Change in PE is important Work is done to move a charge from point a to point b Similar to gravitational PE Two parallel plates Electric field does work to move charge from a to b PE turns into KE, or PE = -Work.

percy
Télécharger la présentation

Electric Potential

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Electric Potential Chapter 17

  2. Electric Potential Energy • Change in PE is important • Work is done to move a charge from point a to point b • Similar to gravitational PE • Two parallel plates • Electric field does work to move charge from a to b • PE turns into KE, or PE = -Work

  3. Electric Potential • PE/unit charge • Va= PEa/q • Change in electric potential is important • Vba = Vb – Va = Wba/q • Unit – Volt = Joule/Coulomb • Positive charge moves high to low • Negative charge moves low to high • Ground

  4. Electric Potential Cont. • ΔPE = PEb – PEa = qVba • Potential difference is the measure of how much work a charge can do • Relationship to gravitation

  5. Example • An electron in a TV tube is accelerated from rest through a potential difference of Vba = +5000 V. • What is the change in potential energy of the electron? • What is the speed of the electron as a result of the acceleration? • Would the speed of a proton be more, less, or the same?

  6. Electric Potential and Electric Field • Parallel plates for an electric field • W = qVba • W = Fd = qEd • Vba = Ed • Units for electric field – V/m

  7. Example • Two parallel plates are charged to 50 V. If the separation between the plates is 0.050 m, what is the electric field between the two plates?

  8. Equipotential Lines • Potential is the same • No work is required to move along equipotential lines • Perpendicular to electric field lines • Conductor • No electric field exists inside conductor • Always the same potential

  9. Electron Volts • Unit of energy • Joule is too large • 1 eV = 1.6E-19 Joules • Must use joules if finding speed as was done before

  10. Electric Potential – Point Charge • V = kQ/r • Electric potential approaches zero as r approaches infinity

  11. Example • What is the minimum work required by some external force to bring a charge of 3 μC from an infinite distance away to a point 0.5 m from a charge of 20 μC?

  12. Electric Potential of Two or More Charges • Electric field = Vector • Use vector addition • Electric potential = Scalar • Add up numbers • Include positive and negative

  13. Example • The three charges shown are located at the vertices of an isosceles triangle. Calculate the electric potential at the midpoint of the base if each one of the charges at the corners has a magnitude of 5 nC. + 4.0 cm - - 2.0 cm

  14. Capacitance • Uses • Store charge • Block surges • Computer memory • Two plates separated by air or a dielectric • Depends on area and distance of separation

  15. Capacitance Cont. • Apply voltage to capacitor • Charge builds over time • Q = CV • C = Capacitance • Units are Coulombs/Volt = Farad • C is constant • Determined by area and distance, not by Q and V • C = Є0A/d

  16. Example • Calculate the capacitance of a capacitor whose plates are 20 cm x 3 cm separated by a 1 mm air gap. • Find the charge on each plate if it is connected to a 12 V battery. • What is the electric field between the plates?

  17. Dielectrics • Insulating sheet placed between plates of a capacitor • Can increase voltage applied to plates • Can reduce the space between the plates • Increases capacitance by a factor K • C = KЄ0A/d • What is happening on the molecular scale? • Computer keyboards

  18. Storage of Electrical Energy • Purpose is to move charge from one plate to another • Takes finite period of time and work • More charge = more work • Total work is equivalent to moving all the charge at once • W = QVf/2 • PE = ½ QV = ½ CV2 = ½ Q2/C

  19. Example • A camera flash stores energy in a 150 μF capacitor at 200 V. How much energy is stored?

  20. Summarizer Questions • Two parallel plates are uncharged. Does the set of plates have a capacitance? Explain. • Why is it dangerous to touch the terminals of a high-voltage capacitor even after the potential difference has been removed? What can be done to make the capacitor safe to handle?

  21. Capacitance Problem • You are asked to design a parallel-plate capacitor having a capacitance of 1.00 F and a plate separation of 1.00 mm. Calculate the required surface area of each plate. Is this a realistic size for a capacitor?

More Related