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Regents Physics

Regents Physics. Electric Fields. Electric field. The region around a charged particle through which a force is exerted on another charged particle. Electric Field Line. The imaginary line along which a positive test charge would move in an electric field.

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Regents Physics

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  1. Regents Physics Electric Fields

  2. Electric field • The region around a charged particle through which a force is exerted on another charged particle.

  3. Electric Field Line • The imaginary line along which a positive test charge would move in an electric field

  4. The direction of an electric field is the direction of the force on a stationary positive test charge located at any point on a field line.

  5. On a curved field line, the direction of the field at any point is the tangent drawn to the field line at that point. • Electric field lines begin on positive charges (or at infinity) and end on negative charges (or infinity).

  6. Field lines NEVER intersect.

  7. Electric field strength • The force on a stationary positive test charge per unit charge in an electric field. E = Fe/q Fe=electrostatic force in newtons q=charge in coulombs E=electric field strength in newtons per coulomb VECTOR quantity!!!

  8. Ex. • What is the magnitude of the electric field strength at a point in a field where an electron experiences a 1.0-newton force?

  9. Ex. • What is the magnitude of the electric field strength at a point in a field where an electron experiences a 1.0-newton force? • Use E = Fe/q. • Fe=1.0N • Q=1.60 x 10^-19C

  10. Ex. • What is the magnitude of the electric field strength at a point in a field where an electron experiences a 1.0-newton force? • Use E = Fe/q. • Fe=1.0N • Q=1.60 x 10^-19C = 6.3 x 10^18 N/C

  11. Field Around a Point Charge or Sphere • Field lines extend radially outward from a positive point charge and radially inward from a negative point charge. • On a sphere, charge is distributed uniformly, and electric field lines are perpendicular to the surface.

  12. Sphere… • Electric field strength within a hollow, charged, conducting sphere is zero.

  13. Field between two oppositely charged parallel plates • If d between two is relatively small compared to area, electric field is uniform. • Parallel to each other. • Electric field strength is same at every point between plates.

  14. Field between two oppositely charged parallel plates • Magnitude of electric force on an electron or a proton located at any point between two given oppositely charged parallel plates is the same. • Particle speed increases as it approaches plates of opposite sign.

  15. Potential Difference • The work done (or change in potential energy) per unit charge as a charged particle is moved between two points in an electric field. V= W/q Unit= joule/coulomb = volt

  16. 11/7/2008

  17. volt • Derived SI unit for potential difference

  18. If an elementary charge is moved against an electric field through a potential difference of one volt, the work done on the charge is: • W=Vq =(1.00V)(1.60 x 10^-19J) • =1.60x10^-19J (this gain in potential energy is called the electronvolt, eV)

  19. Ex. • Moving a point charge of 3.2 x 10^-19 coulomb between points A and B in an electric field requires 4.8 x 10^-18 joules of energy. What is the potential difference between these points?

  20. Ex. • Moving a point charge of 3.2 x 10^-19 coulomb between points A and B in an electric field requires 4.8 x 10^-18 joules of energy. What is the potential difference between these points? • V=W/q 4.8x10^-18J / 3.2x10^-19C =

  21. Ex. • Moving a point charge of 3.2 x 10^-19 coulomb between points A and B in an electric field requires 4.8 x 10^-18 joules of energy. What is the potential difference between these points? • V=W/q 4.8x10^-18J / 3.2x10^-19C = 15V

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