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For more information, please see full course syllabus of AP Physics B
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Lecture Comments (1)

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Post by Rajah Cook on September 18, 2013

"Extra Example 1" tablet video is broken.

Electric Current

  • The current is the rate of flow of charge. If you take a cross-section of a wire and count how many Coulombs flow the cross-section in one second, the will be the current, expressed in C/s, or A (Ampere).
  • In a wire with uniform cross-sectional area A, the current can be shown to be equal to Anqv where n is the number of charge carriers (in conductors, these are electrons), q is the charge carried by a charge carrier, and v is the drift velocity of the charge carriers.
  • Ohm’s law: V = I R. The potential difference across a wire is equal to the resistance R of the wire, times the current in the wire.
  • For a wire of uniform cross-sectional area A and length L, the resistance is given by R = (rho) L / A, where rho is the resistivity of the material from which the wire is made.

Electric Current

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Definition 0:20
    • Consider a Wire ,Cylindrical
    • Cross Sectional Area
    • Crossing Charges Will be Counted
    • Amount of Charge Crosses Cross Sectional Area
    • Current I=q/t
    • Charges Flowing in Opposite Direction
    • Current Density
    • Applying Electric Field
  • Current in a Wire 15:24
    • Wire With a Cross Section Area A
    • Current Flowing to Right
    • How Much Charge Crosses Area A
    • Drift Velocity
    • Carriers in Cylinder
  • Ohm's Law 24:58
    • Va-Vb = Electric Field times Length of Wire
    • Ohm's Law
    • Consider a Copper Wire of 1m , Cross Sectional Area 1cm/sq
  • Temperature Effect 37:07
    • Heating a Wire
    • Temperature Co-Efficient of Resistivity
  • Battery EMF 43:00
    • Connecting a Resistance to Battery
    • Potential Difference at Terminal of Battery
  • Power 53:30
    • Battery Connected with a Resistance
    • Work Done on Charge
    • Energy Lost Per Second
  • Extra Example 1: Current
  • Extra Example 2: Water Heater