PHY108 - Chapter 26

PHY108 Chapter 26 - Chapter 26 Currents in Materials Questions to Answer o What is electric current o What is electric current density o What is an

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Unformatted text preview: Chapter 26: Currents in Materials Questions to Answer o What is electric current? o What is electric current density? o What is an ohmic conductor? o What is resistivity? What is resistance? What is a resistor? o What is the equivalent resistance of two resistors connected in parallel? o What is the equivalent resistance of two resistors connected in series? o What is power dissipated in a resistor and where does the energy go? Ch. 26 Current and Resistance C Current C Ohm’s Law C Conductivity, Resistivity and Resistance C Microscopic model for movement of charges in conductors: Drude model C Temperature dependence of resisitivity C Electrical Energy and Power Previous Chapters covered electro statics , meaning charges were not moving. E.G. when discussing conductors we determined the electric field and voltages when the charges were no longer moving. We will now discuss charges in motion . Current Current x x v t ∆ ∆ ∆ = How do get this? 1. With a bucket and a watch 2. measure the velocity of the water and at same point the cross sectional area = A Total volume passing through area A Vol=A x= Vol v v t A t A ∆ ∆ ∆ ∆ ∆ = How much water flows over the falls per second? • Flow rate = 1400 - 2800 m 3 /s Volume passing point P per unit time Water Current = Vol/ t? ∆ ∆ Electrical Current How much charge passes through a section of wire per unit time? x x v t ∆ ∆ ∆ = d Q Electric Current = I = nqAv t ∆ ∆ = q q q q n = # carrier/Vol. In conductor moving charges called charge carriers with charge q. passing point P per unit time = Electrical Current =I= Ch rge t a Q/ ? ∆ ∆ d Charge passing through area A in time t Q nq V=nqA x=nqAv t ∆ ∆ ∆ ∆ ∆ = d Q Electric Current = I = nqAv t ∆ ∆ = Electric current proportional to the density of carriers, the drift speed and the charge, q. NOTE: the current direction is the same direction as the flow of POSITIVE CHARGE....
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This note was uploaded on 10/10/2010 for the course PHY 108 taught by Professor Iashvili during the Spring '08 term at SUNY Buffalo.

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PHY108 Chapter 26 - Chapter 26 Currents in Materials Questions to Answer o What is electric current o What is electric current density o What is an

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