ch26_lecture_notes

ch26_lecture_notes - Chapter 26 Currents in materials In...

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Chapter 26 Currents in materials In this chapter we will study the following topics : 1. The notion of electric current ( I ) 2. The motion of charges in current carrying conductors 3. The notion of resistance 4. The relation between the voltage V applied across a conductor and the resulting current I (Ohm’s law) 5. The power dissipated as heat on a current carrying conductor (26-1)
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conductor + - A Electric current (symbol: I) Electric current I is defined as the amount of charge Q that passes through a given area A of a conductor in time t Units of I: C/s known as the “Ampere” I is a scalar because it is defined as a ratio of two scalars. Nevertheless, we associate a direction to I according to the following recipe: (26-2) Q I t
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Convention on the direction of the electric current I I +q v conductor The current is due to the motion of positive charges . The direction of the current is defined to be parallel to the charge velocity v The current is due to the motion of negative charges . The direction of the current is defined to be antiparallel to the charge velocity v Note: Moving charges are known as “ carriers I -q v conductor (26-3)
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I +q v conductor J A -q v conductor A I J Current density vector J Magnitude: Units of J: A/m 2 Direction: J is parallel to the conventional direction of the current I (26- 4) I J A
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General case: J
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ch26_lecture_notes - Chapter 26 Currents in materials In...

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