Chapter 26 - Chapter 26 Current and Resistance In this...

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Chapter 26 Current and Resistance In this chapter we will introduce the following new concepts: -Electric current ( symbol i ) -Electric current density vector (symbol ) J r
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Consider the conductor shown in fig. . All the points inside the conductor and on its surface are at the same potential. The free electrons inside the conductor move in random direct a Electric Current ions and thus there is no net charge transport. We now make a break in the conductor and insert a battery as shown in fig. . Points and are now at potentials and , respectively ( , the A B A B b A B V V V V V - = voltage of the battery). The situation is not static any more, but charges move inside the conductor so that there is a net charge flow in a particular direction. We define this net flow of electric charge as "electric current." A B
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i + q conductor v r i - q conductor v r Consider the conductor shown in the figure. It is connected to a battery (not shown) and thus charges move through the conductor. Consider one of the cross sections through the conductor ( or or aa bb v Current = rate at which charge flow C ). The electric current is defin urrent SI Unit: C/s, known as th ed e "ampere" s as cc i v An electric current is represented by an arrow, which has the same direction as the charge velocity. The sense of the current arrow is defined as follows: If the current is due to t Current Direction 1. he motion of charges, the current arrow is to the charge velocity . If the current is due to the motion of charges, the current arrow is to the charg e velo v parallel 2. an negative tipar po alle si e l tiv r city . v r dq i dt =
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i - q conductor v r A J r Current density is a vector that is defined as follows: Its magnitude is The direction of is the same as that of the current. The current throu gh J Current Density r 2 SI unit for : A / m J a conductor of cross-sectional area is given by the equation if the current density is constant. If
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This note was uploaded on 06/01/2008 for the course PHYS 232 taught by Professor Goksu during the Spring '08 term at Millersville.

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Chapter 26 - Chapter 26 Current and Resistance In this...

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