Lecture%2012%202220%20Spring%202009

# Lecture%2012%202220%20Spring%202009 - Announcements and...

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1 Announcements and Reminders HW 8 is due Friday Exam 1 is next Monday starting at 4:15 p.m. Help room (Physics 117) hours: Monday 4-8 pm Tuesday and Wednesday 3 6:30 pm Tuesday and Wednesday 3-6:30 pm Thursday 4:30-8 pm Friday 2-6 pm I have the signup sheet for the nuclear power plant trip if you are interested. Turn in a piece of paper with name and responses if you don’t have your clicker with you today, or if you haven’t given me your clicker ID yet Chapter 27 Current and Resistance Electric Current Electric current is the rate of flow of charge through some region of space • The SI unit of current is the amper (A The SI unit of current is the ampere (A) 1 A = 1 C / s • The symbol for electric current is I Average Electric Current • Assume charges are moving perpendicular to a surface of area A a surface of area • If Δ Q is the amount of charge that passes through A in time Δ t , then the average current is av Q t Δ = Δ I Instantaneous Electric Current If the rate at which the charge flows varies with time, the instantaneous current, I , can be found I dQ dt = Direction of Current • The charges passing through the area could be positive or negative or both • It is conventional to assign to the current the same direction as the flow of positive charges • The direction of current flow is opposite the direction of the flow of electrons • It is common to refer to any moving charge as a charge carrier

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2 Rank the currents from most positive to most negative (positive being to the right).
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## This document was uploaded on 09/30/2009.

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Lecture%2012%202220%20Spring%202009 - Announcements and...

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