chapter17_PC - Chapter17 CurrentandResistance...

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
    Chapter 17 Current and Resistance
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
    Electric Current Whenever electric charges of like signs move,  an  electric current  is said to exist The current is the  rate at which the charge  flows through this surface Look at the charges flowing perpendicularly to a  surface of area A The SI unit of current is Ampere (A) 1 A = 1 C/s Q I t
Background image of page 2
    Electric Current, cont The direction of the current is the direction  positive charge would flow This is known as  conventional current direction In a common conductor, such as copper, the current is  due to the motion of the negatively charged electrons It is common to refer to a moving charge as a  mobile  charge carrier A charge carrier can be positive or negative
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
    Current and Drift Speed Charged particles move  through a conductor of  cross-sectional area A n is the number of  charge carriers per unit  volume n A Δx is the total  number of charge  carriers
Background image of page 4
    Current and Drift Speed, cont The total charge is the number of carriers  times the charge per carrier, q ΔQ = (n A Δx) q The drift speed, v d , is the speed at which the  carriers move v d  = Δx/ Δt Rewritten: ΔQ = (n A v d  Δt) q Finally, current, I = ΔQ/Δt = nqv d A
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
    Current and Drift Speed, final If the conductor is isolated, the  electrons undergo random motion When an electric field is set up in the  conductor, it creates an electric force on  the electrons and hence a current
Background image of page 6
    Charge Carrier Motion in a  Conductor The zig-zag black line  represents the motion  of charge carrier in a  conductor The net drift speed is  small The sharp changes in  direction are due to  collisions The net motion of  electrons is opposite the  direction of the electric  field
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
    Electrons in a Circuit The drift speed is much smaller than the  average speed between collisions When a circuit is completed, the electric field  travels with a speed close to the speed of  light Although the drift speed is on the order of 10 -4   m/s the effect of the electric field is felt on the  order of 10 8  m/s
Background image of page 8
    Meters in a Circuit – Ammeter  An ammeter is used to measure current In line with the bulb, all the charge passing  through the bulb also must pass through the meter
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
    Meters in a Circuit – Voltmeter  A voltmeter is used to measure voltage  (potential difference) Connects to the two ends of the bulb
Background image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 05/17/2011 for the course PHY 2054 taught by Professor Avery during the Spring '08 term at University of Florida.

Page1 / 39

chapter17_PC - Chapter17 CurrentandResistance...

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online