This preview shows pages 1–6. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: Current & Resistance Current & Resistance  Current and current density Ohms Law Resistivity Resistance Electrical Current Electrical Current CURRENT I is the amount of positive charge flowing past a fixed point in the wire per unit time : if charge dQ flows in time dt Units : 1 ampere (A) = 1 C/s Direction : by convention, current is the direction of movement of positive charge + + + + + + I I dQ I dt = Electron Velocities Electron Velocities Random velocities of electrons are large (several km/s) Drift velocity is a slow, average motion parallel to E start end start end net displacement + ( ) F e E = + r E no field Charge Q in length L of wire passes through the shaded disk of area A in time t : Q = (number of charge carriers/volume) x (charge on each one) x volume + + + + + + + + + + + + L = v d t E Determining the current Current: I = Q/ t = nqAv d t / t So, Charge: Q = n q V = n q (AL) = n q A v d t (since L=vt) I = nqAv d v d = average (drift) velocity of each charge q = charge on each particle n = number of charge carriers per unit volume A = cross section area L = length AL = volume Example...
View Full
Document
 Spring '08
 jopko
 Physics, Charge, Current, Resistance

Click to edit the document details