(39) Current, Resistance, and Ohm's Law

(39) Current, Resistance, and Ohm's Law - Lecture 39...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon

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

View Full DocumentRight Arrow Icon

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

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Lecture 39 Current. Resistance. Ohm’s law. Electric current Electric current = charges in motion. Units: A (Ampere) 1 A = 1 C/ s dQ I dt = Current f or unif or m cur r ent A dI I J dA = = Current density (current per cross- sectional area) A = cross-sectional area (Example: cross-section of a wire of radius r is π r 2 ) I n terms of microscopic quantities… I n terms of microscopic quantities… dA current Current density = charge that goes though a cross-section of area dA in a time interval dt n = density of carriers (~ 10 29 m 3 − ) car r ier d J q nv = char ge J dA dt = (char ge densit y)(volume) dA dt = ( 29 ( 29 car r ier d q n v dt dA dA dt = v d dt v d = drift velocity (average velocity of carriers) = charge in the box Historical parenthesis Historical parenthesis For historical reasons, even though we now know that the carriers are usually negative (electrons), current I is usually defined as positive from higher to lower potential . This means, opposite to the actual motion of the electrons, or as if the positive charges were the ones...
View Full Document

This note was uploaded on 03/27/2008 for the course PHYS 221 taught by Professor Herrera-siklody during the Fall '08 term at Iowa State.

Page1 / 15

(39) Current, Resistance, and Ohm's Law - Lecture 39...

This preview shows document pages 1 - 5. Sign up to view the full document.

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