lecture 10 - Chapter 31 Fundamentals of Circuits 1...

Info iconThis preview shows pages 1–14. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Fundamentals of Circuits Chapter 31
Background image of page 1

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

View Full DocumentRight Arrow Icon
2 Capacitors in Series + - + - V 1 V + - 2 V 1 C 2 C 1 2 V V V = ∆ + ∆
Background image of page 2
3 Conductor in Electric Field no electric field E r E r E r equilibrium 0 E = r
Background image of page 3

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

View Full DocumentRight Arrow Icon
4 Conductor in Electric Field no electric field E r E r conducting wire conducting wire E r ELECTRIC CURRENT
Background image of page 4
5 Electric Current Electric current is the rate of flow of charge through some region of space The SI unit of current is the ampere (A), 1 A = 1 C / s Assume charges are moving perpendicular to a surface of area A If Q is the amount of charge that passes through A in time t , then the average current is av Q t = I
Background image of page 5

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

View Full DocumentRight Arrow Icon
6 Ohm’s Law Chapter 28 Chapter 31
Background image of page 6
7 Current Density I j A = Current density is defined as the current per unit area This expression is valid only if the current density is uniform and A is perpendicular to the direction of the current j has SI units of A/m 2
Background image of page 7

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

View Full DocumentRight Arrow Icon
8 Ohm’s Law j E σ = Ohm’s Law: Current density is proportional to electric field E r The constant of proportionality, σ , is called the conductivity of the conductor. The conductivity depends only on the material of conductor. 2 n q m τ σ= Simplified model of electron motion in conductor gives - is the material dependent characteristic of conductor.
Background image of page 8
9 Ohm’s Law Ohm’s law states that for many materials, the ratio of the current density to the electric field is a constant σ that is independent of the electric field producing the current Most metals, but not all, obey Ohm’s law Materials that obey Ohm’s law are said to be ohmic Materials that do not obey Ohm’s law are said to be nonohmic Ohm’s law is not a fundamental law of nature Ohm’s law is an empirical relationship valid only for certain materials j E σ =
Background image of page 9

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

View Full DocumentRight Arrow Icon
10 Ohm’s Law Conductor E r A B Voltage across the conductor (potential difference between points A and B ) B A V V V El = - = l where electric field is the same along the conductor. Then V E l = I j A = 1 V I E j l A σ = = = j E = l V I RI A = = Another form of the Ohm’s Law
Background image of page 10
11 Ohm’s Law: Resistance Conductor E r A B l V RI = The voltage applied across the ends of the conductor is proportional to the current through the conductor The constant of proportionality is called the resistance of the conductor resistance SI units of resistance are ohms (Ω) 1 Ω = 1 V / A
Background image of page 11

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

View Full DocumentRight Arrow Icon
12 Ohm’s Law: Resistance Conductor E r A B l V RI = l R A σ = resistance l R A ρ = Or where is the resistivity – the inverse of the conductivity 1/ = Resistivity has SI units of ohm-meters (Ω m)
Background image of page 12
13 Resistance: Example Conductor l l
Background image of page 13

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

View Full DocumentRight Arrow Icon
Image of page 14
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/15/2012 for the course PHYS 2212 taught by Professor Staff during the Spring '08 term at Georgia State University, Atlanta.

Page1 / 47

lecture 10 - Chapter 31 Fundamentals of Circuits 1...

This preview shows document pages 1 - 14. Sign up to view the full document.

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