PHY132_L10 - Classical Physics II PHY132 Lecture 10...

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

View Full Document Right Arrow Icon
Lecture 10 1 Classical Physics II PHY132 Lecture 10 Circuits 02/17/2010
Background image of page 1

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

View Full DocumentRight Arrow Icon
02/17/2010 Lecture 10 2 Resistance The resulting current through the conducting wire of Ø A is I = dQ/dt = q n q ( Adx ) /dt = qn q Av d , – where n q is the density of charge carriers in the conductor (#/m 3 ), – and q the charge of a single carrier; we assume that all carriers are of the same type (e.g. electrons). Because v d is proportional to E : I = qn q Av d ( qn q ) AE E ( =V/L ) = I/A j where j is the “current density” in the wire. – The proportionality constant is dependent on material, temperature, and typically not even constant with voltage… – the material “constant” is called “ resistivity – the total resistance R of the wire is defined as: R = V/I = ( V/L )/( I/A ) L/A = L/A Units: [ j ] = A/m 2 = C/m 2 /s , Resistance: [ R ] = V/A• Ohm = • Resistivity: [ ] = (V/m)/(A/m 2 ) = Vm/A • Ohm ·m = • m Ohm’s “Law” : V = I R , or: V/L = I/A
Background image of page 2
3 Resistors Typical metals have low resistivity (high conductivity ): • 1–100 10 –8 • m = 0.01–1 10 –2 • mm 2 /m Typical insulators have high resitivity : • 10 8 • m In electronics, resistors are either metal - wire/film or carbon resistors, with color coded values… Common resistor values : R = 0.1 • – 100 M• ( 1%, 5%, 10%) Symbols: Systems of resistors: Series: R tot = R 1 + R 2 Parallel: I tot = I 1 + I 2 V ab / R tot = V ab / R 1 + V ab / R 2 1/ R tot = 1/ R 1 + 1/ R 2 (as for Caps in SERIES !) R R 1 R 2 a b c R 1 R 2 a b R 02/17/2010 Lecture 10 (a thin wire wrapped on an insulating rod)
Background image of page 3

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

View Full DocumentRight Arrow Icon
02/17/2010 Lecture 10 5 RC Circuit Connecting a charged capacitor to a resistor gets current to flow, which slowly decreases until the capacitor is fully drained: After switch S is closed ( t =0 ): And equivalently: Note the CHARACTERISTIC TIME RC ; – after t=RC charge, current, and voltage are down to 1/e , after t= 2 RC , they are down to 1/e 2 , etc.
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/14/2010 for the course PHY 132 taught by Professor Rijssenbeek during the Spring '04 term at SUNY Stony Brook.

Page1 / 12

PHY132_L10 - Classical Physics II PHY132 Lecture 10...

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