# PHYS 1B Lecture Notes - Lecture 12: Printed Circuit Board, Electrical Network, R V R

## Document Summary

Resistivity and conductivity: experiments show that resistance of an ohmic conducting wire (most metals, Increase with increasing length l of the wire assumed to be circular in cross section) is given by: r = pl/a. P = resistivity of material; depends on atoms and their arrangements. Conductivity defined as sigma = 1/p: higher resistance = lower conductivity. Ex: copper wires often used in home electrical wiring resistivity of copper is 1. 7e-8 ohm*meter. Resistors: resistor is a simple circuit element that provides a resistance in a circuit that obeys. Oh(cid:373)"s la(cid:449: resistors on a circuit board. If you open a computer, tv, microwave, etc. you see many resistors on the circuit boards. Ex: resistor and voltmeter used to determine current flowing through one path (wire) of an electric circuit. Suppose 200 ohm resistor is inserted in the path of a wire and a voltmeter reads that there is a potential difference of 1. 5 v across the resistor.