电工学武汉理工大学演示课件chapter1.pptVIP

Chapter1 Circuit Elements and Circuit Laws;1.1 Constitute of Circuit;2. Circuit and Circuit Model; ;1.2 Reference direction of voltage and current;Reference directions;Reference direction: often define direction of positive electric charge (or opposite direction of negative charge).;Direction： Action in electric field, positive electric charges move from higher potential to lower potential. Reference direction: define move direction of positive electric charge. Before analysis in electric circuit, choose any direction as reference direction of voltage. If direction between reference direction and factual direction is same, value of voltage is positive; or not, its value is negative. Unit： V, kV, mV;In figure relative direction voltage and current; Ohms law states that voltage across many types of conducting materials is directly proportional to the current flowing through the material. Expression:;Define symbol in Ohm’s law:;List expression in figure (a), (b), (c), (d )by Ohm’s law. R=?;Figure a;U;R0;U;If R0?R, then U? E ;If U=E-IR0 then UI= EI-I2R0 or P = PE - ? P;Source: factual direction of U and I is opposite, I sends out from “+” term, generate power. Load: factual direction of U and I is same, I flows in from “+” term, absorb power.;2. Open Circuit;3. Short circuit;1.4 Kirchhoff’s Laws;Kirchhoff’s laws: 1. Kirchhoff’s current law(KCL) ——apply in node 2. Kirchhoff’s voltage law(KVL) ——apply in loop;Nouns and Concepts;Nouns and Concepts;Kirchhoff’s current law—KCL;KCL states：the sum of the currents at a node must equal zero.;The KCL may be extended to the supernode:;Kirchhoff’s voltage law—KVL;;KVL another state : in circuit terms, the sum of all voltages associated with sources must equal the sum of the load voltages, so that the net voltage around a closed circuit is zero.;Application of KVL;Notice:;Notice:;;