电路理论第一章要点分析.pptVIP

* * Answer:I1 =1A ;I2 =1.5A ; I =－0.5A T=0.6s, u same to ref.; I opposite to ref. T=1.8s, u opposite to ref.; I same to ref. * 此处加例子。 * then the u and i are said to be labeled with the passive sign convention. * * A loop is a closed path formed starting at a node, passing through a set of nodes, and returning to the starting node without passing through any nodes more than once. Since the node is composed of perfect conductors, the voltage (with respect to an appropriate reference) anywhere in a node is the same. 6 branches, 4 nodes, 7 loops * At any time, to any type of circuit. Node a：I1-I6-I3=0, or I1=I3 +I6 Node b：-I1-I2-I5=0, or I1+I2+I5=0 Node c：I2-I4+I6=0, or I2+I6=I4 * A voltage encountered + to - is positive. A voltage encountered - to + is negative. * A POSITIVE CHARGE GAINS Electrical ENERGY AS IT MOVES TO A POINT WITH HIGHER VOLTAGE AND RELEASES Electrical ENERGY IF IT MOVES TO A POINT WITH LOWER VOLTAGE. * The relation between the resistor voltage and its current is a straight line. * Is it always true that v = iR? ?only with the passive sign convention, Otherwise v = -iR. A true negative resistor delivers power. It is possible to construct negative resistors by using elements such as tunnel diodes. But these require additional sources of energy such as batteries for operation, and the delivered power come from those sources. * 欧姆开始使用的电源是伏达电堆，这种电堆的电动势不稳定，后来经人建议改用铋铜温差电池，一端放在沸水里，一端放在碎冰雪里，从而保证了电源电动势的稳定。电阻用粗细相同、长度不同的铜丝，两个盛水银的杯子作为电池与电阻连接的电极。欧姆独立地用库仑的方法制造了电流扭力秤，利用悬挂磁针的偏转角与电流强度成正比来测量电流强度。 * 短路前，I1＝0.03A, 短路后＝6A * Uab=-4V，12/7A。（电池流出电流15/7A，向左分给R4电流3/7A） * 2. Voltage and Reference Direction 电压及其参考方向 Voltage ,( u) is the work required to move a unit positive charge through an element. Unit: volt, V (1 V = 1 J/C) Voltage is conventionally taken as the potential drop. 电压的实际方向是电位降低。 + uab － a b U1 = 1V 1V 5? ＋ U1 － U2 = －1V － U2 ＋ The direction is indicated by polarity (+,－) or an arrow going from a to b. Vol