tailieunhanh - Crc Press Mechatronics Handbook 2002 By Laxxuss Episode 1 Part 7

Tham khảo tài liệu 'crc press mechatronics handbook 2002 by laxxuss episode 1 part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | since current consists of the flow of very large numbers of charge particles. The other charge-carrying particle in an atom the proton is assigned a positive sign and the same magnitude. The charge of a proton is qp X 10 19 coulomb Electrons and protons are often referred to as elementary charges. Electric current is defined as the time rate of change of charge passing through a predetermined area. If we consider the effect of the enormous number of elementary charges actually flowing we can write this relationship in differential form dq i dt C sec The units of current are called amperes A where 1 A 1 C sec. The electrical engineering convention states that the positive direction of current flow is that of positive charges. In metallic conductors however current is carried by negative charges these charges are the free electrons in the conduction band which are only weakly attracted to the atomic structure in metallic elements and are therefore easily displaced in the presence of electric fields. In order for current to flow there must exist a closed circuit. Figure depicts a simple circuit composed of a battery . a dry-cell or alkaline battery and a light bulb. Note that in the circuit of Fig. the current i flowing from the battery to the resistor is equal to the current flowing from the light bulb to the battery. In other words no current and therefore no charge is lost around the closed circuit. This principle was observed by the German scientist . Kirchhoff and is now known as Kirchhoff s current law KCL . KCL states that because charge cannot be created but must be conserved the sum of the currents at a node must equal zero in an electrical circuit a node is the junction of two or more conductors . Formally Lin 0 Kirchhoffs current law n 1 The significance of KCL is illustrated in Fig. where the simple circuit of Fig. has been augmented by the addition of two light bulbs note how the two nodes that exist in