Bound Current
Bound current refers to the flow of electric current within a material, such as a conductor or semiconductor, due to the movement of bound charges. These bound charges can be electrons in a conductor or electron-hole pairs in a semiconductor. Bound current is an important concept in understanding the behavior of materials in the presence of electric fields.
3 Key excerpts on "Bound Current"
eBook - ePub- Adrian Waygood(Author)
- 2018(Publication Date)
- Routledge(Publisher)
...In this case, the direction of conventional -current drift (i.e. positive to negative) is downward. When viewed from above, it will be seen the individual compass needles have now assumed a clockwise direction around the conductor. Finally, in Figure 17.1c, the battery connection is reversed, so that the conventional current drift through the conductor is now upwards. This time, it will be seen that the individual compass needles have reversed direction, and have now assumed a counterclockwise direction around the conductor. From this simple experiment, we can conclude that: An electric current is always surrounded by a magnetic field. The ‘direction’ of the magnetic field depends upon the direction of the current. When we describe a magnetic field as ‘surrounding a current’, it applies whether or not there is a conductor present. For example, a magnetic field will also surround an arc, which is a current passing through air or a vacuum. Remember, as we learned in the chapter on magnetism, a magnetic field consists of magnetic flux the direction of which, by common agreement, is determined by the direction in which a compass needle will point, when placed within that magnetic field – i.e from north to south. Electromagnetic fields Before proceeding further, we need to learn how the direction of an electric current is represented, graphically, in this and in all other texts. Imagine releasing an arrow in the same direction as the current (Figure 17.2). With the arrow moving away from you, you will see its flight feathers represented by a cross (×) but, if the arrow is coming towards you, then you will see its point, represented by a dot (•)...
eBook - ePub- Wen Geyi(Author)
- 2011(Publication Date)
- Wiley(Publisher)
...The final equation shows that there are no free magnetic monopoles and that the magnetic field also obeys the inverse square law. It should be understood that none of the experiments had anything to do with waves at the time when Maxwell derived his equations. Maxwell equations imply more than the experimental facts. The continuity equation can be derived from (1.21) as (1.22) Remark 1.1: The charge density ρ and the current density J in Maxwell equations are free charge density and currents and they exclude charges and currents forming part of the structure of atoms and molecules. The bound charges and currents are regarded as material, which are not included in ρ and J. The current density normally consists of two parts: J = J con + J imp. Here J imp is referred to as external or impressed current source, which is independent of the field and delivers energy to electric charges in a system. The impressed current source can be of electric and magnetic type as well as of non-electric or non-magnetic origin. J con = σ E, where σ is the conductivity of the medium in mhos per meter, denotes the conduction current induced by the impressed source J imp. Sometimes it is convenient to introduce an external or impressed electric field E imp defined by J imp = σ E imp. In a more general situation, one can write J = J ind (E, B) + J imp, where J ind (E, B) is the induced current by the impressed current J imp. Remark 1.2 (Duality): Sometimes it is convenient to introduce, magnetic current J m and magnetic charges ρ m, which are related by (1.23) and the Maxwell equations must be modified as (1.24) The inclusion of J m and ρ m makes Maxwell equations more symmetric. However, there has been no evidence that the magnetic current and charge are physically present. The validity of introducing such concepts in Maxwell equations is justified by the equivalence principle, that is, they are introduced as a mathematical equivalent to electromagnetic fields...
eBook - ePub- Gilbert M. Masters(Author)
- 2013(Publication Date)
- Wiley-IEEE Press(Publisher)
...The combinations of resistors, capacitors, inductors, voltage sources, current sources, and so forth, that you see in a circuit diagram are merely models of real components that comprise a real circuit, and a certain amount of judgment is required to decide how complicated the model must be before sufficiently accurate results can be obtained. For our purposes, we will be using very simple models in general, leaving many of the complications to more advanced textbooks. 2.2 DEFINITIONS OF KEY ELECTRICAL QUANTITIES We shall begin by introducing the fundamental electrical quantities that form the basis for the study of electric circuits. 2.2.1 Charge An atom consists of a positively charged nucleus surrounded by a swarm of negatively charged electrons. The charge associated with one electron has been found to be 1.602 × 10 −19 coulombs; or, stated the other way around, one coulomb can be defined as the charge on 6.242 × 10 18 electrons. While most of the electrons associated with an atom are tightly bound to the nucleus, good conductors, like copper, have free electrons that are sufficiently distant from their nuclei that their attraction to any particular nucleus is easily overcome. These conduction electrons are free to wander from atom to atom, and their movement constitutes an electric current. 2.2.2 Current In a wire, when one coulomb's worth of charge passes a given spot in one second, the current is defined to be one ampere (A), named after the nineteenth-century physicist André-Marie Ampère. That is, current i is the net rate of flow of charge q past a point, or through an area: (2.1) In general, charges can be negative or positive. For example, in a neon light, positive ions move in one direction and negative electrons move in the other. Each contributes to current, and the total current is their sum...
