Electric Current
Electric current is the flow of electric charge through a conductor. It is measured in amperes (A) and is the rate of flow of electric charge past a point in a circuit. The flow of current is driven by a potential difference, or voltage, and is fundamental to the operation of electrical devices and systems.
8 Key excerpts on "Electric Current"
eBook - ePub- Howard W. Penrose(Author)
- 2014(Publication Date)
- Success By Design(Publisher)
...Insulators include ceramics, glass and mica. Current, Voltage and Resistance Whether discussing the topic in terms of direct or alternating current, the basic elements of electricity include current, voltage and resistance. Current (I) is the flow of electricity much like the flow of water in a pipe. It is measured in Amperage as opposed to gallons per minute of water. The measurement of current is standardized as 1 Amp being equal to 6.28 × 10 18 electrons passing one point in one second. This value is also termed as 1 Coulomb of electrons being equal to one Amp. The electron charge is therefore equal to 1.60219 × 10 –19 Coulombs. For the purpose of this book, we will determine that amperage flows from the negative (excess electrons) charge to positive charge. Voltage (V or E) is the electrical pressure in the system much like water pressure in a pipe. Electrical pressure is measured in Volts as opposed to pounds per square inch and the greater the value of Voltage, the greater the electrical pressure. This can also be considered ‘electrical potential,’ with 1 Volt equaling 1 Joule/Coulomb (Q) representing the work to move the electrical charge against a field. If we now consider this as being similar to air pressure in a compressed air system, if both the inside of the compressed air system is equal to the outside, then no current will flow. If the pressure inside the system increases, the potential energy to move current increases. This is an important concept that we will explore later as, in order to determine Voltage, we must have a reference. For example, if you were standing in a room and the floor had a potential equal to 4,160 Volts to the hallway outside and a table in the room had a potential equal to 4,160 Volts, you would be able to touch the table and walk around in the room safely...
eBook - ePubInstrumentation
An Introduction for Students in the Speech and Hearing Sciences
- T. Newell Decker, Thomas D. Carrell(Authors)
- 2004(Publication Date)
- Psychology Press(Publisher)
...This energy then flows through wires to outlets such as those in your home or apartment. FIG. 1.5. A schematic representation of (a) alternating current and (b) direct current. In addition to providing power to equipment, AC energy is also present in other forms. For example, a pure tone signal delivered by an audiometer to an earphone is alternating current. So also is the speech signal produced by your vocal apparatus. Whereas the former consists of a single alternating voltage, the latter will have a complex of alternating voltages. In DC circuits the amount and direction of the voltage are always constant, with either a positive or negative value. Direct current is most often produced by batteries. Because batteries are a convenient and portable method of storing electricity, direct current is usually the power on which portable equipment runs. Figure 1.5 b shows DC current coming on with a positive polarity, staying constant, and then being turned off and returning to zero volts. CURRENT, VOLTAGE, RESISTANCE Current, voltage, and resistance are three fundamental factors present in every electrical circuit. Therefore, it is important that you have a basic understanding of each. Current The word current, refers to running or flowing, and in electrical terms it means a flowing of free electrons. Current (I) is defined as the number of free electrons that pass through a given point divided by the time that it takes them to pass. Measuring the passage of a single electron would be a formidable task, so a much larger quantity is needed. This standard quantity is the coulomb (C), which is the metric measure for electric charge (Q). One coulomb equals the electric charge that exists or the amount of electricity present on 6.24 × 10 18 protons or electrons...
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...
eBook - ePub- Julian Nathan(Author)
- 1998(Publication Date)
- Newnes(Publisher)
...1.1 is open, voltage is present across the battery and therefore across the switch. But no current flows. Fig. 1.1 An electric circuit. 2. When the switch is closed, current flows through the (lamp) load, limited by the combined resistance of the load, the source, the conductors, and the switch. 3. Work (Watts) done in the load equals electrical pressure (Volts) times current (Amps). A small proportion is wasted in heating the other resistive components, including the battery. 4. The current (flow) at any point in the circuit is the same at any other point (in a simple circuit that does not branch). 5. Electricity requires a complete circuit for current to flow. ELECTRICAL PRINCIPLES Volts, Amps (amperes) and Ohms are inter-related quantities, and refer to the physical properties of Electricity. Without an easily acquired understanding of these three basics, very little progress can be made in any application. A working knowledge is given in the following few pages, containing nothing more complex than simple equations. Voltage is Electrical Pressure. Just as water in a tank exerts physical pressure on the pipe it supplies, so a voltage source exerts electrical pressure, or a potential difference, at the parts of a circuit to which it is connected. Voltage is also referred to as Electromotive Force, or EMF. VOLT : The unit of ELECTRICAL PRESSURE Symbol : V Amperes denote Electric Current Flow. When pressure is released, water in a pipe flows. The flow rate could be expressed in liters per minute. A fundamental observation is that the flow rate is the same at any point in the pipe, assuming it does not branch. Three liters per minute at one end guarantees three liters per minute at the other. Electric Current flow is the same. AMP : The unit of Electric Current FLOW Symbol : I Ohms are units of Electrical Resistance (to current flow). Again consider the water pipe. If it is rough inside, or narrow, it could be said to have high resistance...
eBook - ePubElectrical Engineering
Fundamentals
- Viktor Hacker, Christof Sumereder(Authors)
- 2020(Publication Date)
- De Gruyter Oldenbourg(Publisher)
...1 The basic physic principles and definitions 1.1 The simple circuit In everyday life, people do not distinguish between technically correct designations for electric quantities but abbreviate and incorrectly name it “electricity”. Colloquially, the expression “electricity bill” is used, when in reality the electrical energy consumption is meant; when an electrical accident happens, it is referred to as “electric shock”. A person with technical knowledge is aware that a flow of an electric charge is designated “Electric Current” and that the physical quantity of current (intensity) uses the unit ampere. Furthermore, an expert knows that it is the voltage (measured in volts) that drives the current and that resistance (measured in ohm) at constant voltage determines the current (Figure 1.1). To better understand the correlation between Electric Current, voltage and resistance, we look at the water cycle as analogue to the electric circuit. Figure 1.1: Correlation between current, voltage and resistance. Table 1.1: Water cycle as analogue to electric circuit. Water cycle (analogue) Electric circuit Figure 1.2: Closed water cycle. Figure 1.3: Closed circuit. The flow of water Q t is caused by the pressure difference Δ P generated by pump P. The current flow is caused by the potential difference (= voltage V) generated by the voltage source. The pressure difference Δ P determines the amount of water pumped via the load per time. The potential difference (voltage V) determines the electric charge per time (current I) flowing through the load. The pressure loss due to the resistance in the container C is as high as the pressure...
eBook - ePub- Adrian Waygood(Author)
- 2018(Publication Date)
- Routledge(Publisher)
...The new definition will likely describe the ampere in terms of the movement of a specific number of individual electrons per unit time past a given point in a conductor. The amount of charge transported, per second, by a current of one ampere is one coulomb (symbol: C). The coulomb is equivalent to the amount of charge generally rounded off to 6.24×1018 electrons. This figure will be defined to a greater level of accuracy once the ampere is redefined in 2019. Misconceptions The ampere is defined in terms of the rate of drift of electric charge Current is defined as the quantity of charge transported per unit time. But, at present, its unit, the ampere is defined in terms of the force between current-carrying conductors. Proposed changes will likely mean that, from May 2019, the ampere will be redefined in terms of the rate of flow of elementary charges (individual electrons), not coulombs. The ampere describes the speed of an Electric Current The ‘speed’ of an Electric Current has nothing to do with its unit of measurement. Electric charge drifts v-e-r-y slowly, regardless of the value of current. Review your learning Now that we’ve completed this chapter, we need to examine the objectives listed at its start. Placing ‘ Can I… ’ at the beginning, and a question mark at the end, of each objective turns that objective into a test item. If we can answer each of those test items, then we’ve met the objectives of this chapter. Online resources The companion website to this book contains further resources relating to this chapter. The website can be accessed via the following link: www.routledge.com/cw/waygood An Introduction to Electrical Science, Waygood, ISBN 9780815391821, 2019. © Taylor & Francis...
- S. Bobby Rauf(Author)
- 2021(Publication Date)
- River Publishers(Publisher)
...This circuit consists of a DC voltage source labeled “V.” As explained earlier, voltage is synonymous to the term electromotive force. So, we can explain the phenomenon in the electrical circuit as the electromotive force “V” driving DC current “I” through the load or resistor “R.” Note that the direction of the current is from the left to right, in a clockwise loop, emerging from the positive electrode of the DC voltage source and terminating into the negative electrode of the voltage source. This clockwise current flow is assigned on the basis of an electrical convention that stipulates that the current flow consists of “holes,,” or positively charged particles, being repelled or driven out of the positive terminal. This convention also affirms the fact that electrical current is not necessarily, always, due to the flow or movement of electrons. Electrical current, as explained in the section on the topic of current, can be due the flow or movement of negatively or positively charged particles. The positively or negatively charged particles, at the atomic or molecular level, are referred to as ions. The relationship between V, I, and R in the electrical circuit is governed by the Ohm’s law. The Ohm’s law, in conjunction with other basic electrical laws — used to analyze electrical circuits — will be explained in more detail in Chapter 2. For now, note that the Ohm’s law is stated, mathematically, in the form of Eq. 1.41. In other words, according to Ohm’s law, electromotive force is equal to the product of current and resistance. E l e c t r o m o t i v e F o r c e, V = I. R = (C u r r e n t) × (Re s i s tan c e) Eq. 1.41 The circuit shown in Figure 1.25 (b) represents a basic electromagnetic circuit. This circuit consists of a toroid- or donut-shaped core, typically constructed out of iron. In this magnetic circuit, a conductor, or wire, is wrapped in four turns around the left side of the toroid core...
eBook - ePub- S. Bobby Rauf(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...The positively or negatively charged particles at the atomic or molecular level are referred to as ions. The relationship between V, I, and R in the electrical circuit is governed by Ohm’s law. Ohm’s law, in conjunction with other basic electrical laws – used to analyze electrical circuits – will be explained in more detail in Chapter 2. For now, note that Ohm’s law is stated, mathematically, in the form of Eq. 1.41. In other words, according to Ohm’s law, electromotive force is equal to the product of current and resistance. E l e c t r o m o t i v e F o r c e, V = I ⋅ R = (C u r r e n t) × (R e s i s t a n c e) (1.41) The circuit shown in Figure 1.26b represents a basic electromagnetic circuit. This circuit consists of a toroid or donut-shaped core – typically constructed out of iron. In this magnetic circuit, a conductor, or wire, is wrapped in four turns around the left side of the toroid core. When current is passed through wound conductor, magnetic field is established in the core as represented by the dashed circular line, with an arrow pointing in clockwise direction. This magnetic field is referred to as magnetic flux, ф. Magnetic flux is measured in weber. The unit weber is named for the German physicist Wilhelm Eduard Weber (1804–1891). In the magnetic realm, the flux serves as a counterpart to the current, I, from the electrical realm. Just like the electromotive force, EMF, or voltage, drives the current through the resistor, R, the magnetomotive force (MMF), F, drives the magnetic flux, ф, through the toroid magnetic core. Magnetomotive force is measured in ampere-turns. In electrical systems, load is represented by the resistor R. In the magnetic circuit, the flow of magnetic flux is opposed by reluctance R. Just as Ohm’s law, represented by Eq. 1.41, governs the relationship between electromotive force (voltage), current, and resistance in the electrical realm, Eq...
