Physics
Resistors
Resistors are electrical components that impede the flow of current in a circuit. They are designed to have a specific resistance value, measured in ohms, which determines the amount of current that can pass through them. Resistors are commonly used to control the flow of electricity, limit current, and divide voltage in electronic circuits.
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eBook - PDFFundamentals of Electromagnetics
1Internal Behavior of Lumped Elements
- David Voltmer(Author)
- 2022(Publication Date)
- Springer(Publisher)
1 C H A P T E R 1 Resistors 1.1 Resistors: A FIRST GLANCE Resistors are the simplest of lumped elements that you already know from your circuits courses. They enable us to control voltage drops and current flow throughout lumped element circuits. The application of a voltage drop across a resistor causes a current to flow into the more positive terminal, through the resistor, and out of the negative terminal. The relationship of the voltage drop across a resistor, V R , to the current through it, I R , is known as Ohm’s law and is expressed as R = V R I R [Omega1] (1.1) where R is the value of the resistance expressed in ohms and denoted by the symbol Omega1. The resistance value is a function of the geometry and material composition of the resistor. R WIRE R RESISTOR R ELECTROD R WIRE R ELECTROD (a) (b) FIGURE 1.1: Structure of a resistor: (a) phys- ical view and (b) electrical model. This chapter focuses upon the internal workings of the resistor and how to calculate its resistance. The structure of a typical resistor is of the form sketched in Fig. 1.1. The wire leads and the electrodes of a resistor are made of a good conduc- tor, usually copper, which has a very small resis- tance. That means that there is a very little voltage drop across the electrodes regardless of the mag- nitude of the current. Current flow between the two electrodes is through the conductive material between them. The conductive material greatly impedes the current and governs the resistor’s value. The con- ductive material of Resistors can take on a wide variety of composition and shape depending upon the application for which the resistor is intended. This structure is usually hermetically encap- sulated to protect it against external substances that could alter its value. 2 FUNDAMENTALS OF ELECTROMAGNETICS 1 1.2 MODELING AND APPROXIMATIONS Before proceeding further in the analysis of Resistors, let’s be clear about our strategy in solving electromagnetic problems.
eBook - PDF- Stephen Herman(Author)
- 2019(Publication Date)
- Cengage Learning EMEA(Publisher)
Preview R esistors are one of the most common components found in electric circuits. The unit of measure for resistance (R) is the ohm, which was named for a German scientist named Georg S. Ohm. The symbol used to represent resistance is the Greek letter omega ( V ). Resistors come in various sizes, types, and ratings to accommodate the needs of almost any circuit applications. 5–1 Uses of Resistors Resistors are commonly used to perform two functions in a circuit. One is to limit the flow of current through the circuit. In Figure 5–1, a 30-ohm resistor is connected to a 15-volt battery. The current in this circuit is limited to a value of 0.5 ampere. I 5 E R I 5 15 V 30 V I 5 0.5 A If this resistor were not present, the circuit current would be limited only by the resistance of the con-ductor, which would be very low, and a large amount of current would flow. Assume, for example, that the wire has a resistance of 0.0001 ohm. When the wire is connected across the 15-volt power source, a current of 150,000 amperes would try to flow through the circuit (15 V/0.0001 V 5 150,000 A). This is commonly known as a short circuit. FIGURE 5–1 Resistor used to limit the flow of current. + 15 V 3O 0.5 A Copyright 2020 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. UNIT 5 Resistors 105 The second principal function of Resistors is to produce a voltage divider. The three Resistors shown in Figure 5–2 are connected in series with a 17.5-volt battery.
eBook - PDF- Ian R. Sinclair(Author)
- 2013(Publication Date)
- Newnes(Publisher)
Chapter 1 Passive Components Resistors Resistance, measured in ohms (Ω), is defined as the ratio of voltage (in volts) across a length of material to current (in amperes) through the material. When a graph is drawn of voltage across the material plotted Ammeter Voltage readings o I Current readings (b) Figure 1.1. (a) A circuit for checking the behaviour of a resistor, (b) The shape of the graph of voltage plotted against current for an oh mie resistor, using the circuit in (a). 3 4 Passive Components against current through the material, the value of resistance is repre-sented by the slope of the graph. For a material which is kept at a constant temperature, a straight-line graph indicates that the material is ohmic, obeying Ohm's law (Figure 1.1). Non-ohmic behaviour is represented on such a graph by curved lines or lines which do not pass through the point, called the origin, which represents zero voltage and Figure 1.2. Three types of non-ohmic behaviour indicated by graph curves zero current. Non-ohmic behaviour can be caused by temperature changes (light bulbs, thermistors), by voltage-generating effects (thermocouples), or by conductivity being affected by voltage (diodes), as in Figure 1.2. Resistance values on components are either colour coded, as noted in Table 1.2, or have values printed on using the convention of BS 1852: 1970 (Table 1.3). Resistivity The resistance of any sample of material is determined by its dimensions and by the value of resistivity of the material. Wire drawn from a single reel will have a resistance value depending on the length cut; for example, a 3 m length will have three times the resistance of a 1 m length. When equal lengths of wire of the same material are compared, the resistance multiplied by the square of the diameter is the same for each.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter 3 Resistor A typical axial-lead resistor Partially exposed Tesla TR-212 1 kΩ carbon film resistor ____________________ WORLD TECHNOLOGIES ____________________ Axial-lead Resistors on tape. The tape is removed during assembly before the leads are formed and the part is inserted into the board. Three carbon composition Resistors in a 1960s valve (vacuum tube) radio ____________________ WORLD TECHNOLOGIES ____________________ A resistor is a two-terminal passive electronic component which implements electrical resistance as a circuit element. When a voltage V is applied across the terminals of a resistor, a current I will flow through the resistor in direct proportion to that voltage. The reciprocal of the constant of proportionality is known as the resistance R, since, with a given voltage V, a larger value of R further resists the flow of current I as given by Ohm's law: Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in most electronic equipment. Practical Resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel-chrome). Resistors are also implemented within integrated circuits, particularly analog devices, and can also be integrated into hybrid and printed circuits. The electrical functionality of a resistor is specified by its resistance: common commercial Resistors are manufactured over a range of more than 9 orders of magnitude. When specifying that resistance in an electronic design, the required precision of the resistance may require attention to the manufacturing tolerance of the chosen resistor, according to its specific application. The temperature coefficient of the resistance may also be of concern in some precision applications.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter-6 Resistor A typical axial-lead resistor ____________________ WORLD TECHNOLOGIES ____________________ Partially exposed Tesla TR-212 1 kΩ carbon film resistor Axial-lead Resistors on tape. The tape is removed during assembly before the leads are formed and the part is inserted into the board. ____________________ WORLD TECHNOLOGIES ____________________ Three carbon composition Resistors in a 1960s valve (vacuum tube) radio A resistor is a two-terminal passive electronic component which implements electrical resistance as a circuit element. When a voltage V is applied across the terminals of a resistor, a current I will flow through the resistor in direct proportion to that voltage. The reciprocal of the constant of proportionality is known as the resistance R, since, with a given voltage V, a larger value of R further resists the flow of current I as given by Ohm's law: Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in most electronic equipment. Practical Resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel-chrome). Resistors are also implemented within integrated circuits, particularly analog devices, and can also be integrated into hybrid and printed circuits. The electrical functionality of a resistor is specified by its resistance: common com-mercial Resistors are manufactured over a range of more than 9 orders of magnitude. When specifying that resistance in an electronic design, the required precision of the resistance may require attention to the manufacturing tolerance of the chosen resistor, according to its specific application. The temperature coefficient of the resistance may also be of concern in some precision applications.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- The English Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 1 Resistor A typical axial-lead resistor ________________________ WORLD TECHNOLOGIES ________________________ Partially exposed Tesla TR-212 1 kΩ carbon film resistor Axial-lead Resistors on tape. The tape is removed during assembly before the leads are formed and the part is inserted into the board. ________________________ WORLD TECHNOLOGIES ________________________ Three carbon composition Resistors in a 1960s valve (vacuum tube) radio A resistor is a two-terminal electronic component that produces a voltage across its terminals that is proportional to the electric current through it in accordance with Ohm's law: V = IR Resistors are elements of electrical networks and electronic circuits and are ubiquitous in most electronic equipment. Practical Resistors can be made of various compounds and films, as well as resistance wire (wire made of a high -resistivity alloy, such as nickel-chrome). The primary characteristics of a resistor are the resistance, the tolerance, the maximum working voltage and the power rating. Other characteristics include temperature coe-fficient, noise, and inductance. Less well-known is critical resistance, the value below which power dis sipation limits the maximum permitted current, and above which the limit is applied voltage. Critical resistance is determined by the design, materials and dimensions of the resistor. Resistors can be integrated into hybrid and printed circuits, as well as integrated circuits. Size, and position of leads (or terminals), are relevant to equipment designers; Resistors must be physically large enough not to overheat when dissipating their power. ________________________ WORLD TECHNOLOGIES ________________________ Units The ohm (symbol: Ω) is the SI unit of electrical resistan ce, named after Georg Simon Ohm.
- Dennis L. Eggleston(Author)
- 2011(Publication Date)
- Cambridge University Press(Publisher)
1 Basic concepts and resistor circuits 1.1 Basics We start our study of electronics with definitions and the basic laws that apply to all circuits. This is followed by an introduction to our first circuit element – the resistor. In electronics, we are interested in keeping track of two basic quantities: the currents and voltages in a circuit. If you can make these quantities behave like you want, you have succeeded. Current measures the flow of charge past a point in the circuit. The units of current are thus coulombs per second or amperes , abbreviated as A. In this text we will use the symbol I or i for current. As charges move in circuits, they undergo collisions with atoms and lose some of their energy. It thus takes some work to move charges around a circuit. The work per unit charge required to move some charge between two points is called the voltage between those points. (In physics, this work per unit charge is equivalent to the difference in electrostatic potential between the two points, so the term potential difference is sometimes used for voltage.) The units of voltage are thus joules per coulomb or volts , abbreviated V. In this text we will use the symbol V or v for voltage. In a circuit, there are sources and sinks of energy. Some sources of energy (or voltage) include batteries (which convert chemical energy to electrical energy), gen-erators (mechanical to electrical energy), solar cells (radiant to electrical energy), and power supplies and signal generators (electrical to electrical energy). All other electrical components are sinks of energy. Let’s see how this works. The simplest circuit will involve one voltage source and one sink, with connecting wires as shown in Fig. 1.1 . By convention, we denote the two sides of the voltage source as + and − . A positive charge moving from the − side to the + side of the source gains energy. Thus we say that the voltage across the source is positive.
eBook - PDFFirst and Second Order Circuits and Equations
Technical Background and Insights
- Robert O'Rourke(Author)
- 2024(Publication Date)
- Wiley-IEEE Press(Publisher)
1.3 Ohm’s Law, Resistance, and Resistors 1.3.1 Resistor and Conductor Equations 1.3.1.1 Resistors Figure 1.17 Resistor schematic symbol. A resistor, shown in Figure 1.17, is a circuit element which resists the flow of electrical current. An applied voltage is required in order to pass current through a resistor. The resistance R is the ratio of the voltage applied to the current that flows through the resistor. This ratio relationship is called Ohm’s law. The unit of resistance is the ohm (Ω). 1.3.1.2 Ohm’s Law Current through the resistor I Resistor V Voltage across resistor Figure 1.18 Resistor schematic symbol labeled with passive sign convention for visualizing Ohm’s law. Ohm’s law states that the voltage across a resistor, shown in Figure 1.18, equals the current through the resistor times the resistance R of the resistor. Equivalently, Ohm’s law states that the current through the resistor equals the voltage across the resistor divided by the resistance R. V = IR (1.3) IG = V R = GV (1.4) R = V I (1.5) Equations 1.3, 1.4, and 1.5 are all statements of Ohm’s law, which describes the behavior of a resistor. V is the voltage across the resistor. I is the current through the resistor. R is the resistance and G is conductance, the inverse of resistance, shown in Equation 1.6. The unit of conductance is the siemen. It used to be called the mho. Ohm’s law assumes that the resistor is linear, that is, that the resis- tance of the resistor does not vary as a function of time, current, or voltage. G = 1 R = I V (1.6) 1.3.1.3 Ohm’s Law Notation with Time-Dependent Functions Ohm’s law is also valid for currents and voltages that vary as a function of time. (But the resistance is still constant with respect to time, voltage, and current.) 1.3 Ohm’s Law, Resistance, and Resistors 9 v = iR = f (t) = Ri(t) (1.7) i = v R = f (t) = 1 R v(t) (1.8) The notation v = iR makes no indi- cation of time; it applies to DC.
eBook - PDF- J. David Irwin, R. Mark Nelms(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
C H A P T E R 2 2 2.1 ❯ Ohm’s Law Ohm’s law is named for the German physicist Georg Simon Ohm, who is credited with establishing the voltage–current relationship for resistance. As a result of his pioneering work, the unit of resistance bears his name. Ohm’s law states that the voltage across a resistance is directly proportional to the current flowing through it. The resistance, measured in ohms, is the constant of proportionality be- tween the voltage and current. A circuit element whose electrical characteristic is primarily resistive is called a resistor and is represented by the symbol shown in Fig. 2.1a. A resistor is a physical device that can be purchased in certain standard values in an electronic parts store. These Resistors, which find use in a variety of electrical applications, are normally carbon composition or wirewound. In addition, Resistors can be fabricated using thick oxide or thin metal films for use in hybrid circuits, or they can be diffused in semiconductor integrated circuits. Some typical discrete Resistors are shown in Fig. 2.1b. The mathematical relationship of Ohm’s law is illustrated by the equation υ (t) = Ri (t), where R ≧ 0 (2.1) or, equivalently, by the voltage–current characteristic shown in Fig. 2.2a. Note carefully the re- lationship between the polarity of the voltage and the direction of the current (see HINT 2.1). In addition, note that we have tacitly assumed that the resistor has a constant value and there- fore that the voltage–current characteristic is linear. The symbol Ω is used to represent ohms, and therefore, 1 Ω = 1 V/A HINT 2.1 The passive sign convention will be employed in conjunc- tion with Ohm’s law. Resistive Circuits LEARNING OBJECTIVES The learning goals for this chapter are that students should be able to: ❯ Use Ohm’s law to calculate the voltages and currents in electric circuits. ❯ Apply Kirchhoff’s current law and Kirchhoff’s voltage law to determine the voltages and currents in an electric circuit.
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