Standard Capacitor Values

12 Key excerpts on "Standard Capacitor Values"

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  eBook - PDF

  Fundamentals of Physics, Extended

  • David Halliday, Robert Resnick, Jearl Walker(Authors)
  • 2018(Publication Date)
  • Wiley

    (Publisher)

  717 C H A P T E R 2 5 Capacitance What Is Physics? One goal of physics is to provide the basic science for practical devices designed by engineers. The focus of this chapter is on one extremely common example—the capacitor, a device in which electrical energy can be stored. For example, the batteries in a camera store energy in the photoflash unit by charg- ing a capacitor. The batteries can supply energy at only a modest rate, too slowly for the photoflash unit to emit a flash of light. However, once the capacitor is charged, it can supply energy at a much greater rate when the photoflash unit is triggered—enough energy to allow the unit to emit a burst of bright light. The physics of capacitors can be generalized to other devices and to any situ- ation involving electric fields. For example, Earth’s atmospheric electric field is modeled by meteorologists as being produced by a huge spherical capacitor that partially discharges via lightning. The charge that skis collect as they slide along snow can be modeled as being stored in a capacitor that frequently discharges as sparks (which can be seen by nighttime skiers on dry snow). The first step in our discussion of capacitors is to determine how much charge can be stored. This “how much” is called capacitance. Capacitance Figure 25-1 shows some of the many sizes and shapes of capacitors. Figure 25-2 shows the basic elements of any capacitor — two isolated conductors of any 25-1 CAPACITANCE Learning Objectives After reading this module, you should be able to . . . 25.01 Sketch a schematic diagram of a circuit with a parallel-plate capacitor, a battery, and an open or closed switch. 25.02 In a circuit with a battery, an open switch, and an uncharged capacitor, explain what happens to the conduction electrons when the switch is closed.

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  Halliday and Resnick's Principles of Physics

  • David Halliday, Robert Resnick, Jearl Walker(Authors)
  • 2020(Publication Date)
  • Wiley

    (Publisher)

  C H A P T E R 2 5 Capacitance What Is Physics? One goal of physics is to provide the basic science for practical devices designed by engineers. The focus of this chapter is on one extremely common example—the capacitor, a device in which electrical energy can be stored. For example, the batteries in a camera store energy in the photoflash unit by charging a capacitor. The batteries can supply energy at only a modest rate, too slowly for the photoflash unit to emit a flash of light. However, once the capaci- tor is charged, it can supply energy at a much greater rate when the photoflash unit is triggered—enough energy to allow the unit to emit a burst of bright light. The physics of capacitors can be generalized to other devices and to any sit- uation involving electric fields. For example, Earth’s atmospheric electric field is modeled by meteorologists as being produced by a huge spherical capacitor that partially discharges via lightning. The charge that skis collect as they slide along snow can be modeled as being stored in a capacitor that frequently dis- charges as sparks (which can be seen by nighttime skiers on dry snow). The first step in our discussion of capacitors is to determine how much charge can be stored. This “how much” is called capacitance. Capacitance Figure 25-1 shows some of the many sizes and shapes of capacitors. Figure 25-2 shows the basic elements of any capacitor — two isolated conductors 25-1 CAPACITANCE Learning Objectives After reading this module, you should be able to . . . 25.01 Sketch a schematic diagram of a circuit with a parallel-plate capacitor, a battery, and an open or closed switch. 25.02 In a circuit with a battery, an open switch, and an uncharged capacitor, explain what happens to the conduction electrons when the switch is closed.

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  eBook - ePub

  Measurement, Instrumentation, and Sensors Handbook

  Electromagnetic, Optical, Radiation, Chemical, and Biomedical Measurement

  • John G. Webster, Halit Eren, John G. Webster, Halit Eren(Authors)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  Table 28.6 . Nevertheless, tolerances of precision capacitors are much tighter—in the range of 0.25%, 0.5%, 0.625%, 1%, 2%, and 3% of the rated values. Undoubtedly, these capacitors are much more expensive than the general-purpose range.

  For capacitors in the small pF range, the standard tolerances are ±1.5, ±1, ±0.5, ±0.25, and ±0.1 pF. Usually, low tolerance ranges are achieved by selecting good-quality materials and elaborate manufacturing.

  Standard capacitors are constructed from interleaved metal plates using air as the dielectric material. The area of the plates and distance between them are determined and constructed with precision. National Bureau of Standards maintains a bank of primary standard air capacitors that can be used to calibrate the secondary and working standards in laboratory and industrial application. The working standards of small capacitances are obtained by using air capacitors, whereas working standards of larger capacitances are made from solid dielectric materials. Usually, silver-mica capacitors are selected as working standards since they are very stable, exhibit low dissipation factors and small temperature coefficients, and aging effects are excellent. They are available in decade mounted forms with multiplication factors of 10.

  28.5 Capacitors in Circuits

  The capacitor is used as a two-terminal element in electric circuits with the current–voltage relationship given by

  i ( t ) = C   d v ( t ) d t

  (28.9)

  where C is the capacitance.

  The circuit representation is given in Figure 28.11a .

  From the v (t ), i (t ) relationship, the instantaneous power of this element can then be given by

  p ( t ) = v ( t ) i ( t )

  (28.10)

  The stored energy in the capacitor at time t s can be calculated as

  w ( t ) = ∫ C v ( t ) { d v ( t ) d t } d t = [ C v 2 ( t ) ] 2

  (28.11)

  If the voltage across the capacitor is time varying, the energy stored in the capacitor in a time interval t 1 – t 2 can be calculated from Equation 28.11

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  eBook - PDF

  Fundamentals of Physics, Volume 2

  • David Halliday, Robert Resnick, Jearl Walker(Authors)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  The physics of capacitors can be generalized to other devices and to any situation involving electric fields. For example, Earth’s atmo- spheric electric field is modeled by meteorologists as being produced by a huge spherical capacitor that partially discharges via lightning. The charge that skis collect as they slide along snow can be modeled as being stored in a capacitor that frequently discharges as sparks (which can be seen by nighttime skiers on dry snow). The first step in our discussion of capacitors is to determine how much charge can be stored. This “how much” is called capacitance. Capacitance Figure 25.1.1 shows some of the many sizes and shapes of capacitors. Figure 25.1.2 shows the basic elements of any capacitor—two isolated conductors of any shape. No matter what their geometry, flat or not, we call these conductors plates. Figure 25.1.1 An assortment of capacitors. Paul Silvermann/Fundamental Photographs 760 CHAPTER 25 CAPACITANCE Figure 25.1.3a shows a less general but more conventional arrangement, called a parallel-plate capacitor, consisting of two parallel conducting plates of area A separated by a distance d. The symbol we use to represent a capacitor (⫞⊦) is based on the structure of a parallel-plate capacitor but is used for capacitors of all geometries. We assume for the time being that no material medium (such as glass or plastic) is present in the region between the plates. In Module 25.5, we shall remove this restriction. When a capacitor is charged, its plates have charges of equal magnitudes but opposite signs: +q and –q. However, we refer to the charge of a capacitor as being q, the absolute value of these charges on the plates. (Note that q is not the net charge on the capacitor, which is zero.) Because the plates are conductors, they are equipotential surfaces; all points on a plate are at the same electric potential. Moreover, there is a potential dif- ference between the two plates.

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  eBook - ePub

  Electrochemical Supercapacitors for Energy Storage and Delivery

  Fundamentals and Applications

  • Aiping Yu, Victor Chabot, Jiujun Zhang(Authors)
  • 2017(Publication Date)
  • CRC Press

    (Publisher)

  Figure 1.1a . This structural change was very important after both world wars when demands for electronic parts increased. Capacitors were used in complex electronic systems, resulting in greater production and standardization programs to ensure the reliability and quality of the capacitors. Significant effort to meet quality and reliability requirements contributed to the successful improvements of modern electronics. Smaller and lighter capacitors possess greater capabilities and stability in adverse conditions and over wide temperature ranges.

  FIGURE 1.1(See color insert.) (a) Simplified schematic of capacitor design. (b) Cross-sectional schematic of Leyden jar (water-filled glass jar containing metal foil electrodes on its inner and outer surfaces, (denoted A and B).

  This chapter reviews the fundamentals of capacitors and emphasizes the critical parameters of dielectric materials and the construction of capacitors, as well as their operations in a variety of applications [1 ].

  1.2 Electric Charge, Electric Field, and Electric Potential and Their Implications for Capacitor Cell Voltage

  1.2.1 Electric Charge

  The roles of a capacitor are to separate, store, and deliver electric charges and the concepts and properties of charges must be understood. In general, both positive and negative electric charges exist in all physical objects in the universe whether they are animate or inanimate. A physical object will display a neutral charge when there are equal numbers of positive charges (protons) and negative charges (electrons). However, a net electric charge can occur through unbalancing the charge equilibrium in some areas of an object. Thus some areas will have more negative than positive charges and vice versa.

  In general, two positive charges reciprocally repel each other as do two negative charges; while opposite charges feel mutual attractive forces. Figure 1.2

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  eBook - PDF

  Physics, Volume 2

  • David Halliday, Robert Resnick, Kenneth S. Krane(Authors)
  • 2019(Publication Date)
  • Wiley

    (Publisher)

  CHAPTER 30 679 CHAPTER 30 CAPACITANCE I n many applications of electric circuits, the goal is to store electrical charge or energy in an electrostatic field. A device that stores charge is called a capacitor, and the property that determines how much charge it can store is its capacitance. We shall see that the ca- pacitance depends on the geometrical properties of the device and not on the electric field or the potential. In this chapter we define capacitance and show how to calculate the capacitance of a few simple de- vices and of combinations of capacitors. We study the energy stored in capacitors and show how it is re- lated to the strength of the electric field. Finally, we investigate how the presence of a dielectric in a capaci- tor enhances its ability to store electric charge. 30-1 CAPACITORS A capacitor* is a device that stores energy in an electrosta- tic field. A flashbulb, for example, requires a short burst of electric energy that exceeds what a battery can generally provide. A capacitor can draw energy relatively slowly (over several seconds) from the battery, and it then can re- lease the energy rapidly (within milliseconds) through the bulb. Much larger capacitors are used to produce short laser pulses in attempts to induce thermonuclear fusion in tiny pellets of hydrogen. In this case the power level during the pulse is about 10 14 W, about 200 times the entire electrical generating capacity of the United States, but the pulses typ- ically last only for 10 9 s. Capacitors are also used to produce electric fields, such as the parallel-plate device that gives the very nearly uni- form electric field that deflects beams of electrons in a TV or oscilloscope tube. In circuits, capacitors are often used to smooth out the sudden variations in line voltage that can damage computer memories. In another application, the tuning of a radio or TV receiver is usually done by varying the capacitance of the circuit.

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  eBook - PDF

  Newnes Circuit Calculations Pocket Book

  with Computer Programs

  • Thomas J. Davies(Author)
  • 2016(Publication Date)
  • Newnes

    (Publisher)

  Capacitance is a measure of how much charge can be stored for each volt across the capacitor. Charge Q = CV where Q is in coulombs, C C is in farads, F V is in volts, V Example 7 A 680 pF capacitor has 6 V across the plates. Calculate the charge stored. Q = CV = 680 x 10 12 x 6 = 4.08 x 1 0 -9 C = 4.08 x 10~ 9 x 10 9 nC = 4.08 nC 10 PRINT PROG 73 20 PRINT CAPACITOR CHARGE 30 INPUT ENTER CAPACITANCE IN PICOFARADS ; C 40 INPUT ENTER VOLTAGE IN VOLTS ; V 50 LET C=C/10*12 60 LET Q=C*V 70 PRINT CHARGE = Q*10*9 NANOCOULOMDS Example 8 A 0.1 uF capacitor stores a charge of 0.02 x 10 3 C. What is the voltage across the terminals? Capacitors 107 y = Q _ 0-02 x 1Q-3 _ O02 x 10 3 0.1 x 10 = 200 V 0.1 10 PRINT PROG 74 20 PRINT CAPACITOR VOLTAGE 30 INPUT ENTER CAPACITANCE IN MICROFARADS ; C 40 INPUT ENTER CHARGE IN COULOMBS ; Q 50 LET C=C/1CT6 60 LET V=Q/C 70 PRINT VOLTAGE = V VOLTS Example 9 Calculate the value of a capacitor which stores a charge of 2 mC when charged to 400 V. Q 2 x 10~ 3 2 x KT 3 x 10 6 C = — = F = ixF V 400 400 = 5 (JL F 10 PRINT PROG 7 5 20 PRINT CAPACITOR VALUE 30 INPUT ENTER CHARGE IN MILLICOULOMBS ; Q 40 INPUT ENTER VOLTAGE IN VOLTS ; V 50 LET Q=Q/10*3 60 LET C=Q/V 70 PRINT VALUE = C*10*6 MICROFARADS (c) Energy stored When charge is moved into a capacitor work is done, and hence energy is expended. This energy is stored between the plates in the form of an electric field. Energy stored, W = CV 2 where W is in joules, J C is in farads, F V is in volts, V Example 10 Calculate the energy stored in a 0.1 u-F capacitor with an applied voltage of 250 V. W = x 0.1 x 10~ 6 x (250) 2 = 3.125 x KT 3 J = 3.125 x 10 3 x 10 3 = 3.125 mJ 10 PRINT PROG 76 20 PRINT ENERGY STORED 30 INPUT ENTER CAPACITANCE IN MICROFARADS ; C 40 INPUT ENTER VOLTAGE IN VOLTS ; V 50 LET C=C/10*6 60 LET W=.5*C*V*2 70 PRINT ENERGY STORED = WM0~3 MILLIJOULES Example 11 The energy stored in a 0.25 |xF capacitor is 8 x 10 4 J. What is the terminal voltage?

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  eBook - PDF

  Delmar's Standard Textbook of Electricity

  • Stephen Herman(Author)
  • 2019(Publication Date)
  • Cengage Learning EMEA

    (Publisher)

  454 7 AC Circuits Containing Capacitors Sochillplanets/Shutterstock.com SECTION 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. 455 UNIT Why You Need to Know C apacitors are one of the major electric devices. This unit ● explains how capacitors are constructed, how they are charged and discharged, and the differences between different types of capacitors and their markings. ● describes how capacitance is measured and the importance of the voltage rating. ● explains how capacitors store energy in an electrostatic field and how current can flow only when the capacitors are charging or discharging. 19 Capacitors Key Terms Capacitor Dielectric Dielectric constant Dielectric stress Electrolytic Exponential Farad HIPOT JAN (Joint Army-Navy) standard Leakage current Nonpolarized capacitors Plates Polarized capacitors RC time constant Surface area Variable capacitors Outline 19–1 Capacitors 19–2 Electrostatic Charge 19–3 Dielectric Constant 19–4 Capacitor Ratings 19–5 Capacitors Connected in Parallel 19–6 Capacitors Connected in Series 19–7 Capacitive Charge and Discharge Rates 19–8 RC Time Constants 19–9 Applications for Capacitors 19–10 Nonpolarized Capacitors 19–11 Polarized Capacitors 19–12 Variable Capacitors 19–13 Capacitor Markings 19–14 Temperature Coefficients 19–15 Ceramic Capacitors 19–16 Dipped Tantalum Capacitors 19–17 Film Capacitors 19–18 Testing Capacitors Copyright 2020 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part.

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  eBook - PDF

  Halliday's Fundamentals of Physics, 1st Australian & New Zealand Edition

  • David Halliday, Jearl Walker, Patrick Keleher, Paul Lasky, John Long, Judith Dawes, Julius Orwa, Ajay Mahato, Peter Huf, Warren Stannard, Amanda Edgar, Liam Lyons, Dipesh Bhattarai(Authors)
  • 2020(Publication Date)
  • Wiley

    (Publisher)

  The first step in our discussion of capacitors is to determine how much charge can be stored. This ‘how much’ is called capacitance. Capacitance Figure 25.1 shows some of the many sizes and shapes of capacitors. Figure 25.2 shows the basic elements of any capacitor — two isolated conductors of any shape, which, flat or not, are called plates. Figure 25.3 shows two views of a less general but more conventional arrangement, called a parallel‐plate capacitor, consisting of two parallel conducting plates of area A separated by a distance d. Pdf_Folio:547 FIGURE 25.1 An assortment of capacitors. Paul Silvermann / Fundamental Photographs FIGURE 25.2 Two conductors, isolated electrically from each other and from their surroundings, form a capacitor. When the capacitor is charged, the charges on the conductors, or plates as they are called, have the same magnitude q but opposite signs. +q - q FIGURE 25.3 (a) A parallel-plate capacitor, made up of two plates of area A separated by a distance d. The charges on the facing plate surfaces have the same magnitude q but opposite signs. (b) As the feld lines show, the electric feld due to the charged plates is uniform in the central region between the plates. The feld is not uniform at the edges of the plates, as indicated by the ‘fringing’ of the feld lines there. Area A V d Top side of bottom plate has charge -q A -q +q (b) (a ) Bottom side of top plate has charge +q Electric field lines We assume for the time being that no material medium (such as glass or plastic) is present in the region between the plates. In module 25.5, we will remove this restriction. When a capacitor is charged, its plates have charges of equal magnitudes but opposite signs: +q and −q. However, we refer to the charge of a capacitor as being q, the absolute value of these charges on the plates.

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  BTEC National Engineering

  • Mike Tooley, Lloyd Dingle(Authors)
  • 2010(Publication Date)
  • Routledge

    (Publisher)

  mA From which i     8 8 10 8 8 3 . . A mA Charge, capacitance and voltage The charge or quantity of electricity that can be stored in the electric field between the capacitor plates is proportional to the applied voltage and the capacitance of the capacitor (see Figure 6.62 ). Thus, Q CV  where Q is the charge (coulombs), C is the capacitance (F) and V is the potential difference (V). Example 6.33 A 10 μF capacitor is charged to a potential of 250V. Determine the charge stored. The charge stored will be given by: Q CV       10 10 250 2 5 6 . mC KEY POINT Charge is the quantity of electricity that can be stored in a capacitor. The charge in a capacitor is directly proportional to the product of the capacitance and the applied potential difference TYK 6.19 Determine the charge in a capacitor of 470 μF when a potential difference of 22 V appears across its plates. T e s t y o u r k n o w l e d g e TYK Electrical and Electronic Principles 491 UNIT 6 Energy storage When charge, Q, is plotted against voltage, V, for a particular value of capacitance, C, it follows the linear law shown in Figure 6.63a. The slope of the line ( Q/V) indicates the capacitance whilst the area below the line (shown as shaded portion in Figure 6.63b) is a measure of the energy stored in the capacitor. The larger this area is the more energy is stored. TYK 6.20 A capacitor of 150 μF is required to store a charge of 400 μC. What voltage should be applied to the capacitor? Supply, V Field lines Capacitance, C Potential difference, V Charge, Q               1 Figure 6.62 Capacitance, charge and voltage Charge, Q High capacitance Low capacitance Voltage, V (a) Slope  Q V C (b) Charge V Voltage Q Energy  1 2 QV Figure 6.63 Charge plotted against voltage for a capacitor In Figure 6.63, the shaded area can be found by considering the area to be a triangle in which the area is the product of half the base and the height.

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  eBook - ePub

  Passive Components for Circuit Design

  • Ian Sinclair(Author)
  • 2000(Publication Date)
  • Newnes

    (Publisher)

  which gives energy in joules when the units of capacitance and voltage are the farad and the volt respectively. For example, a 5000 μF capacitor charged to 400 V will carry a stored energy of:

  250 × 10−6 × (400)2 = 40J

  This is the amount of energy that would be achieved by a power of 40 W acting for 1 s. When a capacitor short circuited, however, this energy can be discharged in a fraction of a second, and any brief release of such a substantial amount of energy can be very destructive. It can also be painful if it discharges across you, and possibly fatal if you take the discharge of a large capacitor through a path that crosses the heart.

  When the voltage across a capacitor is continually varied, the capacitor will be continually charged and discharged, so that there will be a flow of electrons to and from the plates. This flow constitutes a current so that for an applied (sine-wave) alternating voltage there will be an alternating current flowing, and the current will be proportional to the voltage, just as the current through a resistor is proportional to the voltage across it. We can define a quantity called reactance which is analogous to resistance in the formula:

  V = X×I

  Where V and I are AC values. However, the similarity cannot be taken too far. The reactance of a capacitor is not constant, and there is a phase difference of 90° between current and voltage (see Chapter 1 ). We could, in fact, draw up an alternative definition of a capacitor as an electronic device that permits the flow of signal current but not DC, and creates a 90° phase difference between voltage and current, with current leading voltage.

  • When a capacitor is charging or discharging, the current at any instant is proportional to the rate of change of voltage. This means that instantaneous charging or discharging is impossible, since this would require an infinite rate of change of voltage.

  Capacitor construction

  The simplest type of capacitor is the parallel-plate type, using air as its insulation between the plates. If any solid or liquid insulator is placed between the plates, the capacitance of the arrangement is increased, and the factor by which the capacitance is increased is called the relative permittivity of the material between the plates. Figure 4.2 shows the formula which can be used to calculate the capacitance of this arrangement. This uses a quantity called the permittivity of free space

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  eBook - ePub

  College Physics Essentials, Eighth Edition

  Electricity and Magnetism, Optics, Modern Physics (Volume Two)

  • Jerry D. Wilson, Anthony J. Buffa, Bo Lou(Authors)
  • 2019(Publication Date)
  • CRC Press

    (Publisher)

  capacitance :

  Q = C   ⋅   Δ V   or   C = Q Δ V   (definition   of   capacitance)	(16.9)

  SI unit of capacitance is the coulomb per volt (C/V) or the farad (F)

  The coulomb per volt is named the farad after Michael Faraday, a famous physicist of the nineteenth century, thus 1 C/V = 1 F. The farad is a large unit (see Example 16.6), so the microfarad (1 µ F = 10− 6 F), the nanofarad (1 nF = 10− 9 F), and the picofarad (1 pF = 10− 12 F) are commonly used.

  Capacitance represents the charge Q that can be stored per volt . If a capacitor has a large capacitance value, this means it is capable of holding a large charge per volt compared to one of smaller capacitance. Thus if you connect the same battery to two different capacitors, the one with the larger capacitance stores more charge and energy.

  Capacitance depends only on the geometry (size, shape, and spacing) of the plates (and possibly any material between the plates – see Section 16.5) but specifically not the charge on the plates. To understand this, consider again a set of parallel plates which is now called a parallel plate capacitor. The electric field between the plates given by Equation 16.5:

  E =

  4 π k Q

  A

  The potential difference between the plates can be computed from Equation 16.2 as follows:

  Δ V = E d =

  4 π k Q d

  A

  The capacitance of a parallel plate arrangement is then

  C = Q Δ V = ( 1 4 π k ) A d   ( parallel   plates   only )	(16.10)

  It is common to replace the constants in the parentheses in Equation 16.10 with a single constant called the permittivity of free space ( ε o ) . Knowing k , the permittivity has a value of

  ε o = 1 4 π k = 8.85 × 10 − 12 C 2 N   ⋅   m 2   (permittivity   of free   space )	(16.11)

  ε o

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