Physics
Capacitor Discharge
Capacitor discharge refers to the process of releasing stored electrical energy from a capacitor. When a capacitor is discharged, the stored charge is released through a circuit, resulting in a flow of current. This discharge can occur rapidly, releasing the stored energy in a short amount of time, and is commonly used in various electronic devices and circuits.
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5 Key excerpts on "Capacitor Discharge"
eBook - ePub- Yuri P. Raizer, Mikhail N. Shneider, Nikolai A. Yatsenko(Authors)
- 2017(Publication Date)
- CRC Press(Publisher)
1Basic Principles of the RF Capacitive Discharge
This chapter is an introduction to the physics of radio-frequency (RF) capacitive discharges. It describes various techniques for the excitation of RF field in a gas and the behavior of electrons (the majority charge carriers in fast oscillating electric fields), the electrodynamic characteristics of discharge plasma and their influence on an oscillating field. The production and loss of electrons and the plasma maintenance are discussed briefly. Basic data on the structure and behavior of RF discharges are given, and the formation of space charge sheaths at the electrodes and of constant potential in RF plasma is explained. A simplified RF discharge model is analyzed in order to provide a basis for further discussion of experimental data. Evidently, one cannot do an experiment and understand the results obtained without a simplified initial model of the phenomenon under study. The model will also serve as a starting point for consideration of the details of more complicated theories.1.1 Excitation of an RF discharge
The RF range commonly used in discharge practice isf = ω / 2 π ≃ 1 − 100MHz. RF discharges can be subdivided into inductive and capacitive discharges differing in the way an RF field is induced in the discharge space. Inductive methods are based on electromagnetic induction so that the created electric field is a vortex field with closed lines of force. In capacitive methods, the voltage from an RF generator is applied to the electrodes, the lines of force strike them and the resultant field is essentially a potential field.A simple and commonly used schematic representation of the inductive discharge is shown in Figure 1.1(a)
eBook - PDF- William Moebs, Samuel J. Ling, Jeff Sanny(Authors)
- 2016(Publication Date)
- Openstax(Publisher)
Chapter 8 | Capacitance 361 Figure 8.15 The capacitors on the circuit board for an electronic device follow a labeling convention that identifies each one with a code that begins with the letter “C.” The energy U C stored in a capacitor is electrostatic potential energy and is thus related to the charge Q and voltage V between the capacitor plates. A charged capacitor stores energy in the electrical field between its plates. As the capacitor is being charged, the electrical field builds up. When a charged capacitor is disconnected from a battery, its energy remains in the field in the space between its plates. To gain insight into how this energy may be expressed (in terms of Q and V), consider a charged, empty, parallel-plate capacitor; that is, a capacitor without a dielectric but with a vacuum between its plates. The space between its plates has a volume Ad, and it is filled with a uniform electrostatic field E. The total energy U C of the capacitor is contained within this space. The energy density u E in this space is simply U C divided by the volume Ad. If we know the energy density, the energy can be found as U C = u E ( Ad) . We will learn in Electromagnetic Waves (after completing the study of Maxwell’s equations) that the energy density u E in a region of free space occupied by an electrical field E depends only on the magnitude of the field and is (8.9) u E = 1 2 ε 0 E 2 . If we multiply the energy density by the volume between the plates, we obtain the amount of energy stored between the plates of a parallel-plate capacitor: U C = u E ( Ad) = 1 2 ε 0 E 2 Ad = 1 2 ε 0 V 2 d 2 Ad = 1 2 V 2 ε 0 A d = 1 2 V 2 C . In this derivation, we used the fact that the electrical field between the plates is uniform so that E = V /d and C = ε 0 A/d. Because C = Q/V , we can express this result in other equivalent forms: (8.10) U C = 1 2 V 2 C = 1 2 Q 2 C = 1 2 QV .
eBook - PDF- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
25.4.3 For a capacitor, apply the relationship between the potential energy, the internal volume, and the internal energy density. 25.4.4 For any electric field, apply the relationship between the potential energy density u in the field and the field’s magnitude E. 25.4.5 Explain the danger of sparks in airborne dust. Figure 25.3.4 A potential difference V 0 is applied to capacitor 1 and the charging battery is removed. Switch S is then closed so that the charge on capacitor 1 is shared with capacitor 2. S C 2 C 1 q 0 After the switch is closed, charge is transferred until the potential differences match. Additional examples, video, and practice available at WileyPLUS 771 25.4 ENERGY STORED IN AN ELECTRIC FIELD Key Ideas ● The electric potential energy U of a charged capacitor, U = q 2 ___ 2c = 1 _ 2 CV 2 , is equal to the work required to charge the capacitor. This energy can be associated with the capacitor’s electric field E → . ● Every electric field, in a capacitor or from any other source, has an associated stored energy. In vacuum, the energy density u (potential energy per unit volume) in a field of magnitude E is u = 1 _ 2 ε 0 E 2 . Energy Stored in an Electric Field Work must be done by an external agent to charge a capacitor. We can imagine doing the work ourselves by transferring electrons from one plate to the other, one by one. As the charges build, so does the electric field between the plates, which opposes the continued transfer. So, greater amounts of work are required. Actually, a battery does all this for us, at the expense of its stored chemical energy. We visual- ize the work as being stored as electric potential energy in the electric field between the plates. Suppose that, at a given instant, a charge q′ has been transferred from one plate of a capacitor to the other. The potential difference V′ between the plates at that instant will be q′/C.
- 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)
When we close the switch, completing the circuit, electrons are driven through the wires by an electric field that the battery sets up in the wires. The field drives electrons from capacitor plate h to the positive terminal of the battery; thus, plate h, losing electrons, becomes positively charged. The field drives just as many electrons from the negative terminal of the battery to capacitor plate l; thus, plate l, gaining electrons, becomes negatively charged just as much as plate h, losing electrons, becomes positively charged. Initially, when the plates are uncharged, the potential difference between them is zero. As the plates become oppositely charged, that potential difference increases until it equals the potential difference V between the terminals of the battery. Then plate h and the positive terminal of the battery are at the same potential, and there is no longer an electric field in the wire between them. Similarly, plate l and the negative terminal reach the same potential, and there is then no electric field in the wire between them. Thus, with the field zero, there is no further drive of electrons. The capacitor is then said to be fully charged, with a potential difference V and charge q that are related by q = CV. In this book we assume that during the charging of a capacitor and afterward, charge cannot pass from one plate to the other across the gap separating them. Also, we assume that a capacitor can retain (or store) charge indefinitely, until it is put into a circuit where it can be discharged. The symbol V and potential difference Recall that in previous chapters, the symbol V represents an electric potential at a point or along an equipotential surface. However, in matters concerning electrical devices, V often represents a potential difference between two points or two equipotential surfaces. In this chapter and in later ones, you will see a mixture of the two meanings of V and thus you will need to be alert as to the intent of the symbol.
eBook - PDF- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
Thus, the capacitors in Fig. 25-11 are not connected in series; and although they are drawn parallel, in this situation they are not in parallel. 630 CHAPTER 25 CAPACITANCE Energy Stored in an Electric Field Work must be done by an external agent to charge a capacitor. We can imagine doing the work ourselves by transferring electrons from one plate to the other, one by one. As the charges build, so does the electric field between the plates, which opposes the continued transfer. So, greater amounts of work are required. Actually, a battery does all this for us, at the expense of its stored chemical energy. We visualize the work as being stored as electric potential energy in the electric field between the plates. Additional examples, video, and practice available at WileyPLUS 25-4 ENERGY STORED IN AN ELECTRIC FIELD Learning Objectives After reading this module, you should be able to . . . 25.16 Explain how the work required to charge a capaci- tor results in the potential energy of the capacitor. 25.17 For a capacitor, apply the relationship between the potential energy U, the capacitance C, and the poten- tial difference V. 25.18 For a capacitor, apply the relationship between the potential energy, the internal volume, and the internal energy density. 25.19 For any electric field, apply the relationship between the potential energy density u in the field and the field’s magnitude E. 25.20 Explain the danger of sparks in airborne dust. Key Ideas ● The electric potential energy U of a charged capacitor, U = q 2 2c = 1 2 CV 2 , is equal to the work required to charge the capacitor. This energy can be associated with the capacitor’s electric field E → . ● Every electric field, in a capacitor or from any other source, has an associated stored energy. In vacuum, the energy density u (potential energy per unit volume) in a field of magnitude E is u = 1 2 ε 0 E 2 . is no electric field within the connecting wires to move con- duction electrons.
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