Physics
Current-Voltage Characteristics
Current-voltage characteristics refer to the relationship between the current flowing through a material or device and the voltage applied across it. This relationship is often represented graphically, showing how the current changes with varying voltage. Understanding these characteristics is crucial for analyzing the behavior of electronic components and materials, and for designing and optimizing electronic circuits.
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4 Key excerpts on "Current-Voltage Characteristics"
eBook - ePub- Dale Patrick, Stephen Fardo(Authors)
- 1999(Publication Date)
- Newnes(Publisher)
A source such as a battery or generator produces current flow through a circuit. As voltage is increased, the amount of current in a circuit also is increased. Voltage is also called electromotive force (EMF). This term is largely responsible for the usage of E as an identifying letter for voltage. With the development of solid-state electronics the letter E has other meanings. To avoid duplications the letter V is now being used to identify voltage. Resistance The opposition to current flow in electric circuits is called resistance. Resistance is not the same for all materials. The number of free electrons in a material determines the amount of opposition to current flow. Atoms of some materials give up their free electrons easily. These materials offer low opposition to current flow. Other materials hold their outer electrons and offer high opposition to current flow. Electric current is the movement of free electrons in a material. Electric current needs a source of electric pressure to move the free electrons through a material. Electric current does not flow if the source of electric pressure is removed. A material does not release electrons until enough force is applied. With a constant amount of electric force (voltage) and more opposition (resistance) to current flow, the number of electrons flowing (current) through the material is smaller. With constant voltage, current flow is increased by means of decreasing resistance. Decreased current results from more resistance. By increasing or decreasing the amount of resistance in a circuit, one can change the amount of current flow. Materials that are good conductors have many free electrons. Insulating materials do not easily give up the electrons in the outer orbits of their atoms. Metals are the best conductors, copper, aluminum, and iron wire being the most common. Carbon and water are two nonmetal conductors
- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2023(Publication Date)
- Wiley(Publisher)
Current can exist in this device only when the polarity of V is positive and the applied poten- tial difference is more than about 1.5 V. When current does exist, the relation between i and V is not linear; it depends on the value of the applied potential difference V. We distinguish between the two types of device by saying that one obeys Ohm’s law and the other does not. +2 0 –2 Current (mA) Potential difference (V) –2 0 +2 +4 +4 +2 0 –2 Current (mA) –4 –2 0 +2 +4 ( a) ( b ) ( c ) V ? i + – i Potential difference (V) –4 FIGURE 26.4.1 (a) A potential differ- ence V is applied to the terminals of a device, establishing a current i. (b) A plot of current i versus applied potential difference V when the device is a 1000 Ω resistor. (c) A plot when the device is a semiconducting pn junction diode. (This assertion is correct only in certain situations; still, for historical reasons, the term “law” is used.) The device of Fig. 26.4.1b—which turns out to be a 1000 Ω resistor—obeys Ohm’s law. The device of Fig. 26.4.1c—which is called a pn junc- tion diode—does not. It is often contended that V = iR is a statement of Ohm’s law. That is not true! This equation is the defining equation for resistance, and it applies to all conducting devices, whether they obey Ohm’s law or not. If we measure the potential difference V across, and the current i through, any device, even a pn junction diode, we can find its resistance at that value of V as R = V/i. The essence of Ohm’s law, however, is that a plot of i versus V is linear; that is, R is independent of V. We can generalize this for conducting materials by using Eq. 26.3.4 ( E → = ρ J → ): All homogeneous materials, whether they are conductors like copper or semi- conductors like pure silicon or silicon containing special impurities, obey Ohm’s law within some range of values of the electric field. If the field is too strong, however, there are departures from Ohm’s law in all cases.
- Miguel F. Acevedo(Author)
- 2018(Publication Date)
- CRC Press(Publisher)
3 Fundamentals of Direct Current Electric CircuitsThis chapter is one of several providing a very basic review of those major concepts of electrical circuits that we need in order to understand electrical power systems. In this chapter, we review basic electrical quantities and circuits, introducing Ohm’s law and the fundamentals of circuit analysis methods including Kirchhoff’s voltage and current laws, nodal and mesh analysis, and Thévenin and Norton theorems. In preparation for understanding power transfer, we cover modeling of voltage and current sources and the basics of maximum power transfer. In this chapter, we will focus on direct current (DC) circuits, and later, in Chapter 5 , we introduce alternating current (AC) circuits. This topic is expanded in Chapter 8 discussing AC circuit analysis and power calculation for AC circuits, and in Chapter 10 when we introduce transformers and three-phase circuits. Basic DC circuit analysis is covered in many textbooks used in introductory circuit analysis courses and can serve as supplementary material [1–3 ]. Reviews are also available in textbooks devoted to renewable energy [4 ,5 ].3.1 Basics of Electric Circuits3.1.1 Principles of Electrical QuantitiesElectrical charge is a fundamental property of matter that can both generate and interact with electromagnetic fields. Charge can be positive or negative; at the subatomic level, protons represent positive charge, whereas electrons have negative charge. The unit of charge is the coulomb or C, where 1 C is the equivalent charge of 6.2 × 1018 electrons. In a conductor, free electrons can flow and represent a movement of negative charge.Voltage is the potential energy difference between two points in an electric field, measured per unit charge. Being potential energy means it is available to perform the work of moving a unit charge against an electric field. Intuitively, voltage is the energy available to cause electrons to flow through a conductor. Its unit is volt or V, which is defined as joule/coulomb (J/C), and is named volt in honor of Alessandro Volta. In general, work and charge vary with time. Denoting charge by q , voltage by v , and work by w
eBook - PDF- David Halliday, Robert Resnick, Jearl Walker(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
+2 0 –2 Current (mA) Potential difference (V) –2 0 +2 +4 +4 +2 0 –2 Current (mA) –4 –2 0 +2 +4 ( a) ( b ) ( c ) V ? i + – i Potential difference (V) –4 Figure 26.4.1 (a) A potential differ- ence V is applied to the terminals of a device, establishing a current i. (b) A plot of current i versus applied potential difference V when the device is a 1000 Ω resistor. (c) A plot when the device is a semiconducting pn junction diode. (This assertion is correct only in certain situations; still, for historical reasons, the term “law” is used.) The device of Fig. 26.4.1b—which turns out to be a 1000 Ω resistor—obeys Ohm’s law. The device of Fig. 26.4.1c—which is called a pn junc- tion diode—does not. It is often contended that V = iR is a statement of Ohm’s law. That is not true! This equation is the defining equation for resistance, and it applies to all conducting devices, whether they obey Ohm’s law or not. If we measure the potential difference V across, and the current i through, any device, even a pn junction diode, we can find its resistance at that value of V as R = V/i. The essence of Ohm’s law, however, is that a plot of i versus V is linear; that is, R is independent of V. We can generalize this for conducting materials by using Eq. 26.3.4 ( E → = ρ J → ): All homogeneous materials, whether they are conductors like copper or semi- conductors like pure silicon or silicon containing special impurities, obey Ohm’s law within some range of values of the electric field. If the field is too strong, however, there are departures from Ohm’s law in all cases. Ohm’s law is an assertion that the current through a device is always directly proportional to the potential difference applied to the device. A conducting device obeys Ohm’s law when the resistance of the device is independent of the magnitude and polarity of the applied potential difference.
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