Download Understanding DC Circuits: Components, Laws, and Semiconductors and more Slides Chemical Instrumentation and Analysis in PDF only on Docsity! • Electrical Components and Circuits • The purpose of this chapter is to discuss basic direct current (dc) circuit components in preparation for the two following chapters that deal with integrated circuits and microcomputers in instruments for chemical analysis. docsity.com 2A DIRECT CURRENT CIRCUITS AND MEASUREMENTS • Some basic direct current circuits and how they are used in making current, voltage, and resistance measurements will be considered. • The general definition of a circuit is a closed path that may be followed by an electric current. docsity.com The power law states that the power in watts dissipated in a resistive element is given by the product of the current in amperes and the potential difference across the resistance in volts: • P = IV • And substituting Ohm’s law gives: • P = I2R = V2/R docsity.com Basic Direct Current Circuits • Two types of basic dc circuits will be described; series resistive circuits and parallel resistive circuits. docsity.com Series Circuits • Figure 2-1 shows a basic series circuit, which consists of a battery, a switch, and three resistors in series. • Figure 2-1 (Principles of Instrumental Analysis) • The current is the same at all points in a series circuit, that is: • I = I1 = I2 = I3 = I4 docsity.com Applying Kirchhoff’s voltage law to this circuit gives three independent equations. • V = I1R1 • V = I2R2 • V = I3R3 docsity.com Substitution and division by V gives: • 1/ Rp = 1/R1 + 1/R2 + 1/R3 • Since the conductance, G, of a resistor, R, is given by G = 1/R: • Gp = G1 + G2 + G3 • Conductances are additive in a parallel circuit rather than the resistance. docsity.com • In conclusion, the most important things to remember about the differences between resistors in series and parallel are as follows: • Resistors in series have the same current and • Resistors in parallel have the same voltage. docsity.com • Because there is a separation of charge across the depletion region, a potential difference develops across the region that causes a migration of holes and electrons in the opposite direction. The current that results from the diffusion of holes and electrons is balanced by the current produced by migration of the carriers in the electric field, thus there is no net current. The magnitude of potential difference across the depleted region depends upon the composition of the materials used in the pn junction. docsity.com Transistors • The transistor is the basic semiconductor amplifying and switching device. This device provides an output signal whose magnitude is significantly greater than the signal at the input. Several types of transistors are available. Two of the most widely used are: bipolar junction transistor and the field effect transistor. docsity.com 2C READOUT DEVICES • The oscilloscope is a most useful and versatile laboratory instrument that utilizes a cathode-ray tube as a readout device. Both analog and digital oscilloscopes are manufactured. Digital oscilloscopes are used when sophisticated signal processing is required. Analog oscilloscopes are generally simpler than their digital counterparts, are usually portable, easier to use, and less expensive. docsity.com
