2015-03-06 17:24
Introduction A transmission line is a system of conductors connecting one point to another and along which electromagnetic energy can be sent. Thus telephone lines and power distribution li… Read More
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2015-03-06 16:18
Introduction An attenuator is a device for introducing a specified loss between a signal source and a matched load without upsetting the impedance relationship necessary for matching. The l… Read More
2015-03-06 16:16
Introduction to Modulation The transmission of information such as speech, music and data over long distances requires the use of a carrier channel. It is common practise to ‘carry&rs&hell…Read More
2015-03-06 16:15
Introduction A filter is a network designed to pass signals having frequencies within certain bands (called passbands) with little attenuation, but greatly attenuates signals within other b… Read More
2015-03-06 15:40
Introduction Electric fields, magnetic fields and conduction fields (i.e. a region in which an electric current flows) are analogous, i.e. they all exhibit similar characteristics. Thus the… Read More
2015-03-06 15:34
Electric Fields, Capacitance and Permittivity Any region in which an electric charge experiences a force is called an electrostatic field. Electric fields, Coulombs law, capacitance and per… Read More
2015-03-06 15:03
Introduction Many practical waveforms can be represented by simple mathematical expressions, and, by using Fourier series, the magnitude of their harmonic components determined. For wavefor… Read More
2015-03-06 14:55
Maximum Power Transfer Theorems A network that contains linear impedances and one or more voltage or current sources can be reduced to a The´venin equivalent circuit as shown in chapt… Read More
2015-03-06 14:53
Introduction By using Kirchhoff’s laws, mesh-current analysis, nodal analysis or the super- position theorem, currents and voltages in many network can be determined as shown in chapt… Read More
2015-03-06 14:52
Introduction Many of the networks analysed in Chapters 70 to 72 using Kirchhoff’s laws, mesh-current and nodal analysis and the superposition theorem can be analysed more quickly and… Read More
2015-03-06 14:17
Introduction The superposition theorem states: ‘In any network made up of linear impedances and containing more than one source of e.m.f. the resultant current flowing in any branch… Read More
2015-03-06 13:42
Mesh-current Analysis Mesh-current analysis is merely an extension of the use of Kirchhoff’s laws, explained in chapter 70. Figure 71.1 shows a network whose circulating cur- rents I1… Read More
2015-03-06 13:41
Introduction Voltage sources in series-parallel networks cause currents to flow in each branch of the circuit and corresponding volt-drops occur across the circuit components. A.c. circuit… Read More
2015-03-05 17:01
Introduction When a d.c. voltage is applied to a capacitor C and resistor R connected in series, there is a short period of time immediately after the voltage is connected, during which the… Read More
2015-03-05 16:12
Introduction In parallel circuits, such as those shown in Figures 56.1 and 56.2, the voltage is common to each branch of the network and is thus taken as the reference phasor when drawing p… Read More
2015-03-05 16:00
Purely Resistive a.c. Circuit In a purely resistive a.c. circuit, the current IR and applied voltage VR are in phase. See Figure 55.1. Purely Inductive a.c. Circuit In a purely inductive… Read More
2015-03-05 15:56
Introduction The laws that determine the currents and voltage drops in d.c. networks are: (a) Ohm’s law (see chapter 40), (b) the laws for resistors in series and in parallel (see ch… Read More
2015-03-05 15:15
Introduction Electricity is produced by generators at power stations and then distributed by a vast network of transmission lines (called the National Grid system) to industry and for domes… Read More
2015-03-05 14:42
The Bipolar Junction Transistor The bipolar junction transistor consists of three regions of semiconductor material. One type is called a p-n-p transistor, in which two regions of p-type ma… Read More
2015-03-05 13:29
Introduction Tests and measurements are important in designing, evaluating, maintaining and servicing electrical circuits and equipment. In order to detect electrical quantities such as cur… Read More
2015-03-05 13:22
Types of Materials Materials may be classified as conductors, semiconductors or insulators. The classification depends on the value of resistivity of the material. Good conductors are usual… Read More
2015-03-04 17:22
Introduction When the interaction between two loops of a circuit takes place through a magnetic field instead of through common elements, the loops are said to be inductively or magneticall… Read More
2015-03-04 16:56
Introduction to Electromagnetic Induction When a conductor is moved across a magnetic field so as to cut through the lines of force (or flux), an electromotive force (e.m.f.) is produced in… Read More
2015-03-04 16:50
Magnetic Field due to an Electric Current Magnetic fields can be set up not only by permanent magnets, as shown in chapter 45, but also by electric currents. Let a piece of wire be arrange… Read More
2015-03-04 16:34
Magnetic Properties of Materials The full theory of magnetism is one of the most complex of subjects. How- ever the phenomenon may be satisfactorily explained by the use of a simple model… Read More
2006-06-07 11:16
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2006-06-07 11:16
The social impact of computers Many businesses make use of electronic mail and electronic funds transfer to improve efficiency, reduce costs and speed up communication. (a) State one adva… Read More
2006-06-07 11:16
Communications Systems and Word Processing (a) Name a teletext service that is available through an ordinary television signal. (b) Name a widely used public View data service that uses t… Read More
2006-06-07 11:16
Use of Computers in industrial processes A greenhouse has a window which can be opened or closed under computer control. It also has a heater which can be switched on or off by the computer… Read More
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