Permanent magnetic materials

In a permanent magnet a material is used that exhibits magnetism even in the absence of a current-carrying coil. The silicon-iron and nickel-iron alloys are ‘soft’ magnetic materials and possess high permeability & have low hysteresis loss. The converse characteristics are necessary in the ‘hard’ materials that are used for making permanent magnets. In permanent magnets, high remanent flux density & high coercive force, after magnetization to saturation, are often required for the purpose of resisting de-magnetization. The hysteresis loop should be able to embrace the maximum possible area.

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Waveform harmonics

•         Consider that an instantaneous voltage v be represented by  the formula

v = Vm sin 2πft volts.

This is a waveform which varies sinusoidally with time t, has a frequency f, and a maximum value represented by Vm. It is normally assumed that alternating voltages have wave shapes which are sinusoidal where only 1 frequency is present. If the waveform is not happened to be sinusoidal it is called a complex wave, & whatever its shape is, itmay be split up mathematically into components called the fundamental and a number of harmonics.This process is referred to as harmonic analysis.The fundamental, which is the first harmonic, is sinusoidal and has the supply frequency, f ; the other harmonics are also sine waves having frequencies which are integer multiples of f . Thus, if supply frequency is fifty hertz, then the third harmonic frequency is 150Hz, the fifth 250Hz, & so on.

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The LR–CR parallel network

A more all-purpose network containing a coil of inductance “L” and resistance RL connected in parallel with a capacitance C & resistance RC in series is presented in diagram 29.4 below.

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Temperature coefficient of resistance

It is normal when the temperature of a material increases, the resistance increases in the most of conductors, insulators decrease in resistance, whilst the resistance of some special alloys remains almost constant.

The temperature coefficient of resistance of a material is the increase in the resistance of a 1OHM resistor of that material when it is subjected to a rise of temperature of 1◦C. Greek alpha is the symbol which is used for the temperature coefficient of resistance is “α”.

Thus, if some copper wire of resistance 1OHM is heated through 1◦C and its resistance is then measured as 1.0043OHM then α=0.0043Ω/Ω◦C for copper. The units are normally expressed only as ‘per ◦C’, i.e. α=0.0043/◦Cfor copper. If the 1Ω resistor of copper is heated through 100◦C then the resistance was at 100◦C would be 1+100x0.0043=1.43Ω_.

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chemical effects of electricity

If we want  to conduct electric current it must contain charged particles to be able to conduct electric current. In solids, the current is carried by means of electrons. Copper, lead, aluminum, iron and carbon are few common examples of solid state conductors. In liquids and gases, the part of a molecule which has acquired an electric charge is a mean of conduction electric current, called ions. These ions may possess either a positive or negative charge, and their examples include the hydrogen ion H+, copper ion Cu++ and hydroxyl ion OH−. Distilled water possesses no ions and is considered as a poor form of conductor of electricity, on the other hand salt-water contains ions and is considerably a good conductor of electricity.

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Mesh-current analysis

The Mesh-current analysis is simply an extended application of Kirchhoff’s laws. Diagram 31.1 shows a network whose circulating currents I1, I2 and I3 have been allocated to closed loops in the circuit rather than to branches. Currents I1, I2 and I3 are referred to as mesh-currents or loop-currents. In mesh-current analysis the loop-currents are all arranged to circulate in the same direction (in diagram 31.1, shown as clockwise direction). Kirchhoff’s 2nd law is applied to each of the loops in turn, which in the circuit of diagram 31.1 generates 3 equations in three unknowns which may be solved for I1, I2 and I3.

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Maximum power transfer theorems

The maximum-power transfer theorem has effective applications in stereo amplifier design, where it is essential to maximize power delivered to speakers, and it is useful in electric vehicle construction, where it is required to maximize power supplied for driving a motor.

A network that consists of linear impedances & 1 or more voltage or current sources can be reduced to a Théven in equivalent circuit.When a load is connected to the terminals of this equivalent circuit, power is transferred from the source to the load.

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Main effects of electric current

There are three main effects of an electric current:

(a) magnetic effect

(b) chemical effect

(c) heating effect

Listed below are few practical applications and uses of these effects of an electric current:

• Magnetic effect:

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Magneto motive force and magnetic field strength

The Magneto-motive force (mmf) is the cause due to the presence of the a magnetic flux in a magnetic circuit,

mmf,Fm=NI amperes

where N is used to represent the number of conductors (or turns) and I represents the current in amperes. We sometimes express the unit of mmf as ‘ampere-turns’. As we know, since ‘turns’ have no dimensions, the SI unit of mmf is the ampere. Magnetic field strength (or magnetizing force),

H= NI/l ampere per metre

where l stands for the mean length of the flux path in metres.

Thus mmf =NI= Hl amperes.

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Transistor classification

This tutorial is about the kinds of transistors in which they are available. There are 2 main classifications of transistors. These two main classes are bipolar and field effect. Transistors are also classified on the basis of the semiconductor material used silicon or germanium, and also on the basis of their field of application (for example,general purpose, switching, high frequency, and much more). Transistors are also classified on the grounds of their application for which they are designed for. Table below shows the various categories of tansistors.

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Introduction to batteries

A battery is a useful device widely used to convert chemical energy into electricity. If we place an electric appliance in between its terminals the current produced will power the device. Battery is an indispensable item for many electronic devices and it is essential for devices that require power when no mains power is available. For example, without the battery, there would be no question of mobile phones or laptop computers.

The battery was invented 200 years back and these batteries are found almost everywhere in consumer and industrial products. Some common and practical examples where batteries are used include:

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