Electro Delight

Construction and application of cells

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Cell
If two dissimilar metals are immersed in an acid or salt solution, known as an electrolyte, an e.m.f. will be produced; this assembly is known as a cell.

The e.m.f. may be used to supply a load, but will only do so for a limited time, as the chemical qualities of the electrolyte deteriorate with use. The chemicals have to be renewed to render the cell useful again.

A. The primary cell

The most common forms of primary cells in use are the Leclanch´e wet cell and the dry cell.

The depolarizing agent is used to remove hydrogen bubbles from around the carbon rod. These bubbles, which are formed during the chemical action, impair the performance of the cell.

Applications
The dry cell has an obvious advantage over the wet cell because it is portable and so is commonly used for appliances such as torches, door bells, etc.
The wet cell, although almost obsolete, is used in larger bell and indicator circuits and for railway signalling.

B. The secondary cell
Unlike the primary cell, the secondary cell can be used again after it has discharged all its electrical energy. It can be recharged by supplying it with electrical energy. This reverses the chemical process which took place during discharge.
There are two types of secondary cell, the lead–acid and the alkaline cell.

The lead–acid cell
This cell consists of positive and negative lead electrodes, and an electrolyte of dilute sulphuric acid all placed in an acid-resistant container.
The electrodes are made of several plates, the positive and negative being insulated from one another by separators of insulating material such as wood or ebonite.
The construction of the plates is of considerable importance and is discussed below.

Formed plates
Repeated charging and discharging of a cell under manufacture causes the plates to be covered in lead compounds, the negative plate with spongy lead and the positive plate with lead peroxide, these being important to the chemical action of the cell. This process is, however, both expensive and time consuming and for smaller types of cell, pasted plates are more popular.

Pasted plates
These plates are manufactured in the form of a grid, into which a compound of sulphuric acid and red lead is pressed; only a short initial charge is needed for the cell to be ready for use. These plates, however, disintegrate more easily than the formed type.
A combination of formed and pasted plates is used in large-capacity cells; the positive plate is formed and the negative plate is pasted.
When current is drawn from the cell the active chemicals on the positive plate expand and the plate tends to distort, especially under heavy loads. Some measure of protection against this distortion or buckling, is achieved by arranging for each positive plate to be adjacent to two negative plates.

Action of lead–acid cell
When an external load is connected to the terminals of the cell, electrical energy
is delivered to the load. During this discharge period, a chemical reaction between the plates and the electrolyte takes place and a layer of lead sulphate is deposited on the plates. However, this process successively weakens the electrolyte until the cell is unable to deliver any more electrical energy.

If a D.C supply is then connected to the cell terminals, and a current is passed through it, the lead sulphate is converted back into sulphuric acid and restores the cell to its original condition. This process is known as charging.

Electrostatic

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Definition of electrostatic
electrostatics is that branch of science which deals with the phenomena associated with electricity at rest.

Generally an atom is electrically neutral i.e. in a normal atom the aggregate of positive charge of protons is exactly equal to the aggregate of negative charge of the electrons.
If, somehow, some electrons are removed from the atoms of a body, then it is left with a preponderance of positive charge. It is then said to be positively-charged. If, on the other hand, some electrons are added to it, negative charge out-balances the positive charge and the body is said to be negatively charged.
In brief, we can say that positive electrification of a body results from a deficiency of the electrons whereas negative electrification results from an excess of electrons.
The total deficiency or excess of electrons in a body is known as its charge.

Laws of Electrostatics
1. First Law. Like charges of electricity repel each other, whereas unlike charges attract each other.
2. Second Law. According to this law, the force exerted between two point charges (i) is directly proportional to the product of their strengths (ii) is inversely proportional to the square of the distance between them.
This law is known as Coulomb’s Law

TYPES OF CAPACITORS

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Capacitor
A capacitor essentially consists of two conducting surfaces separated
by a layer of an insulating medium called dielectric. The conducting surfaces may be in the form of either circular (or rectangular) plates or be of spherical or cylindrical shape.

A capacitor has the ability to store a quantity of static electricity.

The insulating medium separating charged surfaces is called a dielectric.

Capacitance: symbol, C ; unit, farad (F)
The unit of capacitance is the farad and may be defined as: ‘the capacitance
of a capacitor which requires a potential difference of 1 volt to maintain a
charge of 1 coulomb on that capacitor.’
Hence,
charge = capacitance × voltage
Q(C) = C(F) × V(V)

Types of capacitors
types of capacitor are characterized by the material used for their dielectric.
The main types include: variable air,mica,paper,ceramic,plastic,titanium oxide and electrolytic.

Variable air capacitors. These usually consist of two sets of metal plates (such as aluminium) one fixed, the other variable. The set of moving plates rotate on a spindle.

A variable air capacitor

As the moving plates are rotated through half a revolution, the meshing, and therefore the capacitance, varies from a minimum to a maximum value.
Variable air capacitors are used in radio and electronic circuits where very low losses are required,or where a variable capacitor is needed. The maximum value of such capacitors is between 500pF and 1000pF

Mica capacitors. Usually the whole capacitor is impregnated with wax and placed in a Bakelite case. Mica is easily obtained in thin sheets and is a good insulator.

However, mica is expensive and is not used in capacitors above about 0.2 µF . A modified form of mica capacitor is the silvered mica type. The mica is coated on both sides with a thin layer of silver which forms the plates. Capacitance is stable and less likely to change with age. Such capacitors have a constant capacitance with change of temperature, a high working voltage rating and a long service life and are used in high frequency circuit with a fixed capacitance up to about 1000pF.

Paper capacitors.

the length of the roll corresponds to the capacitance required. The whole is usually impregnated with oil or wax to exclude moisture,and then placed in a plastic or aluminium container for protection. Paper capacitors are made in various working voltages up to about 150kV and are used where loss is not very important. The maximum value of this type of capacitor is between 500pF and 10 µF. Disadvantages of paper capacitors include variation in capacitance with temperature change and a shorter service life than most other types of capacitor.

Ceramic capacitors. These are made in various forms, each type of construction depending on the value of capacitance required.

For high values, a tube of ceramic material is used .For smaller values the cup construction is used and for still smaller values the disc construction plates and with a thick absorbent material, such is used. Certain ceramic materials have a very high permittivity and this enables capacitors of high capacitance to be made
which are of small physical size with a high working voltage rating. Ceramic capacitors are available in the range 1pF to 0.1 µF and may be used in high frequency electronic circuits subject to a wide range of temperatures

Plastic capacitors. Some plastic materials such as polystyrene and Teflon can be used as dielectrics.

Construction is similar to the paper capacitor but using a plastic film instead of paper. Plastic capacitors operate well under conditions of high temperature,provide a precise value of capacitance, a very long service life and high reliability.

Titanium oxide capacitors have a very high capacitance with a small physical size when used at a low temperature.

Electrolytic capacitors. Construction is similar to the paper capacitor with aluminium foil used plates and with a thick absorbent material, such as paper, impregnated with an electrolyte(ammonium borate), separating the plates. The finished capacitor is usually assembled in an aluminium container

Connection and hermetically sealed. Its operation depends on
the formation of a thin aluminium oxide layer on the positive plate by electrolytic action when a suitable direct potential is maintained between the plates. This oxide layer is very thin and forms
coating the dielectric. (The absorbent paper between the plates is a conductor and does not act as a dielectric.) Such capacitors must always be used on dc and must be connected with the correct polarity; if this is not done the capacitor will be destroyed since the oxide layer will be destroyed. Electrolytic capacitors are manufactured with working voltage from 6V to 600V, although accuracy is generally not very high. These capacitors possess a much larger capacitance than other types of capacitors of Conducting similar dimensions due to the oxide film being only coating a few microns thick. The fact that they can be used only on dc supplies limit their usefulness.

Electrolysis and applications

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Electrolysis is the decomposition of a liquid compound by the passage of electric current through it.

An electrolyte is a compound which will undergo gen electrode. The electrochemical series is a way electrolysis. Examples include salt water, copper sulphate and sulphuric acid.

The electrodes are the two conductors carrying current to the electrolyte. The positive-connected electrode is called the anode and the negative-connected electrode the cathode

APPLICATION

Electroplating uses the principle of electrolysis to apply a thin coat of one metal to another metal. Some practical applications include the tin-plating of steel,silver-plating of nickel alloys and chromium-plating of steel. If two copper electrodes connected to a battery are placed in a beaker containing copper sulphate as the electrolyte it is found that the cathode (i.e. the electrode connected to the negative terminal of the battery) gains copper whilst the anode loses copper.

1.10.2.2 Definition of electricity

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The name electricity implies the importance of the almost weightless, invisible

part of an atom called an electron. It is electrons that cause electricity. Electricity is defined as the movement of electrons along a conductor.

An electron is only one part of an atom. An atom is only one part of a molecule. None of these can be seen by the unaided eye. Thus, most actions in electric circuits cannot be seen. An electric circuit can appear motionless although great activity is happening within it at the atomic level.
The electron can be controlled. Control of the electron is the task of an electrician, electrical engineer, or anyone else working with electricity.

Solar electricity handbook

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Title : Solar Electricity handbook
Author : Michael Boswell
Size : 4.18 MB
Pages : 212
Year : 2017

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1.8.1.4 Classification of fire

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Fire

Safety with fire
Fire fighting is highly skilled operation, and most medium and large firms have properly trained teams who can contain the fire before the arrival of the special trained fire brigades.

In an industry or workshop fire can be caused by a number of mechanisms. Most of these causes of fire are brought about by mishandling special equipment and misuse/careless use of electrical implements.
The personnel working in the firm may also cause fire if they don't follow the specified rules and regulations

Classes of fire
Fire can be classified into four major categories
These categories are determined by the kind of material being burnt.

1. Class A fires
These are fires that occur on ordinary combustible materials e.g paper,fabrics, wood
These types of fire is the commonly known type in day to day life.
For these fire to be put off, these can be done by removal or reduction of heat (lowering the temperature)
These types of fire is easily put off by water extinguisher, carbon dioxide extinguisher can also be used to put off class A fire.

Water extinguished	carbon dioxide extinguisher

2. Class B fires

These fires can easily occur on flammable/combustible liquids example petrol, kerosene oils and other lubricants
These fires are dangerous in industry and can cause large explosions.
For these types of fires to be put off one has to remove oxygen from the region of fire.
These fires can be well extinguished by use of carbon dioxide extinguisher
Class B fires can also be extinguished by use of foam or powder extinguisher.

Carbon dioxide extinguisher	foam extinguisher	powder extinguisher

Advance engineering mathematics

2020-05-06T07:55:00.000-07:00

Tittle : Advance engineering mathematics
Author : DEXTER J. BOOTH
Size : 52.14 MB
Pages : 1,056
Year : 2003

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1.6.1.1 STRUCTURE of ATOM

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Atomic structure

Structure and properties of nucleus

A nucleus is made up of protons and neutrons

A proton is positively charged : its mass is
Mp = 1.67262 x10^-27 kg

A neutron is electrically neutral : mass of
Mn = 1.67493 x10^-27 kg

Neutrons and protons are collectively called nucleon
The different nuclei are referred to as nuclides
Number of protons : atomic number Z
Number of nucleons : atomic mass number A
neutron number : N=A-Z Therefore A and Z are sufficient to specific nuclide

Nuclides are symbolized as

X is the chemical symbol of the element, it contains the same information as Z but in a more easily recognized form
Nuclei with the same Z so they are the same elements but different N are called isotopes
For many elements , several different isotope exist in nature
Nature abundance is the percentage of a particular element that consists of a particular isotope in nature

Reference
Physical science

1.7.1.1 Forms of energy

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Work - is the force causing movement or displacement of an object from one place to another in the direction of force.

Energy - is the capacity for doing work
Power - is the rate of doing work

Forms of energy
Energy existing different forms such as heat, light, chemical,...etc but the most important is electrical energy.

Importance of electrical energy
Energy may be needed as heat, light, as motive power,...etc electrical energy is superior to all other forms of energy due to the following reasons.

Convenient form it can be easily converted into other forms of energy. Example light by use of a bulb, heat by use of a high resistance wire, mechanical energy by the use of a motor
Easy control electrically operated machines have simple and convenient starting, control and operation
Great flexibility one important reason for preferring electrical energy is the flexibility that it offers. It can be easily transported from one place to another with the help of conductor.
Cheapness it is cheaper than other forms of energy. Thus its overall economical to use this form of energy for domestic, commercial and industrial purpose.
Cleanliness it is not associated with smoke, fumes or poisonous gases . therefore, its use ensure cleanliness and healthy conditions
High transmission efficiency electrical energy can be transmitted conveniently and efficiently from centre of generation to the consumer with help of overhead conducts known as transmission lines.

1.10.1.3 Unites of electrical quantities

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The following units are used in electrical measurement

Quantity	Quantity symbol	Unit	Unit symbol
Lenght	L	meter	M
Mass	M	kilogram	Kg
Time	t	seconds	s
Velocity	v	meters per second	M/s
Acceleration	a	meter per second squared	M/s²
Force	F	Newton	N
Electrical quantity/charge	Q	Coulomb	C
Electric current	I	ampere	A
Resistance	R	ohms	Ω
Ωഉ൨ΩΩΩΩΩConductance	G	Siemen	S
Electromotive force	V	volt	V
Potential difference	V	volt	V
Work	W	joule	j
Energy	E	joule	j
Power	P	watt	W

Reference

Electrical Circuit Theory and Technology by John Bird (chapter 1)

1.10.1.2 DERIVED UNITS

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Derived SI units

They are units of measurement derived from the seven base units

Velocity = meters per second (M/s)

Acceleration = meters per second squared (M/s²)

Reference

Electrical Circuit Theory and Technology by John Bird (chapter 1)

1.10.1.1 Basic SI Unit

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Basic SI units

The system of units used in engineering and science is known as Systéme Internationale unites AKA international syestem of units

Quantities		units
Length	M	Meters
Mass	Kg	kilograms
Time	S	seconds
Electric current	A	Amperes
Thermodynamic temperature	K	Kelvin
Luminous intensity	cd	cadela
Amount of substance	Mol	mole

1.10.4.3 series circuit

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series circuit
Is when resistors are connected end to end in a circuit

The current is the same through all resistors
The voltage measured from individual resistor is equal to supplied voltage

The total resistance is obtained by adding together the value of separate resistor

Reference

Electrical Circuit Theory and Technology by John Bird (chapter )

1.10.4.4 parallel series

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Parallel series

This is when resistors are connect across each other in a circuit

The sum of separate current is equal to the total current in a circuit
Voltage remains the same across each resistor

Reference

Electrical Circuit Theory and Technology by John Bird (chapter )

1.5.1.2 Logarithm

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Logarithms

Logarithms are another way of writing indices.

If a = b^c then c = log_ba

Example

We know that 10² = 100
Therefore, log₁₀100 = 2

You may often see ln x and log x written, with no base indicated. It is generally recognised that this is shorthand:

log_ex = lnx

log₁₀x = lgx or logx (on calculators)

Remember that e is the exponential function, equal to 2.71828…

Laws of Logs

The properties of indices can be used to show that the following rules for logarithms hold:

log_ax + log_ay = log_a(xy)

log_ax – log_ay = log_a(x/y)

log_axⁿ = nlog_ax

Example

Simplify: log 2 + 2log 3 - log 6
= log 2 + log 3² - log 6
= log 2 + log 9 - log 6
= log (2 × 9) - log 6
= log 18 - log 6
= log (18/6)
= log 3

NB: In the above example, I have not written what base each of the logarithms is to. This is because for the laws of logarithms, it doesn"t matter what the base is, as long as all of the logs are to the same base.

Another important law of logs is as follows. This is a very useful way of changing the base (in this formula, the base does matter!). Most calculators can only work out ln x and log₁₀x (usually just written as "log" on the button) so this formula can be very useful.

Example

Calculate, to 3s.f., log₃5

log₃5 = log₁₀5 = 1.46 (3s.f.)
log₁₀3

1.5.1.1 Indices

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An index number is a number which is raised to a power. The power, also known as the index, tells you how many times you have to multiply the number by itself. For example, 2⁵ means that you have to multiply 2 by itself five times = 2×2×2×2×2 = 32.

There are a number of important rules of index numbers:

y^a × y^b = y^a+b

Examples

2⁴ × 2⁸ = 2¹²

5⁴ × 5^-2 = 5²

y^a ÷ y^b= y^a-b

Examples

3⁹ ÷ 3⁴ = 3⁵

7² ÷ 7⁵ = 7^-3

y ^-b = 1/y^b

Examples

2^-3 = 1/2³ = 1/8

3^-1 = 1/3

y^m^/n = (ⁿ√y)^m

Examples

16^1/2 = √16 = 4

8^2/3 = (³√8)² = 4

(yⁿ)^m = y^nm

Example

2⁵ + 8⁴

= 2⁵ + (2³)⁴

= 2⁵ + 2¹²

y⁰ = 1

Example

5⁰ = 1

Electrical technology volume 4

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Tittle : A textbook of electrical technology By A textbook of electrical technology By thereja-volume 4-volume 4
Author : thereja
Size : 19.0 MB
Pages : 733
Year :

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