Radio wave propagation

Introduction :
A radio wave is an electromagnetic wave whose frequency is lower than 3000 GHz, a wavelength greater than 0.1 mm.

The field of radio is regulated by the International Telecommunication Union (ITU) has established rules of radio communications in which one can read the following definition:

Radio waves or radio waves "electromagnetic waves with frequencies arbitrarily lower than 3000 GHz propagated in space without artificial guide" can be between 9 kHz and 3000 GHz which corresponds to wavelengths 33 km to 0.1 mm.

The wave frequency below 9 kHz radio waves are, however are not regulated.

The radio waves  are electromagnetic waves which propagate in two ways:
  * In the free space propagation (radiated around the Earth for example)
  * In lines (guided propagation in a coaxial cable or waveguide)

The field frequency radio waves ranges from 9 kHz to 3000 GHz.

Radio or electromagnetic wave in space :

The waves caused by a falling rock on the surface of a pond spread like concentric circles. The radio waves emitted by the isotropic antenna (that is to say, radiating uniformly in all directions in space) can be represented by a series of concentric spheres. One can imagine a balloon inflating fast, the speed of light c, very close to 300,000 km / s. After one second, the sphere has 600,000 km in diameter. If the propagation medium is not isotropic and homogeneous, the wave front will not be a sphere. As the radio wave is a vibration, after a period, the wave has traveled a distance denoted lambda and called wavelength. The wavelength is a key feature in the study of the spread, for a given frequency, it depends on the speed of wave propagation.

Radio Wave propagation in a line:

A generator connected to a load with a line will cause each of the two conductors of the line to establish an electric current and the formation of a wave moving in the dielectric at high speeds. This speed is less than the speed of light but frequently exceeds 200 000 km / s, which implies that for a given frequency, the wavelength in the line is smaller than in space.

In a coaxial line, the propagation speed is the same regardless of frequency, we say that the line is dispersive.

Propagation of electromagnetic waves

Propagation of Waves

 The process of communication involves the transmission of information from one location to another.  As we have seen, modulation is used to encode the information onto a carrier wave, and may involve analog or digital methods. It is only the characteristics of the carrier wave which determine how the signal will propagate over any significant distance.  This chapter describes the different ways that electromagnetic waves propagate.

Basics

An electromagnetic wave is created by a local disturbance in the electric and magnetic fields.  From its origin, the wave will propagate outwards in all directions.

If the medium in which it is propagating (air for example) is the same everywhere, the wave will spread out uniformly in all directions.

Far from its origin, it will have spread out enough that it will appear have the same amplitude everywhere on the plane perpendicular to its direction of travel (in the near vicinity of the observer). This type of wave is called a plane wave. A plane wave is an idealization that allows one to think of the entire wave traveling in a single direction, instead of spreading out in all directions.

Electromagnetic Wave Propagation at the speed of light in a vacuum. In other mediums, like air or glass, the speed of propagation is slower. If the speed of light in a vacuum is given the symbol c0, and the speed in some a medium is c, we can define the index of refraction, n as: 
Refraction

When the wave enters the new medium, the speed of propagation will change. In order to match the incident and transmitted wave at the boundary, the transmitted wave will change its direction of propagation.  For example, if the new medium has a higher index of refraction, which means the speed of propagation is lower, the wavelength will become shorter (frequency must stay the same because of the boundary conditions).  For the transmitted wave to match the incident wave at the boundary, the direction of propagation of the transmitted wave must be closer to perpendicular.

The relationship between the angles and indices of refraction is given by Snell's Law:
ni sinI = nt sint

Alkane nomenclature practice

Introduction :
Alkanes are the saturated hydrocarbons consisting elements of carbon (C) and hydrogen (H) in which atoms are linked together by single bonds. Alkanes are the member of a homologous series of organic compounds, where all members differ by a constant relative molecular mass of 14.

Each carbon atom have 4 single bonds (either C-H or C-C bonds), and each hydrogen atoms are joined to a carbon atom. A series of linked carbon atoms is known as the carbon skeleton or carbon backbone...The first member of alkane is methane, CH₄.

Structure and Isomerism of Alkanes:

Saturated hydrocarbons, Alkanes, may occur in linear, branched or cyclic forms. Alkanes having linear structure must have n<3.In this all the carbon  are attached  in a snake-like structure and alkanes having branched structure must have n>3. Alkanes having cyclic structure must have n>2.Alkanes having more than three carbon atoms are arranged in number of ways, so they form different structural isomers.

• First three members i.e. methane, ethane, and propane have one isomer.  
• Butane ,C₄H₁₀ has 2 isomers. they are n-butane, isobutene
• Pentane ,C₅H₁₂  has 3 isomers. They are pentane, isopentane, neopentane 
• Hexane, C₆H₁₄ has five  isomers
• Branched alkanes are chiral, e.g., 3-methylhexane and its higher homologues

Alkane nomenclature practice

• The number of carbon atoms can be indicated by ‘meth’ for one carbon atom, ‘eth’ for two , ‘prop’ for three, ‘but’ for four , ‘pent’ for five and so on…..

• Alkanes or saturated carbon atoms can be named by adding ‘ane’ suffix to the number of carbon atoms’ name. e.g., CH₄ can be named as methane. C₂H₆ can be named as ethane .First three members of alkanes form linear structure, so they have one isomer each.  

    Butane has two isomers. It can be named by using following rules:

• For naming branched chain isomers, firstly number of carbon atoms in series are counted and named according to it.

• Then number of methyl group is counted and also its position is located.

As per the IUPAC convention, we have certain rules to follow:

• First we have to find and then name the longest chain of carbon.
• Next we have to identify the groups which is being attached to the chain, after that we name it.
• Number the C- atoms in a chain that starts from the nearest substituent group.
• Assign the position of each group by a proper number and then we name it.
• Write the name of the listing groups which should be in an alphabetical order.
• di, tri, tetra, are used as prefix to assign several groups of similar kind. Alphabetizing is not taken into account.

E.g.  
1. C₄H₁₀           `->`     common name – n-butane      IUPAC name- butane 

 

2.

 

IUPAC names of the above alkane is 2- methylpropane

3.

IUPAC name of the above alkane is 2-methylbutane

4.

IUPAC name of the above alkane is 2,2-dimethylpropane

Conclusion for the nomenclature of alkane

From the discussion, we conclude that, in alkane each carbon atom have 4 single bonds and each hydrogen atom must be joined to a carbon atom .There is single bond between each carbon atom. They are saturated hydrocarbons.

Nomenclature of coordination compounds

Define nomenclature:
Nomenclature is significant in the coordination of chemistry because of the need to have an unambiguous method of describing formula and writing systematic names, particularly when dealing with isomer. The formulas and names adopted for ordination entities are based on the recommendation of the international union of pure and applied chemistry. A complex is an essence in which a metal atom or ion is linked with a collection of neutral molecules or anions call ligands.

Formulas of mononuclear coordination entities:

The formula of a compounds is shorthand tools used to provide basic information about the constitution of the compounds in the concise and convenient manner. Mononuclear synchronization entities include a particular central metal atom. Nomenclature coordination compounds are neutral substances in which at smallest amount one ion is absent as a complex.

• The central atoms is listed first
• The ligands are then listed in alphabetic order.
• Polydentate ligands are also scheduled alphabetically.
• The method for the complete coordination unit, whether charged or not is together with this in square brackets.
• There should be no space between the ligands and metal within the coordination.

Naming of mononuclear coordination compounds:

• The names of nomenclature coordination compounds are derivative by subsequent the principle of additive nomenclature. Thus the groups that surround the central atoms must be identified in the name.
• The cation is named primary in together positively and negatively charged coordination entity.
• The ligands are name in an alphabetical organize prior to the name of the central atom/ion.
• Names of the anionic ligands end in –o those of neutral and cationic ligands are the same except aqua for H₂O, ammine for NH₃, carbonyl for CO and Nitrosyl for NO. These are placed within enclosed marker ().
• When the name of the ligands include a numerical prefix, then the terms, bis, tris, tetrakis are used, the ligands to which they refer being placed in dichlorobis.
• Oxidation state of the metal in cation, anion or neutral coordination entities is indicating by Roman numeral in parenthesis
• If the complex ion is a cation, the metal is named same as the element. The neutral complex is named similar to that of the complex cation.

Making molar solutions

Introduction :
The amount of substance present in unit amount of the solution is called concentration of the solution.  Generally, concentration of a solution is expressed in
(a) molarity, M     (b) molality, m  or    (c) normality, N
Molarity:
“The number of gram molecular weight of the solute present in 1000 cm³ (or 1 dm³) of the solution is called molarity”.  It is denoted by the symbol M.

Making molar solutions Case1 and 2

Case 1:
Suppose 1 mole of Oxalic acid crystals (H₂C₂O₄. 2H₂O, Molecular weight 126g) is dissolved in 1dm³ of the solution. Molarity of the solution is 1.
Molarity of the solutions can be calculated from the expression
Formula for Molarity = (mass/dm³) / molecular weight
Case 2:
Suppose ‘x’ molar solution of Oxalic acid is asked to prepare.  Then, the weight of the Oxalic acid corresponding to ‘x’ mole of Oxalic acid is used in making x molar solution.
That is weight of Oxalic acid required is = ‘x’ moles X molecular weight of Oxalic acid
                                                                        = molarity X 126g
This much of Oxalic acid should be dissolved in 1 dm³ of solvent.

Making molar solutions Case3 ,4 and relation between molarity & normality

Case 3:
For the making of  ‘x’ molar solutions of Oxalic acid of a volume, say 100ml, the weight of the oxalic acid required is found using the below relation.

Case 4:

If a liquid reagent of certain % assay and density is given in the making of certain molar solutions, then the strength of the given liquid reagent should be determined first.  This is done by using the relation.

Strength = number of moles / dm³
               = (weight in g / Molecular weight) / dm³
               = density / Molecular weight
Now, the strength of the liquid reagent given is used in the making of the solution of required strength and volume using the below relation.
M₁.V₁ = M₂ V₂
Where:
M₁, M₂ are the molarities of the given liquid reagent and solution to be prepared
V_1, V₂ are the volumes of the given liquid reagent and solution to be prepared, respectively.
Since, Equivalent weight and Molecular weight are related as:

So, there exists a relation between the molarity and normality as below:
Molarity = (mass/dm³) / Mol. Wt
               = (mass/dm³) / [Eq. wt x valence (number of electron exchange)]
Molarity = Normality / valence    or
Normality = Molarity X valence         is used in the making of N solutions from M solutions.

Mass and volume relationship

Introduction 
Mass is the measure of inertia.  Mass of an atom is composed of the mass of the protons and the mass of the neutrons.  The mass of the electrons is negligible. It is the same thing with molecules.   The mass of a particular compound is the mass of its molecules.

 Similarly, volume is also a property exhibited by any gas. It is the space occupied by a gas.  Each gas at a certain temperature has a specific volume depending upon its mass. There is a certain co-relationship between mass and the volume of the gas at a particular temperature.

Mass and molar mass definition :

In chemistry, the mass is often expressed in terms of molar mass. The molar mass is the mass of one mole of a gas.  One mole of a gas is nothing but gram equivalent of the gas.
 To illustrate, take the gas, carbon monoxide, the molar mass of carbon monoxide is 12+ 16 = 28. 

When this mass which is in atomic mass unit is expressed in grams instead of atomic mass unit it is called as one mole. 

So one mole of carbon dioxide is 28 grams. And it has been proved that there is definite relationship between the volume and molar mass of the gas.

The relationship between the molar mass and the volume is that 1 mole of the gas would occupy 22.4 liters of volume. 

In the above case where the molar mass of carbon dioxide is 28, 28 grams of carbon dioxide would occupy 22.4 liters of volume.  This relationship was developed from the equation of ideal gas i.e. PV = nRT, where 'n' is number of moles. 

At standard temperature and pressure the values of which are 273° kelvin and 1 atmosphere, the volume figure derived is 22.4 liters. 

If the mass of a gas is expressed as 'z' then it can be said that 'z' grams of a gas occupy (z/molar mass x 22.4) liters of volume.

Illustration of mass and volume relationship

Find the volume occupied by 56 grams of carbon dioxide.
The molar mass of carbon dioxide is 28;
hence number of moles = 56 / 28 = 2 moles.
 Since one mole occupies 22.4 liters at STP,
2 moles of carbon dioxide would occupy 44.8 liters of volume.

Amplitude Modulation Side Band

Introduction :-

Modulation is the process of changing one or more properties like amplitude, frequency, phase of high frequency carrier wave in accordance with the Modulating wave. Here the Modulating wave is base-band signal. Example of base-band signal is speech or music signal.

what is amplitude modulation : Amplitude Modulation is the process of changing Amplitude of high frequency carrier wave in accordance with the Amplitude of Modulating wave.

Definition of Side-Band:

A group of frequencies which is having frequency fc±fm is called as Side-Band. Here fc=Carrier frequency and fm=modulating frequency. fc+fm is called as upper side-band and fc-fm is called as lower side-band.

Different types of Amplitude Modulation

Depending on side-bands we have 5 different types of Amplitude Modulation.

1. Double-Sideband Full Carrier

2. Single-Sideband Full Carrier

3. Single-Sideband Reduced Carrier

4. Vestigial-Sideband

1. Double-Sideband Full Carrier:

The technique of amplitude modulation in which along with the carrier if both upper side-band and lower side-band is transmitted then that amplitude modulation is called as Double-Sideband full carrier.

In order to increase the efficiency of transmitter we may suppress the carrier from this DSB-AM then that technique is called as Double-Sideband Suppressed carrier Amplitude Modulation Method.

This type of amplitude Modulation is also called as conventional amplitude modulation

2. Single-Sideband Full carrier:

The technique of amplitude modulation in which single side-band is transmitted is called as single-sideband Full carrier and is denoted as SSB.

This type of modulation technique is used in shortwave radio or shortwave broadcasting

3. Single-Sideband Reduced Carrier:

The technique of amplitude modulation in which carrier and single side band is suppressed then that type of amplitude modulation is called as single-sideband Reduced carrier.

This type of modulation technique is used in amateur radio.

4. Vestigial-Sideband:

The technique of amplitude modulation in which part of single side band and all other remain as it is ,then that type of amplitude modulation in called as vestigial side-band.

This type of modulating technique is used in transmission of Television i.e., Television broadcasting.