Category: Physics Notes PPT

A rigid body is usually defined as a hard solid object with a definite shape and size. However, in reality, bodies can be compressed, stretched, and bent. Also, the appreciably rigid steel bar can be deformed with the application of a sufficiently large external force on it. It implies that solid bodies are not perfectly rigid. A solid body has a definite shape and size. For changing or deforming the shape or size of a body, an external force is needed. By stretching a helical spring or gently pulling its ends, the length increases slightly. Furthermore, when you leave the ends of the spring, it comes back to its original shape and size. The property of a body by which it tends to regain its original size and shape when the applied force is removed is what we refer to as elasticity, and the deformation caused is called elastic deformation. However, if we apply an external force to a lump of putty or mud, they won’t regain their previous shape as they do not tend to do so, and get permanently deformed. Such kinds of substances are called plastic, and the property is known as plasticity.

The elastic behaviour of materials or the property of elasticity plays a significant role in engineering design. For instance, while designing a building, having some knowledge of the elastic properties of materials like concrete, steel, etc is essential. The same holds for the design of bridges, automobiles, rope ways, etc.

Stress-strain Curve

The relationship between stress and strain for a given material under tensile stress can be proved with the help of an experiment. In a standard test of tensile properties, a test cylinder or wire is stretched by an external force. The fractional change in length or strain and the applied external force needed to cause the strain are recorded. The applied external force is gradually increased in steps, and the change in length is also recorded. A graph is plotted between the stress (which is equal in magnitude to the applied external force per unit surface area) and the strain produced. A typical graph for metal is shown below.

The stress-strain curves vary from one material to the other. The stress-strain curves help us in understanding how a given material deforms with an increase in the load. From the graph, we can see and find that in the region between points O and A, the curve is linear. In this region, Hooke’s law is followed and obeyed. The body regains its original dimensions when the applied external force is removed. In this region, the solid body behaves as an elastic body. Moving ahead, in the region between points A and B, stress and strain are not directly proportional. Nevertheless, the body still tends to return to its original dimension when the load is removed. The point B in the curve is called yield point (also referred to as the elastic limit), and the corresponding stress is called yield strength (σy) of the material. If the load increases further, the stress shall also exceed the yield strength, and the strain increases rapidly, even for very little change in the stress. The portion of the curve between points B and D shows the same.

When the load is removed, say at some point C, between B and D, the body does not regain its original shape and size. In such a case, even when the stress is 0, the strain is not 0. The material is said to then have a permanent set. The deformation is known as plastic deformation. The point D on the graph refers to the ultimate tensile strength of the material. Beyond point D, additional strain is produced even by a reduced applied external force, and fracture occurs at point E. If the ultimate strength and fracture between points D and E are close, the material is referred to as brittle. If they are quite far apart, the material is referred to as ductile. The stress-strain behaviour varies from one material to another. For instance, rubber can be pulled several times, and it shall still return to its original shape. Although the elastic region is large enough, the material does not follow Hooke’s law in most of the regions. Secondly, there is no well-defined plastic region. The substances like rubber, which can be stretched to cause large strains, are known as elastomers.

Elastic Moduli 

The proportional region, within the elastic limit of the stress-strain curve (region OA in the above figure), is of utmost importance for both structural and manufacturing engineering designs. The ratio of stress and strain, known as modulus of elasticity, is found to be a significant characteristic or property of the material.

Bulk Modulus 

We already know and have seen as well that when a body is submerged in a fluid, it undergoes or experiences hydraulic stress, which is equal in magnitude to the hydraulic pressure. The same leads to a decrease in the volume of the body and produces a strain known as volume strain.

Bulk Modulus is defined as the ratio of hydraulic stress to the corresponding hydraulic strain. It is denoted by symbol B, and can be expressed as: 

B = [frac{-p}{(frac{∆V}{V})}]

The negative sign in the formula indicates that as the pressure increases, the volume decreases. To be specific, if p or pressure is positive, then ∆V or the change in volume is negative. Hence, for a system in equilibrium, the value of bulk modulus or B is always positive. The SI unit of the bulk modulus is the same as that of pressure that is N m2 or Pa. The bulk moduli of a few common materials are specified in the table below:

The reciprocal of the bulk modulus or ‘B’ is known as compressibility and is denoted by the symbol k. It is defined or expressed as the fractional change in volume per unit increase in pressure. 

k = ([frac{1}{B}]) = – ([frac{1}{∆p}]) × ([frac{∆V}{V}])

It can be seen from the data given in the table that the bulk moduli for solid bodies are much larger than it is for liquids, which are again much larger than the bulk modulus for gases like air.

Therefore, the solid bodies are the least compressible, whereas gases are the most compressible. Also, gases are somewhere around a million times more compressible than solids. 

Gases have large compressibility, which vary with both pressure and temperature. The incompressibility of the solids is primarily due to the tight coupling between the ne
ighbouring atoms. The molecules in liquids are also bound with their neighbours, but not as strong as in the case of solids. Molecules in gases are very poorly coupled to their neighbouring atoms.

In Physics there are two cavitations inertial cavitation and non-inertial cavitation. 

According to Cavitation meaning caused due to inertia “The phenomenon of a void or bubble in a liquid rapidly collapsing and creating a shock wave is known as the inertial cavitation”.

Inertial cavitation occurs as the bubble diameter expands to at least twice its original diameter over a single acoustic pressure period. The bubble then violently explodes due to the fluid’s inertia, potentially fragmenting into several smaller bubbles.

Local deposition of energy, such as an intense centred laser pulse or an electrical discharge through a spark, is another way to generate inertial cavitation voids. 

Vapour gases from the surrounding medium evaporate into the cavity, resulting in a low-pressure vapour bubble rather than a vacuum. 

If the conditions that caused the bubble to form no longer exist, such as when the bubble travels downstream, the surrounding liquid starts to implode due to its higher pressure, accumulating inertia as it moves inward.

As the bubble eventually bursts, the surrounding liquid’s inertia causes the vapour’s pressure and temperature to rise dramatically.

The bubble gradually collapses to a fraction of its original size, at which point the gas inside dissipates into the surrounding liquid, releasing a large amount of energy in the form of an acoustic shock wave and visible light. 

The temperature of the vapour inside the bubble can be several thousand kelvins, and the pressure several hundred atmospheres at the point of complete collapse.

In the presence of an acoustic field, inertial cavitation may also occur. Due to an applied acoustic field, microscopic gas bubbles that are commonly found in liquids would be forced to oscillate.

If the acoustic strength is high enough, the bubbles can increase in size before quickly collapsing. As a result, even if the rarefaction in the liquid is inadequate for a Rayleigh-like void to form, inertial cavitation will occur.

For the treatment of surfaces, liquids, and slurries, high-power ultrasonics typically depends on the inertial cavitation of microscopic vacuum bubbles.

The physical mechanism that causes cavitation to form is close to that of boiling. The thermodynamic paths that precede the creation of the vapour are the most significant difference between the two.

Boiling occurs when the liquid’s local temperature approaches saturation and additional heat is applied to allow the liquid to phase change enough into a gas. 

Cavitation begins when the local pressure falls far enough below the saturated vapour pressure, which is determined by the liquid’s tensile strength at a given temperature.

Non-inertial cavitation occurs when small bubbles in a liquid are induced to oscillate in the presence of an acoustic field when the amplitude of the acoustic field is inadequate to induce complete bubble collapse. This form of cavitation causes much less erosion than inertial cavitation, and it’s often used to clean fragile materials like silicon wafers.

The cavitation in fluid mechanics is known as hydrodynamic cavitation.

The process of vaporisation, bubble formation, and bubble implosion that occurs in a flowing liquid as a result of a decrease and subsequent increase in local pressure is known as hydrodynamic cavitation. 

Hydrodynamic cavitation occurs only when the local pressure falls below the saturated vapour pressure of the liquid and then rises above it. 

Flashing is said to have happened when the recovery pressure does not exceed the vapour pressure. 

Hydrodynamic cavitation usually occurs in pipe systems as a result of an increase in kinetic energy or an increase in pipe elevation.

Passing a liquid through a constricted channel at a given flow velocity or mechanical rotation of an object through a liquid may also cause hydrodynamic cavitation. 

The combination of pressure and kinetic energy will create the hydrodynamic cavitation cavern downstream of the local constriction, creating high energy cavitation bubbles, in the case of the constricted channel and based on the particular or special geometry of the system.

As a hydrodynamic cavitation flow progresses, various flow patterns are detected: inception, developed flow, supercavitation, and choked flow.

The first time the gas phase occurs in the system is called inception. This is the system’s weakest cavitating flow, which corresponds to the highest cavitation amount.

Established flow is recorded as the cavities in the orifice or venturi structures expand and become larger in size.

Supercavitation is the most extreme cavitating flow, in which all of an orifice’s nozzle region is potentially filled with gas bubbles. The lowest cavitation number in a system corresponds to this flow regime. 

The system is no longer capable of passing further flow after supercavitation. As a result, velocity does no
t change as upstream pressure rises. This will result in a higher cavitation number, indicating that a choked flow has occurred.

For a brief period of time, the process of bubble generation, followed by the growth and collapse of the cavitation bubbles, results in extremely high energy densities, as well as extremely high local temperatures and pressures at the surface of the bubbles. As a result, the total liquid medium environment remains at ambient levels. 

Cavitation is harmful when it is uncontrolled but by regulating the flow of the cavitation, the power can be harnessed and the damage avoided.

Since free radicals are formed as vapours trapped in cavitating bubbles dissociate, controlled cavitation can be used to enhance chemical reactions or propagate some unexpected reactions.

Cavitation is said to be widely produced using orifices and venturi meters. Because of its smooth converging and diverging parts, a venturi meter has an inherent advantage over an orifice in that it can produce a higher flow velocity at the throat for a given pressure drop through it. An orifice, on the other hand, has the advantage of being able to accommodate a greater number of holes in a given pipe cross-sectional area.

Some industrial processes will benefit from hydrodynamic cavitation. In dry milling facilities, for example, cavitated corn slurry produces higher yields in ethanol production than uncavitated corn slurry.

Since free radicals are produced in the process due to the dissociation of vapours trapped in the cavitating bubbles, this is often used in the mineralization of bio-refractory compounds that would otherwise require extremely high temperature and pressure conditions. This results in either the intensification of the chemical reaction or the propagation of certain reactions that would otherwise be impossible to propagate.

Cavitation is often used in manufacturing to homogenise, or blend and break down, suspended particles in a colloidal liquid compound like paint mixtures or milk.

Cavitating water purification devices have also been developed, allowing contaminants and organic molecules to be broken down by the extreme conditions of cavitation.

Underwater, cavitation attracts hydrophobic chemicals by forcing them to join together due to the pressure differential between the bubbles and the liquid water. It’s possible that this effect may help with protein folding.

In shock wave lithotripsy, cavitation plays a significant role in the destruction of kidney stones.

Cavitation is useful for non-thermal, non-invasive tissue fractionation in the treatment of a number of diseases, and it can also be used to open the blood-brain barrier and improve drug absorption in the brain.

High-intensity focused ultrasound (HIFU), a thermal non-invasive cancer treatment tool, uses cavitation as well.

Ultrasound is often used to promote bone formation.

The collapse of cavitation in the synovial fluid within the joint is thought to cause the sound of cracking knuckles.

Cavitation has enough strength in industrial cleaning applications to withstand particle-to-substrate adhesion forces, loosening pollutants.

Pasteurization of eggs has been done using cavitation. A rotor with holes creates cavitation bubbles, which heat the liquid from inside. Cavitation strength can be modified, allowing the process to be fine-tuned for minimal protein damage.

Cavitation is an unpleasant phenomenon in many situations. Cavitation causes a lot of noise, component damage, vibrations, and a loss of efficiency in devices like propellers and pumps.

Cavitation on the blade surface of tidal stream turbines has been a source of concern in the renewable energy industry.

When cavitation bubbles burst, they compress energetic liquid into very small sizes, resulting in hot spots and shock waves, all of which are disruptive. 

Cavitation noise is a particular issue for military submarines because it increases the likelihood of being detected by passive sonar.

Despite the fact that the collapse of a small cavity is a low-energy occurrence, highly localised collapses can erode metals like steel over time.

The pitting caused by the collapse of cavities causes a lot of wear on components and can drastically reduce the life of a propeller or pump.

When a surface is first affected by cavitation, it appears to erode at a faster rate. The cavitation pits increase fluid turbulence and create crevices that serve as nucleation sites for more cavitation bubbles. The pits also increase the surface area of the components and leave residual stresses behind. This increases the surface’s susceptibility to stress corrosion.

When water flows over a dam spillway, the defects on the surface create small areas of flow separation in a high-speed flow, lowering the pressure in these areas. If the flow velocities are high enough, the pressure can drop below the water’s local vapour pressure, resulting in the formation of vapour bubbles. When these bubbles are carried downstream into a high-pressure environment, they collapse, resulting in high pressures and the possibility of cavitation damage.

Due to high compression and undersized cylinder walls, cavitation occurs in some larger diesel engines. Vibrations of the cylinder wall cause the coolant against the cylinder wall to have alternating low and high pressures. Pitting of the cylinder wall occurs as a result of this, allowing cooling fluid to leak into the cylinder and combustion gases to leak into the coolant.

What is Charge Transfer?

The charge transfer is illustrated as an electron donor and electron acceptor facility, branded by electronic transitions to an excited state.

There is a fractional transfer of elementary charge from the giver to the recipient in this excited state. In the ultraviolet-visible region, nearly whole charge transfer complexes have strong absorption & exclusive bands.

Separated from charge transfer, connections between giver and recipient, the electrostatic forces also persist. The existing forces are generally much punier than covalent bonds or hydrogen bonds, however valuable for making crystal structures.

Charge Transfer and its Methods 

You might have known that when we charge a piece of plastic, a comb, or a pen and place it close to the small pieces of paper, they get attracted to it.

The methods of charge transfer can be explained through this example. As we can observe that the charges get transferred to our hand and eventually to the ground.

There are two methods of charge transfer that can take place between two bodies.

• Charging by conduction

• Charging by induction

How Do You Transfer a Charge?

Let’s discuss the techniques of charging here:

a. Charge transfer by Conduction

The charge transfer by conduction procedure contains the procedure of moving a charged particle to a conductive material. 

In this fashion, the charges are traveled from the charged material to the conductor. This process is advantageous for charging conductors.

i. Charge Transfer By Conduction through a Negative Charged Object

Let us consider that a metal sphere possesses a negative charge, as shown in the figure. 

When the charged metal sphere interacts with a neutral object, extra electrons from the sphere transfers onto the neutral object and spreads out equally.

Thus, in the result of this process, the object 2 gains negative charge while the metal sphere is quietly charged but has a lesser amount of electrons.

This procedure of charging by contact is called charging by conduction.

ii. Charge Transfer By Conduction through a Positive Charged Object

We know that a positively charged sphere has additional protons, which means a shortage of electrons. Let us think that there are two objects; one positively charged metal plate and a neutral metal sphere.

When a metal plate possessing a positive charge comes in contact with a metal sphere in a neutral state, the electrons from the neutral sphere get drawn towards the metal plate having a positive charge.

This process continues until the positive charge available on the metal plate becomes reallocated.

b. Charge Transfer By Induction

Induced-charge departure is a shift in the point of electrons in a neutral object that happens when a charged object is carried close to it. Here, charging by induction is the charging of a neutral object by taking another charged object close to it; without any physical contact of the neutral object.

To charge more than one object by induction, a positively charged object can be utilized to induce a charge in a neutral object. You can also practice two objects at the same time to charge the objects permanently.

In sphere A, the electrons are pulled by the positive charge on the balloon. Electrons in sphere B are involved with sphere ‘A’ and shifted. Keep the balloon in position and eliminate sphere B from sphere ‘A’, it makes sphere B a positively charged body permanently.

Charge Transfer By Induction through Positive Charged Object

Take two spheres ‘A’ and ‘B’, contact with each other, as shown in the figure.

If we take a positively charged balloon near the sphere ‘A’, the electrons from sphere B will migrate on the way to sphere A because of the attraction between opposite charges.

Accordingly, the sphere ‘A’ acquires negative charges, and sphere ‘B’ acquires positive charges. The spheres are then detached with the help of an insulating cover i.e., a stand or gloves. When the balloon is detached, the charges in sphere A and B will be reorganized, scattering out evenly.

What is Charge Transfer Complex?

The charge transfer complex is known as the electron recipient or donor complex. The charge complex can be defined as the combination of two or more molecules, or of different parts of a huge molecule where a fraction of electronic charge is transported between the molecular entities.

Charge transfer also occurs sometimes in inorganic metals.

What is Charge Transfer Spectra?

In highly ionic crystals, charge transfer spectra resemble electron transfer between neighboring atoms. It can be divided into a donor or recipient. They are dependent upon whether the metal atom donates or accepts an electron.

The relation between optical and chemical charge transfer progressions is examined to calculate charge transfer spectra.

The word comet is derived from the Greek word kometes, which means long-haired. A small body that is composed of volatile ices and dust particles that are orbiting around the sun is known as a comet. While a comet reaches close to the sun, the ices in comets get sublimate and completely became dust particles. Later, the comets get illuminated and a brighter outflowing atmosphere around the comet nucleus is known as the coma. The dust and gas particles in the coma flow freely into the space and form two tails. One tail of the coma contains molecules and radicals and another tail contains dust particles. 

This article explains the origin of comets, structure, parts of comets with composition and facts of comets in detail. 

Origin of Comets 

Comets are the most spectacular object in the sky. Because they have bright glowing comae and long dust tails and ion tails. Usually, comets in the solar system travel in highly eccentric orbits around the sun in their own orbit. Usually, the motion of the comets is dominated by the gravity of the sun or the gravity of planets in the solar system.

Many scientists researched on comets and found that the comets are the primitive leftover bodies during the period of formation of the solar system. They considered that comets should be the first solid bodies that are formed in solar nebule. Usually, the solar radiations formed in the universe disturb the comets in their orbit. Most of the comets are located 6 astronomical units away from the orbit of Jupiter. And also, most of the comets are located in the distant orbit beyond the planets. Sometimes these comets will undergo physical changes like melting due to the modifications in the solar system. The physical and chemical modified records of the comets have also remained in the solar nebula.

Parts of a Comet 

• The comets in the solar system are mainly composed of four visible parts. These parts of a comet describe the structure of a comet. They are the coma, the nucleus, the ion tail and the dust tail.

• The coma in the comets is found around the nucleus, and can freely escape to the atmosphere, while the comets contact close to the sun. During that time, the volatile ices sublimate, carrying with them dust particles that are intimately mixed with the frozen ices in the nucleus.

• The ion tail in the comets is formed by the volatile gases in the coma. Usually, they get ionized by the ultraviolet photons from the Sun and blown away by the solar wind. Usually, the ion tail of the comets will face exactly away from the sun and shine in bluish colour.  The comets are made up of CO⁺ ions.  

Orbits of Comets

Usually, the comets are different from other bodies in the solar system. Comets also orbit around the sun, which is far more eccentric than the planets and other asteroids. Sometimes, comets will come to a distance of about 50,000 AU, which is a substantial fraction of the distance to the nearest stars. The orbital period of the comets will vary from a few years to millions of years depending on the length of the orbit. The comets with a shorter orbital period will carry the comets inwards of the terrestrial planets like Jupiter and Saturn. Some comets will also contact the interstellar space and passes around the sun on open hyperbolic orbits.

 

Composition and Facts of Comets

Comets in the universe have abandoned water, carbonaceous molecules (CO, CO₂, and hydrocarbons) and silicates. All the compositions are available in the ratio of about 1:1:1. They also contain other ions and dust particles. The core of the comets are made up of an amalgamation of rock, dust, water ice, and frozen carbon dioxide, carbon monoxide, methane, and ammonia. In order to study the appearance of comets, the IAU has implemented new identification methods in 1995. Through this method, it is possible to identify, whether the comets are short periodic orbital or long-period comets. The identification system is much similar to the identification of asteroids.  

Neowise Comet 

The neowise comet is one of the long-period comets, which has a nearly parabolic orbit. This neowise comet was discovered on 27^th March 2020 during the Neowise mission of the Wide-field Infrared Survey Explorer (WISE) space telescope. This comet was located about 2 AU away from the sun and 1.7 Astronomical units away from the Earth. The neowise comet is the brightest comet in the solar system.

Interesting Comets Facts 

1. Usually, comets are known as “dirty snowballs” or “cosmic snowballs”. Because comets are made up of ice, rock, gas and dust.

2. Comets generally take elliptical paths to move around the sun, like the planets. The path of a comet is more away from the planet.

3. The nucleus of a comet has a huge variation in its total mass.

4. When comets are moving around the sun, it has a halo. The solar radiation vaporizes the ice and gas. This halo is known as the comet coma. 

5. Comets will generate ion tail, which is the result of solar wind that blows directly away from the sun. 

6. In our solar system, there are billions of comets. And currently, the astronomers identified more than 3000 comets. 

7. It is possible to view comets in the naked eyes of Earth without the telescope.

This article explained what is a comet, the origin, parts of the space comets, composition and facts of comets and the purpose of a comet in detail. 

Conductivity (or specific conductance) in simple words can be described as the ability of an electrolyte solution to conduct electricity. However, all the solutions are not necessarily electrolytes therefore all the solutions will not conduct electricity. The conductivity is also mentioned as specific conductivity in scientific terms. The conductivity in the SI unit is Siemens per meter (S/m). 

The conductivity measurements are a reliable, fast, and inexpensive way of measuring ionic content in a given solution. This is the reason why it is widely adopted in industrial and environmental applications. For eg, in the water purification systems, the conductivity measurement monitoring gives you a perfect trend of the status of water quality. 

Conductivity Chemistry

The specific conductivity of a solution or electrolyte depends on the concentration of electrolytes in it. Conductivity is nothing but the measurement of the movement of electrolytic ions present in the solution. In many cases as the concentration of the electrolyte increases, after a certain peak point, it becomes neutral. Consider the sodium chloride solution which is a good conductor of electricity, but as there is saturation it becomes inactive. 

Based on strength, two types are classified as strong electrolytes and weak electrolytes. Strong electrolytes are assumed to dissolve completely in water. That means when particular quantities of these electrolytes are dissolved in water, they give peak conductance but if the quantity is increased then it starts reducing its conductance. Weak electrolytes do not dissolve completely in water which means that even the low concentrations will not dissociate fully and the conductance will be below. 

 

Electrical Conductivity 

From an applied electric field forces act upon the electrically charged particles which results in an electrical current. In solid materials, current results due to the flow of electrons which is called electronic conduction. Only electronic conduction exists in all conductors, semiconductors, and many insulated materials. The availability of the number of electrons to contribute to the conduction process decides the electrical conductivity. 

Metals, most of them, are the very good conductor of electricity because of higher free electrons. Electrical conductivity can be defined as the ratio between the current density (J) and the electric field intensity (e) and it is the opposite of the resistivity. Silver is said to have the highest conductivity of any metals: 63 x 106 S/m.    

The Conductivity of Water 

Pure water is not a good conductor of electricity but it increases with the increase in ionic concentrations. Typically the water of different purity shows the different conductivity as follows – 

Seawater – 5 S/m

Distilled water Conductivity – 5.5 10 – 6 S/m  

Conductivity of Drinking water – 0.005 – 0.05 S/m

 

Water TDS and Conductivity  

TDS (total dissolved solids) and EC are quite comparable. It is quite possible to calculate the TDS of water once you measure the conductivity of water. Thus we can know the TDS of distilled water or drinking water if we measure the conductivity of drinking water and distilled water conductivity. 

TDS is a measure of total ions in the solution and EC is a measure of the ionic activity of a solution, so it is quite relevant to each other. TDS of water can be calculated if we measure conductivity, by following the formula – 

TDS (mg/l) = 0.5 x EC (dS/m or mho/cm) or 0.5 X 1000 x EC (ms/cm)

The unit of measurement of TDS is micro siemens or ppm (parts per million)

The water conductivity meter is widely used to measure the conductivity of water. In recent times, there is no need to apply a formula to calculate TDS as the conductivity meter has the dual function of displaying both TDS and conductivity. 

As the concentration of the solution increases (EC >2000 or TDS >1000), the bonding of ions to each other increases, and this tends to decrease their activity and result in the reduction in carrying current. As TDS goes higher the ratio of TDS/EC gets saturated to TDS = 0.9 x EC. This tends to deviate from the TDS and EC relationship and the sample has to be treated differently.

The measurement of water conductivity with help of a water conductivity meter helps in a lot of fields like manufacturing, agriculture, irrigation, etc. the quality of water plays an important role in these industries to maintain the appropriate quality of the products and crops. In the case of irrigation and agriculture, the values of EC and TDS are related to each other and is converted to the accuracy of about 10% – 

TDS (mg/l) = 640 x EC (ds/m or mho/cm). In manufacturing industries such as food industries and especially in water and beverage manufacturing, the quality of water is monitored and maintained as per regulations. This also helps the manufacturers to keep their products of uniform taste all over. 

As the water parameters and taste differ from place to place the product taste also might differ vastly which will impact the brand. Thus in maintaining the uniform quality, TDS and conductivity play an important role as these are very basic characteristics of water. 

In the packaged drinking water section, the water quality is maintained by the application of the reverse osmosis process which again enhances the water quality in terms of TDS and EC. In the reverse osmosis process, the water is pressurized through a semipermeable membrane that leaves the impurities behind. With the RO process, around 95-99% of TDS is removed and gives highly purified water.

Have you ever thought about the importance of taking measurements? Taking measurements is one of the important, common, and daily activities of our day-to-day life. We can’t imagine spending a day without measuring anything. Without measurements, the world would have been complete chaos.

It is an integral part of our daily routine. Starting from Cooking, where a measured amount of ingredients are added to cook food properly; purchasing items so that fixed amounts can be allocated to certain objects medicines, in which a fixed dosage is required to treat a particular disease, to decide the winner among the participants, etc.

Today, we follow a standard unit of measurements for length, mass, volume, and time. But have ever wondered how these measurements were taken when such units did not come into existence.

Length

In early days, the human body was used to provide the basis for units of length

• Inch: It was used to measure the length of items small in size, for example, the seam of a cloth, length of the paper, etc. Inch is the measure of the human thumb.

• Foot: Foot is defined as the measure of length 15.3 % of the height of a human body with an average height of 160 cm. This unit differed from place to place and trade to trade. This unit was preferred by Roman and Greeks and was mainly used to calculate the size of a piece of cloth, the height of human beings and cattle, the size of a building, etc.

• Cubit: Cubit is the unit of measurement of length based on the length of the forearm, from the tip of the middle finger to the elbow bottom. It was preferred by Egyptians and Mesopotamians. Cubit rods have been discovered in the remains of the ancient Egyptian civilization. Usually, these rods are 20 inches in length, which are divided into seven palms; each palm is further divided into four fingers which are further subdivided.

• Yard: Yard is the unit of distance, which is based on human paces. A yard is equivalent to two cubits or three feet, which is approximately 36 inches. The early yard was divided by the binary method into 2, 4, 8, and 16 parts called the half-yard, span, finger, and nail Miles.

A foot comprises 12 inches and three feet comprise a yard. Such measurements as these, it was easy to explain how far the next village was and to find out whether an object will get through a doorway.

Weight

• In early times, to measure weight the grains of wheat or barleycorn were used because of their approximate standard size. The barleycorn was used to weigh the precious metals silver and gold. Large units preserved in stone standards were developed that were used as both units of mass and monetary currency. The standard unit was taken to the number of grains of wheat. This is even now being used by some jewellers. 64.79891 milligrams sums up to make one grain.

Time

• Sundial: The movement of the sun in the sky was used to estimate time, which was done based on the length and position of the shadow cast by a vertical stick. Then the marks were made where the sun’s shadow fell, which gave an approximate measure of time of the day consistently. The device came to be called a sundial.

• Hourglass: To estimate the time, this device is used. The hourglass works on the same principle followed by a water clock. It uses sand instead of water. It is still found in some places, in a reduced form, and also in use. It has two vertically connected glass bulbs that allow a regulated flow of a substance from the upper bulb to the lower one.

The upper and lower bulbs are kept symmetric so that the hourglass will measure the same duration regardless of orientation. There are various factors that contribute for the calculation of the specific duration of time. These include the quantity and coarseness of the particulate matter, the bulb size, etc.