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Tuesday, 29 October 2024

System of Units

 

A system of units is a collection of units in which certain units are chosen as fundamental and all others are derived from them. This system is also called an absolute system of units. In most systems, the mass, length, and time are considered to be fundamental quantities, and their units are called fundamental units. The following are some systems of units which are in common use.

·         c.g.s. system of units: The unit of length is centimetre (cm). The unit of mass is gram (g). The unit of time is second (s)

·         m.k.s. system of units: The unit of length is the metre (m). The unit of mass is the kilogram (kg). The unit of time is second (s)

·         f.p.s. system of units: The unit of length is a foot (ft). The unit of mass is a pound (Lb). The unit of time is second (s). This system is no more in use. This system is also known as Imperial system or the British Imperial system. Temperature is measured in Fahrenheit.

 S.I. System of Units:

In the year 1960, the Eleventh General Conference of Weights and Measures introduced the International System of Units. The International Standard Organization (ISO) and the International Electrochemical Commission endorsed the system in 1962.  In October 1971 a replacement of the metric system of units was done with a new system called Systeme Internationale d’ Unites. The International System of Units, commonly known as the SI system, is the modern form of the metric system and is the most widely used system of measurement in the world. It provides a standard and coherent set of units for expressing physical quantities.


Fundamental Units:

Fundamental Quantity

S.I. Unit

Symbol

1

Length

Metre

m

2

Mass

Kilogram

kg

3

Time

Second

s

4

Temperature

Kelvin

K

5

Electric current

Ampere

A

6

Luminous intensity

Candela

cd

7

Amount of substance

mple

mol

Besides these seven basic units, there are two supplementary units. S.I. unit for the plane angle is radian (rad) and that of solid angle is steradian (sd).

Supplementary Units:

Quantity

S.I. Unit

Symbol

1

Plane angle

radian

rad

2

Solid angle

steradian

sr

This system of units is an improvement and extension of the traditional metric system. Now, this system of units has replaced all other systems of units in all branches of science, engineering, industry, and technology.

Guidelines for Writing SI Units and Their Symbols:

·         All units and their symbols should be written in small case letters e.g. centimetres (cm), metre (m), kilogram per metre cube ( kg m-3).

·         The units named after scientists are not written with a capital initial letter but its symbol is written in capital letter. Thus the unit of force is written as ‘newton’ or’ N’ and not as ‘Newton’. Similarly unit of work and energy is joule (J), S.I. unit of electric current is ampere (A). The S.I. nit of pressure is pascal (Pa) and that of temperature is kelvin (K).

·         No full stop should be placed after the symbol.

·         The denominators in a compound unit should be written with negative powers. Thus an index notation should be used to write a derived unit. for example unit of velocity should be written as ms-1 instead of m/s. The unit of density is kilogram per metre cube ( kg m-3 and not kg/m3)

·         No plural form of a unit or its symbol should be used. example 5 newtons should be written as 5 N and not as 5 Ns.

·         A compound unit obtained from units of two or more physical quantities is written either by putting a dot or leaving a space between symbols of two units. Example unit of torque is newton metre is written as Nm ot N.m. Unit of impulse is newton second is written as N s or N.s.

·         Some space should be maintained between the number and its unit

Advantages of S.I. System of Units:

·         Units are simple to express

·         This system uses only one unit for one physical quantity. Hence it is a rational system of units.

·         Units of many physical quantities are related to each other through simple and elementary relationships   For example 1 ampere = 1 volt / 1 ohm.

·         It is a metric system of units. There is a decimal relationship between the units of the same quantity and hence it is possible to express any small or large quantity as a power of 10. i.e. inter-conversion is very easy.    For e.g. 1kg   =  1000 gm  = 10³ gm

·         The physical quantities can be expressed in terms of suitable prefixes.

·         a joule is a unit of all forms of energy and it is a unit of work. Hence it forms a link between mechanical and electrical units. Hence S.I. the system is a rational system because it uses only one unit for one physical quantity.

·         This system forms a logical and interconnected framework for all measurements in science, technology, and commerce.

·         All derived units can be obtained by dividing and multiplying the basic and supplementary units and no numerical factors are introduced as in another system of units. Hence S.I. system of units is a coherent system. Hence S.I. system of units is used worldwide.

General Steps to Find Derived Unit:

·         Step -1 Write the formula for the quantity whose unit is to be derived.

·         Step -2 Substitute units of all the quantities in one system of units in their fundamental or standard form.

·         Step -3 Simplify and obtain derive unit of the quantity.

Example: To find the unit of velocity.

Velocity is a derived quantity. Hence its unit is a derived unit.

The velocity is given by, velocity = displacement/time

S.I. unit of velocity = S.I. unit of displacement/ S.I. unit of time = m/s

Thus S.I. unit of velocity is m/s

Definitions of Fundamental Units in S. I. System:

1 metre:

·         The unit of length is a metre.  Its symbol is ‘m’.

·         The distance travelled by electromagnetic waves in the vacuum in 1/299, 792, 458 seconds is called 1 metre. The denominator is the velocity of light in the vacuum which is in m/s and is known accurately.

·         One metre is 1,650, 763.73 times the wavelength of orange light emitte by a krypton atom at normal pressure. The wavelength of light is precisely defined in terms of electron transition in an atom, is easily reproducible and is not affected by the change in place, time, temperature and pressure, etc. Hence metre is defined in terms of wavelength of orange light.

1 kilogram:

·         The unit of mass is a kilogram.  Its symbol is ‘kg’.

·         1 kilogram is defined is the total mass of 5.0188 × 1025 atoms of C12 isotopes of carbon. Or The mass of a cylinder made up of platinum-iridium alloy kept at the International Beuro of Weights and Measure is defined as 1 kilogram. Reason for Using Platinum iridium alloy for the cylinder is that it is least affected by environment and time.

1 second:

·         The unit of time is second. Its symbol is ‘s’.

·         1 second is a time duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the Cesium-133 atom. Period of vibration of the atom of Cesium – 133  is used for defining the standard of time because the period of vibration of the atom of Cesium – 133 are precisely defined, is easily reproducible and is not affected by a change in place, time, temperature and pressure, etc.

1-degree kelvin:

·         The unit of temperature is degree kelvin. Its symbol is ‘K’.

·         1-degree kelvin is a fraction 1/ 273.16 of the thermodynamic temperature of the triple point of the water. The triple point of the water is a temperature at which ice, water, and water vapour are in equilibrium.

1 candela:

·         The unit of luminous intensity is candela. Its symbol is ‘cd’.

·         1 candela is luminous intensity in the normal direction of a surface of area 1/600000 m2 of a black body at the freezing point of platinum under pressure of 1.01325 × 105 N/m2.

1 ampere:

·         The unit of electric current is the ampere. Its symbol is ‘A’.

·         1 ampere is the constant current, which is maintained in each of two infinitely long straight parallel conductors of a negligible cross-section, situated one metre apart in vacuum, will produce between the conductors a force of 2 × 10-7 N/m.

1 mole:

·         The unit of the amount of substance is mole. Its symbol is ‘mol’

·         1 mole is the amount of substance which contains as many elementary entities (atoms, molecules, ions, electrons, etc.) as there are atoms in 0.012 kg of pure C12. The number of entities in one mole is 6.02252 X 1023. It is called as Avagadro’s number.

1 radian:

·         The unit of plane angle is the radian. Its symbol is ‘rad’

·         One radian is defined as the angle subtended at the centre of a circle by an arc equal in length to the radius of the circle.

1 steradian:

·         The unit of solid angle is steradian. Its symbol is ‘sr’

·         One steradian is defined as the solid angle that encloses a surface on the sphere of an area equal to the square of its radius.

·         Maintaining Uniformity of Standards

An international body Conference Generale des Poids et Measures or CGPM (General Conference of Weight and Measures) has been given the authority to decide the standards and units by international agreement. It holds its meetings and any change in the standard units are communicated through the publications of the Conference.

India adopted the metric system of units in 1956 by Parliament Act “Weights and Measures Act- 1956”. The function of manufacturing, maintaining, monitoring, and improving the standards of measurements is discharged by the National Physical Laboratory (NPL), New Delhi. The uniformity in standards is maintained as follows:

·         Measures (e.g. balances and weights) used by shopkeepers are expected to be certified by the Department of Measures and Weights of the local government.

·         The working standards of these local departments have to be calibrated against the state-level standards, or any laboratory which is entitled to do so.

·         The state-level laboratories are required to get their standards calibrated from the National Physical Laboratory at the national level, which is equivalent to international standards. Thus, measurements made at any place in the world are connected with the international system.

Prefixes Used in SI System:


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Sunday, 27 October 2024

 Determination of pH of drinking waterApparatus and equipment: pH meter, reference electrode, sensor (glass) electrode, beakers, stirrer. Reagents and standards: pH 4 buffer solution, pH 7 buffer solution, pH 9.2 buffer solution.
















Principle

The pH is determined by measurement of the electromotive force (emf) of a cell comprising of an indicator electrode (an electrode responsive to hydrogen ions such as glass electrode) immersed in the test solution and a reference electrode (usually a calomel electrode). Contact is achieved by means of a liquid junction, which forms a part of the reference electrode. The emf of this cell is measured with pH meter. Since the pH is defined operationally on a potentiometric scale, the measuring instrument is also calibrated potentiometrically with an indicating (glass) electrode and a reference electrode using standard buffers having assigned pH value so that

PHB-log₁₀ [H⁺]

Where  pH = assigned pH of standard buffer. The operational pH scale is used to measure sample pH and

pHs=pHB+ F (Es-EB)/2.303 RT

nowhere, pHs = potentiometrically measured sample pH

F= Faraday 9.649 x 104 coulomb/mole

=Es= Sample emf, V

EB = Buffer emf, V

R = Gas constant = 1.987 cal deg¹ mole¹

T= absolute temperature, “K is defined as:

Procedure

(a) Before use, remove electrodes from storage solutions (recommended by the

Manufacturer) and rinse with distilled water.

(b) Dry electrodes by gently blotting with a soft tissue paper, standardize instrument With electrodes immersed in a buffer solution within 2 pH units of sample pH.

 (c) Remove electrodes from the buffer, rinse thoroughly with distilled water and blot dry.

(d) Immerse in a second buffer below pH 10, approximately 3 pH units different from the first, the reading should be within 0.1 unit for the pH of the second buffer. (If the meter response shows a difference greater than 0.1 pH unit from the expected value, look for trouble with the electrodes or pH meter) and sample by

(e) For sample analysis, establish equilibrium between electrodes stirring sample to ensure homogeneity and measure pH.

(f) For buffered samples (or those with high ionic strength), condition the electrodes. after cleaning by dipping them into the same sample, and read pH.

g) With poorly buffered solutions (dilute), equilibrate electrodes by immersing in three or four successive portions of samples. Take a fresh sample and record the pH.

The pH value is obtained directly from the instrument

                   Scope of Error

1. The precision and accuracy attainable with a given pH meter will depend on the type and condition of the instrument and the care used in standardization an operation.

2. Guard against possible erratic results arising from mechanical or electrical failures-weak batteries, dam aged electrodes, plugged liquid junctions, and fouling of electrodes.

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सिद्धांत: पीएच का निर्धारण एक सेल के इलेक्ट्रोमोटिव बल (ईएमएफ) के माप से किया जाता है जिसमें परीक्षण समाधान में डूबे एक संकेतक इलेक्ट्रोड (हाइड्रोजन आयनों जैसे ग्लास इलेक्ट्रोड के लिए उत्तरदायी इलेक्ट्रोड) और एक संदर्भ इलेक्ट्रोड (आमतौर पर एक कैलोमेल इलेक्ट्रोड) शामिल होता है। संपर्क एक तरल जंक्शन के माध्यम से प्राप्त किया जाता है, जो संदर्भ इलेक्ट्रोड का एक हिस्सा बनता है। इस सेल का ईएमएफ पीएच मीटर से मापा जाता है। चूंकि पीएच को पोटेंशियोमेट्रिक पैमाने पर क्रियात्मक रूप से परिभाषित किया जाता है, इसलिए मापने वाले उपकरण को निर्दिष्ट पीएच मान वाले मानक बफ़र्स का उपयोग करके एक संकेत (ग्लास) इलेक्ट्रोड और एक संदर्भ इलेक्ट्रोड के साथ पोटेंशियोमेट्रिक रूप से कैलिब्रेट किया जाता है ताकि
पीएचबी-लॉग10 [एच+]
 
जहां पीएच = मानक बफर का निर्दिष्ट पीएच। परिचालन पीएच स्केल का उपयोग नमूना पीएच को मापने के लिए किया जाता है
pHs=pHB+ F (Es-EB)/2.303 RT
कहीं नहीं, पीएच = पोटेंशियोमेट्रिक रूप से मापा गया नमूना पीएच
एफ= फैराडे 9.649 x 104 कूलम्ब/मोल
=Es=नमूना ईएमएफ, वी
ईबी = बफर ईएमएफ, वी
आर = गैस स्थिरांक = 1.987 कैल डे¹ मोल¹
टी = पूर्ण तापमान, "के को इस प्रकार परिभाषित किया गया है: 
प्रक्रिया:- ए) उपयोग से पहले, भंडारण समाधान से इलेक्ट्रोड हटा दें (अनुशंसित)।
निर्माता) और आसुत जल से कुल्ला करें।
(बी) नरम टिशू पेपर से धीरे से सोखकर इलेक्ट्रोड को सुखाएं, नमूना पीएच के 2 पीएच इकाइयों के भीतर बफर समाधान में इलेक्ट्रोड को डुबोकर उपकरण को मानकीकृत करें।
 (सी) बफर से इलेक्ट्रोड निकालें, आसुत जल से अच्छी तरह धोएं और सुखाएं।
(डी) पीएच 10 से नीचे दूसरे बफर में डुबोएं, पहले से लगभग 3 पीएच इकाइयां अलग, दूसरे बफर के पीएच के लिए रीडिंग 0.1 यूनिट के भीतर होनी चाहिए। (यदि मीटर प्रतिक्रिया अपेक्षित मान से 0.1 पीएच इकाई से अधिक अंतर दिखाती है, तो इलेक्ट्रोड या पीएच मीटर में समस्या देखें) और नमूना लें
(ई) नमूना विश्लेषण के लिए, एकरूपता सुनिश्चित करने और पीएच मापने के लिए नमूने को हिलाने वाले इलेक्ट्रोड के बीच संतुलन स्थापित करें।
(एफ) बफ़र किए गए नमूनों (या उच्च आयनिक शक्ति वाले) के लिए, इलेक्ट्रोड को कंडीशन करें। इन्हें एक ही नमूने में डुबोकर साफ करने के बाद पीएच पढ़ें।
छ) खराब बफर समाधान (पतला) के साथ, नमूनों के तीन या चार क्रमिक भागों में डुबो कर इलेक्ट्रोड को संतुलित करें। एक ताजा नमूना लें और पीएच रिकॉर्ड करें
                  त्रुटि का दायरा
               

               पीने के पानी के पी०एच० {pH} का निर्धारण


उपकरण: पी०एच० मीटर, संदर्भ इलेक्ट्रोड, सेंसर (ग्लास) इलेक्ट्रोड, बीकर, स्टिरर। अभिकर्मक {REAGENTS} और {Standards } मानक: पी०एच० 4 बफर समाधान, पी०एच० 7 बफर समाधान, पी०एच० 9.2 बफर समाधान।
सिद्धांत: पीएच का निर्धारण एक सेल के इलेक्ट्रोमोटिव बल (ईएमएफ) के माप से किया जाता है जिसमें परीक्षण समाधान में डूबे एक संकेतक इलेक्ट्रोड (हाइड्रोजन आयनों जैसे ग्लास इलेक्ट्रोड के लिए उत्तरदायी इलेक्ट्रोड) और एक संदर्भ इलेक्ट्रोड (आमतौर पर एक कैलोमेल इलेक्ट्रोड) शामिल होता है। संपर्क एक तरल जंक्शन के माध्यम से प्राप्त किया जाता है, जो संदर्भ इलेक्ट्रोड का एक हिस्सा बनता है। इस सेल का ईएमएफ पीएच मीटर से मापा जाता है। चूंकि पीएच को पोटेंशियोमेट्रिक पैमाने पर क्रियात्मक रूप से परिभाषित किया जाता है, इसलिए मापने वाले उपकरण को निर्दिष्ट पीएच मान वाले मानक बफ़र्स का उपयोग करके एक संकेत (ग्लास) इलेक्ट्रोड और एक संदर्भ इलेक्ट्रोड के साथ पोटेंशियोमेट्रिक रूप से कैलिब्रेट किया जाता है ताकि
पीएचबी-लॉग10 [एच+]

जहां पीएच = मानक बफर का निर्दिष्ट पीएच। परिचालन पीएच स्केल का उपयोग नमूना पीएच को मापने के लिए किया जाता है
pHs=pHB+ F (Es-EB)/2.303 RT
कहीं नहीं, पीएच = पोटेंशियोमेट्रिक रूप से मापा गया नमूना पीएच
एफ= फैराडे 9.649 x 104 कूलम्ब/मोल
=Es=नमूना ईएमएफ, वी
ईबी = बफर ईएमएफ, वी
आर = गैस स्थिरांक = 1.987 कैल डे¹ मोल¹
टी = पूर्ण तापमान, "के को इस प्रकार परिभाषित किया गया है: 
प्रक्रिया:- ए) उपयोग से पहले, भंडारण समाधान से इलेक्ट्रोड हटा दें (अनुशंसित)।
निर्माता) और आसुत जल से कुल्ला करें।
(बी) नरम टिशू पेपर से धीरे से सोखकर इलेक्ट्रोड को सुखाएं, नमूना पीएच के 2 पीएच इकाइयों के भीतर बफर समाधान में इलेक्ट्रोड को डुबोकर उपकरण को मानकीकृत करें।
 (सी) बफर से इलेक्ट्रोड निकालें, आसुत जल से अच्छी तरह धोएं और सुखाएं।
(डी) पीएच 10 से नीचे दूसरे बफर में डुबोएं, पहले से लगभग 3 पीएच इकाइयां अलग, दूसरे बफर के पीएच के लिए रीडिंग 0.1 यूनिट के भीतर होनी चाहिए। (यदि मीटर प्रतिक्रिया अपेक्षित मान से 0.1 पीएच इकाई से अधिक अंतर दिखाती है, तो इलेक्ट्रोड या पीएच मीटर में समस्या देखें) और नमूना लें
(ई) नमूना विश्लेषण के लिए, एकरूपता सुनिश्चित करने और पीएच मापने के लिए नमूने को हिलाने वाले इलेक्ट्रोड के बीच संतुलन स्थापित करें।
(एफ) बफ़र किए गए नमूनों (या उच्च आयनिक शक्ति वाले) के लिए, इलेक्ट्रोड को कंडीशन करें। इन्हें एक ही नमूने में डुबोकर साफ करने के बाद पीएच पढ़ें।
छ) खराब बफर समाधान (पतला) के साथ, नमूनों के तीन या चार क्रमिक भागों में डुबो कर इलेक्ट्रोड को संतुलित करें। एक ताजा नमूना लें और पीएच रिकॉर्ड करें।
                        त्रुटि का दायरा

1. किसी दिए गए पीएच मीटर के साथ प्राप्त होने वाली परिशुद्धता और सटीकता उपकरण के प्रकार और स्थिति और किसी ऑपरेशन के मानकीकरण मे

                                       

Hardness of Water

   Hardness of Water

your water’s hardness based on these concentrations of calcium carbonate: Below 75 mg/L – is generally considered soft. 76 to 150 mg/L – moderately hard. 151 to 300 mg/L

Water hardness or softness is measured using grains per gallon (gpg), where one grain is equal to 0.002 ounces of calcium carbonate dissolved in 1 gallon of water. 0–3 gpg is considered soft water. 3.5–7 gpg is considered moderate and ideal

Harter is considered soft if total hardness is less than 75 ppm, moderately hard at 75 to 150 ppm, hard at 150 to 300 ppm, and very hard at 300 ppm or higher

In drdness is a measure of the magnesium, calcium, and carbonate minerals in water. Wainking-water, hardness is in the range 10–500 mg of calcium carbonate per litre

he hardness of water is mainly contributed by calcium and magnesium ions. The hardness of water is defined as total parts per million (ppm) of CaCO3 by weight. For example, the hardness of water 10 ppm means 10 g of CaCO3 in one million grams of water or 0.01 g of CaCO3 in 1-L water.

Total dissolved solids of Ca++ and Mg++ in soft water should be up to 200 ppm. Soft water is used for drinking water. Water used for drinking is unpalatable if the TDS level of it is above 500 ppm. As per standards, the acceptable limit of TDS is 200ppm

emporary hardness can be removed by boiling, but permanent hardness cannot be removed with this method. Water softening at home can be done using a resin coated with sodium. Other methods of removing hardness include Clark’s process, Calgon’s process, and ion-exchange resin.

The amount of hardness is expressed in milligrams per litre (mg/L) or grains per gallon (gpg) as calcium carbonate. Hardness is calculated from the equation Hardness = 2.497 (Ca) + 4.118 (Mg). Therefore, fluctuations in the magnesium pool affect hardness stronger than do calcium fluctuations

Understanding Water Hardness Levels In Your Home Water. The Short Answer Is: A good water hardness level for your home typically falls between 3.5 and 7 grains per gallon. Water within this range is considered modera

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