উইকিপিডিয়া

আপেক্ষিক গুরুত্ব: সংশোধিত সংস্করণের মধ্যে পার্থক্য

ইতিহাস ব্রাউজ করুন
← পূর্বের পার্থক্যপরবর্তী পার্থক্য →
বিষয়বস্তু বিয়োগ হয়েছে বিষয়বস্তু যোগ হয়েছে
দৃশ্যমানউইকিপাঠ্য
SushmitaSwarna (আলোচনা | অবদান)
৫৩৮টি সম্পাদনা
সম্পাদনা সারাংশ নেই
SushmitaSwarna (আলোচনা | অবদান)
৫৩৮টি সম্পাদনা
সম্পাদনা সারাংশ নেই
২৭ নং লাইন:
যেখানে, ''g'' স্থানীয় মহাকর্ষীয় ত্বরণ, ''V'' নমুনা বস্তু ও পানির আয়তন (উভয়ের জন্য একই), ''ρ''<sub>sample</sub> নমুনা বস্তুর ঘনত্ব, ''ρ''<sub>H<sub>2</sub>O</sub> পানির ঘনত্ব এবং ''W''<sub>V</sub> দ্বারা শূন্যস্থানে নমুনা বস্তুর ওজন নির্দেশ করে।
 
পানির ঘনত্ব তাপমাত্রা ও চাপের পরিবর্তনের সাথে পরিবর্তিত হয় এবং তা নমুনা বস্তুর ঘনত্বের ক্ষেত্রেও ঘটে। ঘনত্ব বা ওজন নির্ণয়ের ক্ষেত্রে তাপমাত্রা ও চাপ উল্লেখ করা প্রয়োজন। প্রায় সকল ক্ষেত্রেই প্রমাণ বায়ুমণ্ডলীয় চাপে মান নেয়া হয় (১০১.৩২৫ কিলোপ্যাসকেল ± আবহাওয়ার পরিবর্তনের ফলে পার্থক্য)। কিন্তু যেহেতু অধিকাংশ ক্ষেত্রে আপেক্ষিক গুরুত্ব অসংকোচনীয় জলীয় দ্রবণ বা অন্যান্য অসংকোচনীয় পদার্থের জন্য পরিমাপ করা হয় (যেমন পেট্রোলিয়াম), তাই অন্তত আপাত আপেক্ষিক গুরুত্ব নির্ণয়ের ক্ষেত্রে চাপের পার্থক্যের জন্য ঘনত্বের তারতম্য উপেক্ষা করা যেতে পারে। প্রকৃত (''শূন্যস্থানে'') আপেক্ষিক গুরুত্ব পরিমাপের ক্ষেত্রে বায়ুমণ্ডলীয় চাপ অবশ্যই পরিমাপ করা আবশ্যক (নিচে দেখুন)। (''T''<sub>s</sub>/''T''<sub>r</sub>) রাশি দ্বারা তাপমাত্রা প্রকাশ করা হয়, যেখানে ''T''<sub>s</sub> রাশি দ্বারা নমুনা বস্তুর ঘনত্ব নির্ণয়ের সময় তাপমাত্রা আর ''T''<sub>r</sub> রাশি দ্বারা প্রসঙ্গ বস্তুর(পানি) ঘনত্ব নির্ণয়ের সময়ের তাপমাত্রা। উদাহরণস্বরূপ, SG (২০°সে/৪°C) দ্বারা বোঝায় যে নমুনা বস্তুর ঘনত্ব ২০°সে তাপমাত্রায় আর পানির ঘনত্ব ৪°সে তাপমাত্রায় নির্ণয় করা হয়েছে। Takingবিভিন্ন intoনমুনা accountও differentতাপমাত্রার sampleকথা andমাথায় reference temperaturesরেখে, weআমরা noteদেখতে thatপারি যে, while ''SG''<sub>H<sub>2</sub>O</sub> = {{val|1.000000}} (20২০&nbsp;°Cসে/20২০&nbsp;°Cসে), it= is১.০০০ also০০০ the caseহলেও, thatএটিও বাস্তব যে ''SG''<sub>H<sub>2</sub>O</sub> (২০&nbsp;°সে/৪&nbsp;°সে) = {{frac|{{val|0.998203}}|{{val|0.999840}}}} = {{val|0.998363}} (20&nbsp;°C/4&nbsp;°C).। Hereএখানে, temperature is being specified using the current [[ITS-90]] scale and the densities<ref>Bettin, H.; Spieweck, F.: "Die Dichte des Wassers als Funktion der Temperatur nach Einführung des Internationalen Temperaturskala von 1990" PTB-Mitteilungen 100 (1990) pp. 195–196</ref> used here and in the rest of this article are based on that scale. On the previous IPTS-68 scale, the densities at 20২০&nbsp;°Cসে and 4৪&nbsp;°Cসে are {{val|0.9982071}} and {{val|0.9999720}} respectively, resulting in an SG (20২০&nbsp;°Cসে/4৪&nbsp;°Cসে) value for water of {{val|0.9982343}}.
 
As the principal use of specific gravity measurements in industry is determination of the concentrations of substances in aqueous solutions and as these are found in tables of SG versus concentration, it is extremely important that the analyst enter the table with the correct form of specific gravity. For example, in the brewing industry, the [[Plato scale|Plato table]] lists sucrose concentration by weight against true SG, and was originally (20&nbsp;°C/4&nbsp;°C)<ref>ASBC Methods of Analysis Preface to Table 1: Extract in Wort and Beer, American Society of Brewing Chemists, St Paul, 2009</ref> i.e. based on measurements of the density of sucrose solutions made at laboratory temperature (20&nbsp;°C) but referenced to the density of water at 4&nbsp;°C which is very close to the temperature at which water has its maximum density ''ρ''<sub>H<sub>2</sub>O</sub> equal to 999.972&nbsp;kg/m<sup>3</sup> in [[International System of Units|SI units]] ({{val|0.999972|u=g/cm<sup>3</sup>}} in [[CGS system|cgs units]] or 62.43&nbsp;lb/cu&nbsp;ft in [[United States customary units]]). The [[American Society of Brewing Chemists|ASBC]] table<ref>ASBC Methods of Analysis ''op. cit.'' Table 1: Extract in Wort and Beer</ref> in use today in North America, while it is derived from the original Plato table is for apparent specific gravity measurements at (20&nbsp;°C/20&nbsp;°C) on the IPTS-68 scale where the density of water is {{val|0.9982071|u=g/cm<sup>3</sup>}}. In the sugar, soft drink, honey, fruit juice and related industries sucrose concentration by weight is taken from a table prepared by [[Brix|A. Brix]] which uses SG (17.5&nbsp;°C/17.5&nbsp;°C). As a final example, the British SG units are based on reference and sample temperatures of 60&nbsp;°F and are thus (15.56&nbsp;°C/15.56&nbsp;°C).
 
Given the specific gravity of a substance, its actual density can be calculated by rearranging the above formula:
 
:<math>{\rho_\text{substance}} = SG \times \rho_\mathrm{H_2O}.</math>
==Examples==
*[[Helium]] gas has a density of 0.164&nbsp;g/L;<ref name="UCSB">[http://web.physics.ucsb.edu/~lecturedemonstrations/Composer/Pages/36.39.html UCSB]</ref> it is 0.139 times as dense as [[air]].
*[[Air]] has a density of 1.18&nbsp;g/L.<ref name="UCSB"/>
 
Occasionally a reference substance other than water is specified (for example, air), in which case specific gravity means density relative to that reference.
{{Specific gravity}}
 
*[[Urine]]==Measurement: normallyapparent hasand atrue specific gravity between 1.003 and 1.035.==
===Pycnometer===
*[[Blood]] normally has a specific gravity of approximately 1.060.
*[[Vodka]] 80° proof (40% v/v) has a specific gravity of 0.9498.<ref name="Cocktail Specific Gravities">[http://www.goodcocktails.com/bartending/specific_gravity.php Table of liqueurs Specific Gravity]</ref>
 
Specific gravity can be measured in a number of value ways. The following illustration involving the use of the [[pycnometer]] is instructive. A pycnometer is simply a bottle which can be precisely filled to a specific, but not necessarily accurately known volume, ''V''. Placed upon a balance of some sort it will exert a force.
==See also==
 
:<math> F_\mathrm{b} = g\left(m_\mathrm{b} - \rho_\mathrm{a}\frac{m_\mathrm{b}}{\rho_\mathrm{b}}\right) </math>
 
where ''m''<sub>b</sub> is the mass of the bottle and ''g'' the [[gravitational acceleration]] at the location at which the measurements are being made. ''ρ''<sub>a</sub> is the density of the air at ambient pressure and ''ρ''<sub>b</sub> is the density of the material of which the bottle is made (usually glass) so that the second term is the mass of air displaced by the glass of the bottle whose weight, by [[Archimedes' principle#Archimedes' principle|Archimedes Principle]] must be subtracted. The bottle is filled with air, but as that air displaces an equal amount of air the weight of that air is canceled by the weight of the air displaced. Now we fill the bottle with the reference fluid, for example pure water. The force exerted on the pan of the balance becomes:
 
:<math> F_\mathrm{w} = g\left(m_\mathrm{b} - \rho_\mathrm{a}\frac{m_\mathrm{b}}{\rho_\mathrm{b}} + V\rho_\mathrm{w} - V\rho_\mathrm{a}\right). </math>
 
If we subtract the force measured on the empty bottle from this (or tare the balance before making the water measurement) we obtain.
 
:<math>F_\mathrm{w,n} = gV( \rho_\mathrm{w} - \rho_\mathrm{a}) </math>
 
where the subscript n indicates that this force is net of the force of the empty bottle. The bottle is now emptied, thoroughly dried and refilled with the sample. The force, net of the empty bottle, is now:
 
:<math>F_\mathrm{s,n} = gV(\rho_\mathrm{s} - \rho_\mathrm{a}) </math>
 
where ''ρ''<sub>s</sub> is the density of the sample. The ratio of the sample and water forces is:
 
:<math>SG_\mathrm{A} = \frac{gV(\rho_\mathrm{s} - \rho_\mathrm{a})}{gV( \rho_\mathrm{w} - \rho_\mathrm{a})} = \frac{ \rho_\mathrm{s} - \rho_\mathrm{a} }{ \rho_\mathrm{w} - \rho_\mathrm{a}}. </math>
 
This is called the Apparent Specific Gravity, denoted by subscript A, because it is what we would obtain if we took the ratio of net weighings in air from an analytical balance or used a [[hydrometer]] (the stem displaces air). Note that the result does not depend on the calibration of the balance. The only requirement on it is that it read linearly with force. Nor does ''SG''<sub>A</sub> depend on the actual volume of the pycnometer.
 
Further manipulation and finally substitution of ''SG''<sub>V</sub>, the true specific gravity (the subscript V is used because this is often referred to as the specific gravity ''in vacuo''), for {{sfrac|''ρ''<sub>s</sub>|''ρ''<sub>w</sub>}} gives the relationship between apparent and true specific gravity.
 
:<math>SG_\mathrm{A}= \frac{\frac{\rho_\mathrm{s}}{\rho_\mathrm{w}}-\frac{\rho_\mathrm{a}}{\rho_\mathrm{w}} }{ 1 - \frac{\rho_\mathrm{a}}{\rho_\mathrm{w}}} =\frac{SG_\mathrm{V}-\frac{\rho_\mathrm{a}}{\rho_\mathrm{w}} }{ 1 - \frac{\rho_\mathrm{a}}{\rho_\mathrm{w}}}</math>
 
In the usual case we will have measured weights and want the true specific gravity. This is found from
 
:<math>SG_\mathrm{V} = SG_\mathrm{A} - \frac{\rho_\mathrm{a}}{\rho_\mathrm{w} }\left(SG_\mathrm{A}-1\right).</math>
 
Since the density of dry air at 101.325&nbsp;kPa at 20&nbsp;°C is<ref>DIN51 757 (04.1994): Testing of mineral oils and related materials; determination of density</ref> {{val|0.001205|u=g/cm<sup>3</sup>}} and that of water is {{val|0.998203|u=g/cm<sup>3</sup>}} the difference between true and apparent specific gravities for a substance with specific gravity (20&nbsp;°C/20&nbsp;°C) of about 1.100 would be {{val|0.000120}}. Where the specific gravity of the sample is close to that of water (for example dilute ethanol solutions) the correction is even smaller.
 
===Digital density meters===
;Hydrostatic pressure-based instruments : This technology relies upon Pascal's Principle which states that the pressure difference between two points within a vertical column of fluid is dependent upon the vertical distance between the two points, the density of the fluid and the gravitational force. This technology is often used for tank gauging applications as a convenient means of liquid level and density measure.
 
;Vibrating element transducers : This type of instrument requires a vibrating element to be placed in contact with the fluid of interest. The resonant frequency of the element is measured and is related to the density of the fluid by a characterization that is dependent upon the design of the element. In modern laboratories precise measurements of specific gravity are made using [[oscillating U-tube]] meters. These are capable of measurement to 5 to 6 places beyond the decimal point and are used in the brewing, distilling, pharmaceutical, petroleum and other industries. The instruments measure the actual mass of fluid contained in a fixed volume at temperatures between 0 and 80&nbsp;°C but as they are microprocessor based can calculate apparent or true specific gravity and contain tables relating these to the strengths of common acids, sugar solutions, etc. The vibrating fork immersion probe is another good example of this technology. This technology also includes many coriolis-type mass flow meters which are widely used in chemical and petroleum industry for high accuracy mass flow measurement and can be configured to also output density information based on the resonant frequency of the vibrating flow tubes.
 
;Ultrasonic transducer : Ultrasonic waves are passed from a source, through the fluid of interest, and into a detector which measures the acoustic spectroscopy of the waves. Fluid properties such as density and viscosity can be inferred from the spectrum.
 
;Radiation-based gauge : Radiation is passed from a source, through the fluid of interest, and into a scintillation detector, or counter. As the fluid density increases, the detected radiation "counts" will decrease. The source is typically the radioactive isotope [[cesium-137]], with a half-life of about 30 years. A key advantage for this technology is that the instrument is not required to be in contact with the fluid – typically the source and detector are mounted on the outside of tanks or piping. .<ref>[http://www.ohmartvega.com/en/nuclear_density_DSG.htm Density – VEGA Americas, Inc]. Ohmartvega.com. Retrieved on 2011-11-18.</ref>
 
;Buoyant force transducer : The buoyancy force produced by a float in a homogeneous liquid is equal to the weight of the liquid that is displaced by the float. Since buoyancy force is linear with respect to the density of the liquid within which the float is submerged, the measure of the buoyancy force yields a measure of the density of the liquid. One commercially available unit claims the instrument is capable of measuring specific gravity with an accuracy of ±0.005 SG units. The submersible probe head contains a mathematically characterized spring-float system. When the head is immersed vertically in the liquid, the float moves vertically and the position of the float controls the position of a permanent magnet whose displacement is sensed by a concentric array of Hall-effect linear displacement sensors. The output signals of the sensors are mixed in a dedicated electronics module that provides an output voltage whose magnitude is a direct linear measure of the quantity to be measured.<ref>[http://www.gardco.com/pages/density/electric_hydrometer.cfm Process Control Digital Electronic Hydrometer]. Gardco. Retrieved on 2011-11-18.</ref>
 
;Inline continuous measurement : Slurry is weighed as it travels through the metered section of pipe using a patented, high resolution load cell. This section of pipe is of optimal length such that a truly representative mass of the slurry may be determined. This representative mass is then interrogated by the load cell 110 times per second to ensure accurate and repeatable measurement of the slurry.{{Citation needed|date=July 2013}}
 
==উদাহরণ==
*[[হিলিয়াম]] গ্যাসের ঘনত্ব ০.১৬৪ গ্রাম/লিটার;<ref name="UCSB">[http://web.physics.ucsb.edu/~lecturedemonstrations/Composer/Pages/36.39.html UCSB]</ref> এর ঘনত্ব বাতাসের ০.১৩৯ গুণ।
*[[বাতাসের]] ঘনত্ব ১.১৮ গ্রাম/লিটার। <ref name="UCSB"/>
 
{| class="sortable wikitable"
|+
! উপাদান
! আপেক্ষিক গুরুত্ব
|-----
| [[বালসা কাঠ]] || ০.২
|-----
| [[ওক কাঠ]] || ০.৭৫
|-----
| [[ইথানল]] || ০.৭৮
|-----
| [[জলপাই তেল]] || ০.৯১
|-----
| [[সোডিয়াম]] || ০.৯৭
|-----
| [[পানি]] || ১.০
|-----
| [[ম্যাগনেসিয়াম]] || ১.৪৩
|-----
| [[আয়রন উড]] || ১.৫
|-----
| [[গ্রাফাইট]] || ১.৯-২.৩
|-----
| [[:bn:লবণ|খাবার লবণ]] || ২.১৭
|-----
| [[অ্যালুমিনিয়াম]] || ২.৭
|-----
| [[সিমেন্ট]] || ৩.১৫
|-----
| [[দস্তা]] || ৭.১
|-----
| [[টিন]] || ৭.২৯
|-----
| [[লোহা]] || ৭.৮৭
|-----
| [[নিকেল]] || ৮.২৭
|-----
| [[তামা]] || ৮.৯৬
|-----
| [[বিসমাথ]] || ৯.৮২
|-----
| [[রূপা]] || ১০.৫
|-----
| [[সীসা]] || ১১.৩৫
|-----
| [[পারদ]]|| ১৩.৫৬
|-----
| [[সোনা]]|| ১৯.৩
|-----
| [[ক্ষয়িত ইউরেনিয়াম]] || ১৯.১
|-----
| [[প্লাটিনাম]]|| ২১.৪৫
|-----
| [[অসমিয়াম]] || ২২.৫৯
|}
 
 
*[[:bn:মূত্র|মূত্রের]] স্বাভাবিক আপেক্ষিক গুরুত্ব ১.০০৩ থেকে ১.০৩৫ এর মধ্যে।
*[[:bn:রক্ত|রক্তের]] স্বাভাবিক আপেক্ষিক গুরুত্ব প্রায় ১.০৬০।
*[[ভদকা]] ৮০° প্রুফ (৪০% v/v) এর আপেক্ষিক গুরুত্ব ০.৯৪৯৮।<ref name="Cocktail Specific Gravities">[http://www.goodcocktails.com/bartending/specific_gravity.php Table of liqueurs Specific Gravity]</ref>
 
==আরও দেখুন==
{{div col|colwidth=22em}}
*[[API gravity]]
*[[Baumé scale]]
*[[Buoyancyপ্লবতা]]
*[[Fluid mechanics]]
*[[Gravity (beer)]]
'https://bn.wikipedia.org/wiki/আপেক্ষিক_গুরুত্ব' থেকে আনীত