Saturday, June 27, 2009

Physics in Practice

When biscuits are kept in cool air, they lose their crispness. Then how do they remain crisp when kept in a fridge?

Moisture content in fresh biscuits is about 5% after baking resulting in crisp texture and good storage stability. When they are left open in air they absorb moisture and lose therir crispness. The relative humidity in the atmosphere can vary from 40% during summer to 90% on a cool rainy day. Inside a fridge the temperature is kept low by cooling coils and as well the air is moisture free. As a result the biscuits remain cool as well as crisp. 

What is the difference between air cooler and air conditioner?

Humidity is the moisture or water content of air. An air cooler is basically a humidifier. An air cooler mixes water vapour with air by means of rolling pad of moist cloths of fiber and makes the air the more humid with more moisture content.

An air conditioner or regenerator is a dehumidifier which works as follows: The evaporator in an air conditioner consists of a series of zig-zag copper tubes twinning with thin copper plates. The liquid refrigerant evaporates in the tubes under low pressure so than the tubes and fins get cooled. A fan fixed behind the evaporator drives the warm air that comes through cold fins circulates the cooled air in the room. When the warm air passes through the cold fins the atmospheric moisture condenses on them as drops of water that can be drained away. 

Thursday, June 25, 2009

The operator j in Physics

The operator J in Physics

In a graph all the real numbers can be represented as points on a line positive to the right of the origin and negative to left. For representing the imaginary numbers however we introduce the j factor as an operator. We can convert an imaginary number into a real number by the use of this j operator. For example 1 x j x j = 1 x -1= -1. Thus +1 has been converted into -1 by the operator j which has the value of square root of minus one. The fig.(a) shows that +1 can be converted into -1 by turning the line 01 through 180 degrees. 

 The operation of multiplying +1 by j is equivalent to turning the line 01 through 90 degrees in the anticlockwise direction. 

 The operation of multiplying +1 by j x j is equivalent to turning the line 01 through 180 degrees in the anticlockwise direction.

 The operation of multiplying +1 by j x j x j is equivalent to turning the line 01 through 270 degrees in the anticlockwise direction.

 The operation of multiplying +1 by j x j x j x j is equivalent to turning the line 01 through 360 degrees in the anticlockwise direction.

The operation can also be discussed in the same way for clockwise direction also. Thus we find that all imaginary numbers may be represented graphically by drawing a line through the origin at right angles to the line on which the real numbers are represented. The complex number 4+2j may thus be represented on the diagram by the point A or by the line OA as shown in fig. (b).

Applications of j operator in AC circuits

For an AC circuit containing ohmic resistance, the vector diagram consists of two lines of magnitudes namely voltage E and current I in the same direction. On the Argand diagram they are represented by two distances along the positive axes of real numbers.

For an AC circuit containing only inductance, the applied emf leads the current by 90 degrees and are related to each other by E = wLI. On the Argand diagram the current I is represented along the real positive axis and the voltage E is represented along the positive imaginary axis of the magnitude wLI. The voltage E is therefore fully represented by the equation as E = jwLI.. Thus by including the j operatorin the anticlockwise direction, it very well explains that the voltage E leads current I by 90 degrees.

For an AC circuit containing only capacitance, the applied emf lags the current by 90 degrees and are related to each other by E = I/wL. On the Argand diagram the current I is represented along the real positive axis and the voltage E is represented along the negative imaginary axis of the magnitude I/wL. The voltage E is therefore fully represented by the equation as E = I/jwL.. Thus by including the j operator in the clockwise direction, it very well explains that the current I leads voltage E by 90 degrees.

Monday, June 22, 2009

Thermal Physics and Statistical Mechanics

Name: Thermal Physics & Statistical Mechanics
Authors: Dr.D.Jayaraman and Dr.K.Ilangovan
Publishers: S.Viswanathan (Publishers and Printers) Pvt.Ltd
Old No.38, New No.06, McNicoles Road, Chetpet, Chennai-600031
Phone No. 044-2836 2723/3633
ISBN: 978-81-87156-55-4

Price: Rs.165


1.1. Heat and temperature-1.2 Thermometry-1.2.1 Different of thermometric scales-1.3 Types of thermometers-1.3.1 Calendar’s constant pressure air thermometer-1.3.2 Jolly’s constant volume air thermometer-1.3.3Constant volume hydrogen thermometer-1.3.4 Thermoelectric thermometer-1.3.5 Platinum resistance thermometer-1.4 Thermistor

2.1 Introduction-2.2 Specific heat capacity-2.2.1 Dulong and Petit’s law-2..2.1Confirmation of Dulong and Petit’s law-2.3 Specific heat of solids-2.3.1 Principle of method of mixtures- 2.3.2 Specific heat capacity of solid by the method of mixtures-2.4 Specific heat of liquids-2.4.1 Specific heat capacity of liquid by the method of mixtures-2.4.1 Newton’s law of cooling-2.4.2 Proof of Newton’s law of cooling-2.4.3 Specific heat capacity of liquid by the method of cooling-2.4.4 Specific heat capacity of liquid by Callendar and Barnes’ method-2.5 Radiation correction-2.5.1 Elimination method-2.5.2 Half time correction-2.5.3 Barton’s correction-2.6 Practical application of specific heat capacity-2.7 Specific heat capacity of gases-2.7.1 Mayer’s relation relation between Cp and Cv-2.7.2 Determination of Cv by Joly’s method-2.7.3 Determination of Cp by Ragnault’s method-2.6.4 Determination of Cp by Callendar and Barne’s method

3.1 Introduction-3.2 Melting point-3.2.1 Experiment to determine melting point of wax- 3.2.2 Latent heat of fusion-3.2.3 Laws of fusion-3.2.4 Experiment to determine latent heat of fusion of ice-3.2.5 Practical applications of fusion-3.2.6 Effect of pressure on melting point-3.2.7 Impurities lower freezing point-3.2.8 Supercooling or surfusion-3.3 Vapourisation-3.3.1 Vapour pressure-3.3.2 Experiment to determine vapour pressure of liquid-3.4 Boiling or ebullition-3.4.1 Laws of boiling or ebullition-3.4.2 Latent heat of vapourisation-3.4.3 Latent heat of steam-3.4.4 Experiment to determine the latent heat of steam-3.4.5 Effect of pressure on boiling point-3.4.6 Superheating or delayed boiling-3.5 Evaporation-3.5.1 Cooling due to evaporation-3.6 Atmospheric water vapour and relative humidity-3.6.1 Experiment to determine relative humidity-3.7 Sublimation-3.8 Triple point

4.1 Introduction-4.1.1 Kinetic theory of matter-4.1.2 Three states of matter-4.2 Kinetic theory of gases-4.3 Expression for pressure of gas-4.3.1 Proof of gas laws-4.4 Mean free path-4.5 Maxwell’s velocity distribution law-4.5.1 Average speed-4.5.2 Root mean square-4.5.3 Most probable speed-4.5.4 Ratio of three speeds-4.5.5 Kinetic interpretation of temperature-4.5.6 Brownian movement-4.5.7 Experimental verification of Maxwell’s law-4.5.8 Energy distribution of molecules-4.6 Transport phenomena-4.6.1 Viscosity of gases-Transport of momentum-4.6.2 Thermal conductivity-Transport of thermal energy- 4.6.3 Diffusion-Transport of mass-4.7 Law of equipartition energy-4.7.1 Degrees of freedom-4.7.2 Application to equipartition energy-4.7.3 Variation of specific heat capacity of diatomic gases with temperature

GASES 5.1 Behaviour of real gases-5.2 Andrew’s experiment-5.3 Critical state-5.4 Behaviour of permanent gases-5.4.1 Amagat’s experiment-5.5 Discovery of intermolecular attraction- 5.5.1 Van der Waals’ equation of state-5.5.2 Estimation of critical constants-5.5.3 Validity of Van der Waals equation-5.5.4 Limitations of Van der Waals’ equation

6.1 Introduction-6.2 Production of low temperature-6.3 Production of low temperature-Joule Thomson effect-6.3.1 Joule-Kelvin effect-6.3.2 Temperature inversion-6.4 Liquefaction of gases-6.4.1 Liquefaction of Air-Claude’s method-6.4.2 Liquefaction of Air-Linde’s process-6.4.3 Liquefaction of hydrogen-6.4.4 Liquefaction of helium-6.4.5 Helium I and II and superfluidity-6.5 Adiabatic demagnetization-6.6 Application of low temperatures-6.7 Refrigerating machines-6.7.1 Frigidaire-Vapour compression machine- 6.7.2 Electrolux refrigerator-6.8 Air conditioning machine-6.9 Effects of CFCl2 on ozone layer-6.10 Superconductivity-6.10.1 Introduction-6.10.2 Critical temperature-6.10.3 Isotopic effect-6.10.4 Meissner effect-6.10.5 Type I superconductors-6.10.6 Type II superconductors-6.10.7 Applications of superconductors

7.1 Introduction-7.2 Thermodynamic system-7.3 Thermodynamic equilibrium-Zeroth law of thermodynamics-7.4 Quasistatic process-7.4.1 First law of thermodynamics-7.4.2 Isothermal process-7.4.3 Adiabatic process-7.4.4 Work done in an isothermal process- 7.4.5 Work done in an adiabatic process-7.4.6 Indicator diagram-7.4.7 Relation between adiabatic and isothermal elesticities-7.4.8 Specific heat of a gas at constant volume-U(T,V)-7.4.9 Specific heat of a gas at constant pressure-U(T,P)-7.4.10 Mayer’s relation-7.5 Reversible and irreversible processes-7.5.1 Ideal heat engine-Carnot’s engine- 7.5.2 Carnot’s forward cycle-7.5.3 Carnot’s cycle as refrigerator-7.5.4 Second law of themodynamics-7.5.5 Carnot’s theorem-7.6 Thermodynamic scale of temperature- 7.6.1 Absolute zero on thermodynamic or work scale-7.6.2 Thermodynamic scale and perfect gas scale-7.7 Practical heat engine-7.7.1 Otto engine-7.7.2 Diesel engine-7.7.3 Distinction between Otto and Diesel engines-7.7.4 Heat and work path function-7.8 Entropy-7.8.1 Change in entropy in a reversible process-7.8.2 Change in entropy in a irreversible process-7.8.3 Temperature-entropy diagram-7.8.4 Entropy of a perfect gas in terms of volume and temperature-7.8.5 Entropy of a perfect gas in terms of pressure and temperature-7.8.6 Entropy of a prefect gas in terms of volume and pressure-7.9 Clausius theorem-7.9.1 Clausius inequality-7.9.2 Third law of thermodynamics-7.10 Maxwell’s thermodynamic relations-7.10.1 Applications of thermodynamic relations-7.10.2 Clausius latent heat equation-7.10.3 Claperon latent heat equation

8.1 Introduction-8.2 Conduction-8.2.1 Coefficient of thermal conductivity-8.2.2 Thermal diffusivity-8.2.3 Steady state-8.3 Rectilinear flow of heat along the bar-8.3.1 Thermal conductivity of a good conductor-Forbe’s method-8.4 Thermal conductivity of a bad conductor-8.4.1 Thermal conductivity of a bad conductor-Lee’s disc method

9.1 Introduction-9.2 Radiation-9.3 Black body-9.3.1 Laws of black body radiation- 9.3.2 Fery’s black body-9.3.3 Wien’s black body-9.3.4 Energy distribution in black body radiation-9.3.5 Experimental results-9.3.6 Prevost’s theory of heat exchanges-9.4 Planck’s law-9.5 Wien’s law-9.6 Rayleigh Jean’s law-9.7 Stefan’s law-9.7.1 Experimental verification of Stefan’s law-9.7.2 Experimental determination of Stefan’s law-9.7.3 Newton’s law of cooling deduced from Stefan’s law-9.8 Pyrometery-9.8.1 Total radiation pyrometry-9.8.2 Optical pyrometry-9.8.3 Polarizing optical pyrometer-9.9 Solar energy-9.9.1 Solar constant-9.9.2 Pyroheliometer-9.9.3 Water flow pyroheliometer-9.9.4 Water stir pyroheliometer-9.9.5 Angstrom pyroheliometer-9.9.6 Estimation of true value of solar constant-9.10 Temperature of sun-9.11 Sources of solar energy-9.12 Some everyday applications of solar energy

10.1 Introduction-10.1.1 Principle of statistical mechanics-10.1.2 Phase space-10.1.3 Macro and micro states-10.2 Ensembles and its types-10.2.1 Statistical equilibrium- 10.2.2 Boltzmann’s theorem on entropy and probability-10.2.3 Postulates of statistical mechanics-10.3 Maxwell Boltzmann distribution law (Classical statistics)-0.3.1 Application of Maxwell Boltzmann statistics to an ideal gas-10.4 Quantum statistics- 10.4.1 Postulates of quantum statistics-10.4.2 Bosons and fermions-10.4.3 Distinction between classical particles and quantum particles-10.5 Bose Einstein statistics- 10.5.1 Application of Bose Einstein statistics to Planck radiation law-10.6 Fermi Dirac statistics-10.6.1 Application of Fermi Dirac statistics to Fermi gas-10.6.2 Fermi energy and Fermi temperature-10.7 Comparison between three statistics 

Monday, June 15, 2009

Richard Feynman

Richard Feynman
The famous Tamil writer S.Ramakrishnan in his blog has written the following article about Richard Feynman. With due respect, I acknowledge with thanks for referring the article. Richard Feynman is a theoretical Physicist and I am wondering how a Tamil writer is able to appreciate a Physicist. It should be because of the book about Richard Feynman “Surely you are joking Mr.Feynman” and the short film on the biography of Feynman, “infinity”. If you are interested in Tamil writing, please do visit S.Ramakrishnan’s blog. With kind regards.

ரிச்சர்ட்பெயின்மென அறிவியலில் உயர் ஆய்வு செய்யும் நண்பர் ஒருவரை தற்செயலாகச் சந்தித்தேன். சேர்ந்து காபி குடிக்க சென்றோம். வழியில் பேசிக் கொண்டிருந்த போது ரிச்சர்டு பெயின்மெனை (Richard P. Feynman ) எனக்கு பிடிக்கும். அவரை விரும்பி படித்திருக்கிறேன் என்று சொன்னேன். அவரால் நம்ப முடியவில்லை. வியப்புடன் நீங்கள் பெயின்மெனை எப்படிக் கண்டுபிடித்தீர்கள்.எழுத்தாளர்களுக்கும் விஞ்ஞானத்திற்கும் இடையில் பெரிய இடைவெளி இருக்கிறது என்று தான் நினைத்துக் கொண்டிருந்தேன் என்றார். நானும் அந்த இடைவெளி அப்படியே தானிருக்கிறது. எனக்கும் பெயின்மேனின் இயற்பியல் உயர்தத்துவங்கள் பற்றி எதுவும் தெரியாது. நான் வாசித்திருப்பது அவரது கட்டுரைகளை. அதுவும் சுயசரிதைக் கட்டுரைகளை , குறிப்பாக . Surely You're Joking, Mr. Feynman! What Do You Care What Other People Think? : என்ற புத்தகங்களை பலமுறை வாசித்திருக்கிறேன். மிக அற்புதமான எழுத்து அவருடையது. படிக்க சுவாரஸ்யமும் உள்ளார்ந்த கேலியும் கொண்டிருக்கும். நண்பரின் மானசீக குரு பெயின்மென் தான் என்பது அவர் பேசப்பேச புரிந்தது. அவரே சொன்னார் நான் மட்டுமில்லை.

ஐஐடி மற்றும் ஐஐஎஸ் வட்டாரத்தில் பெயின்மென் மீது ஆதர்சம் கொள்ளாதவர்கள் குறைவு. அவர் ஒரு மேதை , நோபல் பரிசு பெற்ற விஞ்ஞானி என்று புகழ்ந்து கொண்டேயிருந்தார். 1965ம் ஆண்டு இயற்பியலுக்கான நோபல் பரிசு பெற்ற அமெரிக்க விஞ்ஞானி ரிச்சர்ட் பெயின்மென். அமெரிக்காவின் அணுஆய்வு சோதனையில் முக்கிய பங்கு வகித்திருக்கிறார். இயற்பியல் ஆய்வுகள் குறித்து நிறைய உரைகள் நிகழ்த்தியிருக்கிறார். நான் பெயின்மென் பற்றிய எவ்விதமான அறிமுகம் இன்றி அவரது புத்தகங்களை வாசிக்க ஆரம்பித்தேன். அதிலும் குறிப்பாக யூ ஆர் ஜோக்கிங் மிஸ்டர் பெயின்மெனை படித்த போது அவரது இயற்பியல் சாதனைகள் எதையும் அறிந்திருக்கவில்லை. அந்தப் புத்தகம் விஞ்ஞானி ஒருவர் சொந்த வாழ்வில் மேற்கொண்ட சாகசங்கள், சண்டைகள், ஆர்வங்கள் மற்றும் கிறுக்குதனங்கள் பற்றியது. குறிப்பாக பெயின்மெனுக்கு பூட்டை திறப்பது என்றால் ரொம்பவும் பிடிக்கும். எந்த பூட்டையும் அவர் கண்ணில் பார்த்த மாத்திரத்தில் அது என்னவகையான பூட்டு அதை எப்படி திறப்பது என்று யோசிக்க ஆரம்பித்துவிடுவார். எவ்வளவு சிக்கலாக வடிவமைக்கபட்ட பூட்டையும் அவரால் திறந்துவிட முடியும். அப்படியொரு முறை அவர் அமெரிக்க அணுஆய்வு திட்டத்தில் பணியாற்றிய போது அங்கே என்ன நடக்கிறது என்பதை பற்றிய முக்கிய ஆவணங்களை ராணுவ அதிகாரிகள் பாதுகாப்பாக ஒரு பெட்டகத்தில் வைத்து பூட்டி விட்டு சென்றிருந்தார்கள். பெயின்மென் அந்த பூட்டை திறந்து அதிலிந்த தகவல்களை தன் விட்டிற்கு எடுத்துபோய் படிக்க ஆரம்பித்தார். எங்கே அவர்கள் தேடுவார்களோ என்று நினைத்து அதே பாதுகாப்பு பெட்டகத்தில் தனது அடையாள அட்டையை வைத்துவிட்டு வந்துவிட்டார். இதை அவர் விவரிக்கும் அழகிருக்கிறதே அத்தனை நகைக்சுவை.

இது போலவே பெயின்மென் ஒரு மதுவிடுதிக்கு போகிறார். அங்கே துருதுருவென ஏதாவது செய்ய வேண்டும் போலிருக்கிறது. மிதமான போதையை ஏற்றிக் கொண்டு ஒரு மூலையில் அமர்ந்திருந்த ஒரு ஆளின் முன்னால் போய் நின்று அந்த ஆளின் முகத்தில் ஒங்கி ஒரு குத்து குத்திவிட்டு வருகிறார். அந்த ஆள் நிலைகுலைந்து போகிறான். சில நிமிசங்களில் பணியாளர் ஒடி வந்து எதற்காக அந்த ஆளை அடித்தீர்கள் அவன் இப்போது தான் ஜெயிலில் இருந்து விடுதலையாகி வந்திருக்கிறான் என்று சொல்ல பயந்து போன பெயின்மேன் ஏதாவது சொல்லி சமாளி என்று ஒரு ஐம்பது டாலரை அவனிடம் தருகிறார். உடனே பணியாளரும் நீ கதவை நோக்கி நடந்து போகும் போது திரும்பி திரும்பி பார்த்தபடியே போ. மற்றதை நான் பார்த்து கொள்கிறேன் என்கிறான். பெயின்மென் அப்படியே செய்கிறார்அந்த ரௌடியின் அருகில் போய் உன்னை அடித்தவன் இப்போது தான் ஜெயிலில் இருந்து விடுதலையாகி வந்திருக்கிறான். வேறு ஒருவன் என்ற நினைத்து அடித்துவிட்டான் என்று காசை தந்து சமாளிக்கிறான். பெயின்மென் அங்கிருந்து தப்பியோடுகிறார். அதன் பிறகு பல ஆண்டுகாலம் அந்த பார் பக்கம் போகவேயில்லை.இன்னொரு சமயம் பிக்பாக்கெட் அடிப்பது மீது ஆசை அதிகமாகி அதை கற்றுக் கொள்வது என்று முடிவு செய்து பிக்பாக்கெட்காரனிடம் உதவியாளராக சேர்ந்து தொழிலை கற்றுக் கொள்கிறார். பேண்ட் வாசிப்பதில் ஆர்வமாகி ஒருஇசைக்குகுழுவில் சேர்ந்து பேண்ட் வாசிக்கிறார். ஒவியம் கற்றுக்கொள்வதில் ஆர்வம் உண்டாகி தொடர்ந்து பயிற்சி செய்து நவீன ஒவியராகிறார்.

ஒரு நாள் பெண்களை எப்படி வசீகரிப்பது என்று ஒரு மாணவனிடம் கேட்டதும் அவன் மாலையில் பாருக்கு வாருங்கள் கற்று தருகிறேன் என்கிறான். அவரும் போகிறார். அவன் முதலில் இப்படி டிரஸ் பண்ணினால் எந்த பெண்ணும் உங்களை பார்க்கமாட்டாள் என்று அவரது உடையை கலைத்துவிடுகிறான். பிறகு எந்த பொண்ணை பார்த்தாலும் ஹாய் என்று சொல்லுங்கள். அதிலேயே பிக்அப் ஆகிவிடும். இல்லாவிட்டாலும் கையசைத்தபடியே இருங்கள். யாராவது பதிலுக்கு சிரிப்பார்கள். உடனே அருகில் போய் என்னோடு குடிக்க விருப்பமா என்று கேளுங்கள். வந்துவிடுவார்கள். அப்படியே உங்கள் விசிட்டிங்கார்டை தந்து விரும்பும் போது அறைக்கு வரலாம் தனியாக தான் இருக்கிறேன் என்று சொல்லுங்கள் ,பெண்கள் தானே மயங்கிவிடுவார்கள் என்று ஆலோசனை தருகிறான். அது போலவே பாரில் ஒரு பெண்ணை பார்த்து ஹாய் என்கிறார்.அவளும் ஹாய் என்கிறார். உடனே அவர் குடிக்க அழைக்கிறார். விசிட்டிங்கார்டு தருகிறார். அவளும் வருவதாக ஒத்துக் கொள்கிறார். மாணவனுக்கு நன்றி சொல்ல போகையில் அவன் கோபப்பட்டு நீ பழகுவதற்கு என்னுடைய தங்கை தான் கிடைத்தாளா என்று கத்துகிறான். இப்படி அவரது வாழ்வில் உள்ள சுவாரஸ்யங்களை மிக அழகாக எழுதியிருக்கிறார். பொதுவாக விஞ்ஞானிகள் என்றாலே யாரோடும் பேசாதவர்கள். அறிவுஜீவிகள் என்ற தோற்றமிருக்கிறது. குறிப்பாக அவர்களுக்கும் இசை, இலக்கியம், கலை போன்ற துறைகளுக்கும் எந்த தொடர்புமிருக்காது என்றே பிம்பம் உள்ளது.நான் அறிந்தவரை அது பொய்யானது. விஞ்ஞானிகளை போல ஆழமாக இசையை, இலக்கியத்தை ரசித்தவர்களை கலைஉலகில் கூட கண்டதில்லை. ஐன்ஸ்டீன் தீவிரமான புத்தகவாசிப்பு அனுபவம் கொண்டவர். நல்ல இசை ரசிகர். செவ்வியல் இசை குறித்த அவரது கட்டுரைகள் அற்புதமானவை. குறிப்பாக தஸ்தாயெவ்ஸ்கி பற்றிய அவரது பார்வை மிக சிறப்பானது. அவரே குறிப்பிடுவது போல Dostoevsky gives me more than any scientist, more than Gauss." ."

விஞ்ஞானத்தின்முன்னோடி கருத்துகள் இலக்கியத்தில் பதிவாகி உள்ளன. இந்தியாவை சேர்ந்த நோபல் பரிசு பெற்ற விஞ்ஞானியான சுப்ரமணியம் சந்திரசேகர் பீதோவன், நியூட்டன் மற்றும் ஷேக்ஸ்பியர் மூவரையும் ஒப்பிட்டு அவர்களின் படைப்பு ஆளுமையை Truth and Beauty: Aesthetics and Motivations in Science நூலில் விவரிக்கிறார். மிக சுவாரஸ்யமான புத்தகமது.இது போலவே கார்ல் சாகன் என்ற வானவியல் விஞ்ஞானி எழுதிய பிரபஞ்சத்தின் தோற்றம் மற்றும் வானவியல் விஞ்ஞானத்தின் வரலாறு போன்ற புத்தகங்களை வாசித்திருக்கிறேன். அற்புதமான எழுத்து முறை கொண்டவர். இருபதிற்கும் மேலான புத்தகங்களை எழுதியிருக்கிறார். அதில் கான்டாக்ட் என்ற நாவல் குறிப்பிடத்தக்கது. அதை ஹாலிவுட்டில் ராபர்ட் ஜமைக்காஸ் படமாக்கியிருக்கிறார்.தற்போதுள்ள விஞ்ஞானிகளில் ரிச்சர்டு டௌகின்ஸ் என்ற பிரிட்டானிய விலங்கியல் விஞ்ஞானி எழுதிய The Selfish Gene, The Blind Watchmaker, போன்ற புத்தகங்கள் வாசிக்கவும் புரிந்து கொள்ளவும் எளியது. அத்துடன் ஆழமான கருத்துகளையும் நவபார்வையும் கொண்டதாகும்.

மற்றொருவர் உலகப்புகழ்பெற்ற விஞ்ஞானியான ஸ்டீபன் ஹாகின்ஸ். அவர் எழுதிய A Brief History of Time புத்தகம் காலத்தின் சரித்திரத்தை கூறுகிறது. இதை முழுமையாக ஒருவர் புரிந்து கொண்டுவிட்டால் அவர் டாக்டர் பட்டதற்கு சமமாகிவிடுவார் என்கிறார்கள். அவ்வளவு சிக்கலான விஷயத்தை ஹாகின்ஸ் குழந்தைக்கு சொல்வது போல அத்தனை எளிதாக எழுதியிருக்கிறார். அதிலும் விஞ்ஞானிகளின் புத்தகங்களை ஆக்ஸ்போர்ட் கேம்பிரிட்ஜ் போன்ற நிறுவனங்கள் வெளியிடும் போது இவர் ரயில்நிலையங்களில் கூட கிடைக்க கூடிய காமிக்ஸ், மற்றும் ஜனரஞ்சக புத்தகம் வெளியிடும் பாண்டம் பதிப்பகத்தில் தன்னுடைய விஞ்ஞான நூலை வெளியிட்டிருக்கிறார். ஒரு கோடி பிரதிகளுக்கும் மேலாக விற்பனையாகி உள்ளது இந்த புத்தகம். காலம் மற்றும் கருந்துளை குறித்த விரிவான ஆய்விலிருந்து வெளியானதே இந்த நூல். பெயின்மெனின் புத்தகம் அவர் சொல்லி Ralph Leighton எழுதியது. ஐந்து லட்சம் பிரதிகளுக்கும் மேலாக விற்றுள்ள இந்த புத்தகம் பதினாறு மொழிகளில் வெளியாகி உள்ளது. இவை தவிர அவரது முக்கிய புத்தகங்களாக The Pleasure of Finding Things Out , The Feynman Lectures on Physics.. இரண்டையும் குறிப்பிடலாம்.

பெயின்மெனின் மனைவி புற்றுநோயால் மரணமடைந்தார். அதன் பிறகு இரண்டு முறை திருமணம் செய்து கொண்டார். தனது மகள் மற்றும் வளர்ப்பு மகளுடன் ஊர் சுற்றி மனம் விரும்படியாக வாழ்க்கையை செலவிட்டார் . கம்ப்யூட்டரில் ஏற்பட்ட ஆர்வம் காரணமாக அப்பா மகன் இருவரும் கணினி உலகில் நுழைந்து ஆய்வுமேற்கொண்டார்கள். சலிக்காத பயணங்கள் , நடைமுறை வாழ்வில் சாசகம் செய்வது இதுவே அவரது இயல்பு. அவரை டான்குவிகாத்தே என்று நண்பர்கள் கேலி செய்திருக்கிறார்கள்.அவரையும் புற்றுநோய் தாக்கியது. அறுவை சிகிட்சை செய்து கொண்டார். ஆனாலு அவரது உடல்நலம் முழுமையாக தேறவில்லை. 1988 பிப்ரவரியில் இறந்து போனார். பெயின்மேன் வாழ்க்கையை வேடிக்கையான விளையாட்டாகவே எடுத்துக் கொண்டார். விஞ்ஞானத்தை பயமுறுத்தும் விஷயமாக இல்லாமல் மக்கள் வாழ்வோடு கலந்த ஒன்றாகவே கருதினார்.ஒரு நாள் பெயின்மென் நண்பர் ஒருவர் வீட்டில் தேநீர் அருந்தும் போது அவரது மனைவி தேநீரில் பால் கலக்கவா அல்லது எலுமிச்சைபழமா என்று கேட்டார். ஏதோ யோசனையில் இரண்டும் என்று பெயின்மேன் பதில் சொல்லியிருக்கிறார். பாலில் எலுமிச்சை கலந்தால் திரிந்து போய்விடும் என்பதை மறந்து அவர் சொன்னதை கேட்டு வியப்படைந்த பெண் சொன்னது தான் Surely You're Joking, Mr. Feynman! . அதுவே அவரது புத்தகத்தின் தலைப்பாகியது. ஒரு முறை அவர் வழக்கமாக குடிக்கும் பார் இரவில் நெடுநேரம் திறந்து வைக்கபட்டிருக்கிறது. அங்கே சட்டஒழுங்கு பராமரிக்கபடவில்லை என்று மூடுவதற்கு கோர்ட் ஆணையிட்டது. கோர்டில் ஒரு குடிகாரன் என்ற முறையில் பெயின்மென் ஆஜராகி மதுவிடுதிகள் எளிய மக்களின் சந்திப்பு வெளி. அங்கே பேராசிரியர், லோக்கல் ஆள், படித்தவன் படிக்காதவன் அனைவரும் சமம். குடிப்பவர்கள் ஒருவர் சந்தோஷத்தை மற்றவருக்கு பகிர்ந்து தருகிறார்கள். ஆகவே அதை தடை செய்ய கூடாது. குடிப்பதற்கு நேரம் காலம் எதற்கு என்று வாதாடினார். முடிவில் அந்த கேஸ் வெற்றி பெற்று பார் மீண்டும் திறக்கபட்டதுஇப்படி பெயின்மேன் என்ற விஞ்ஞானி தான் நோபல் பரிசு பெற்றவன். மற்றவர்களை விட பெரிய புத்திசாலி என்பதை தூக்கி வைத்துவிட்டு வாழ்க்கையை கொண்டாடியிருக்கிறார். இதற்காகவே அவரை தேடித்தேடி வாசிக்கிறேன் என்று சொன்னேன்.

விடைபெறும் போது நண்பர் ரிச்சர்டு பெயின்மேன் வாழ்வினை பற்றி Infinity என்றொரு படம் வந்திருக்கிறது. அனுப்பி வைக்கிறேன். பாருங்கள் என்று சொல்லி போனார். பெயின்மேனின் படத்தை காண்பதற்காக காத்துக் கொண்டிருக்கிறேன். இன்னொரு முறை பெயின்மேன் புத்தகத்தையும் படிக்க ஆர்வமாக இருந்தது. புத்தக குவியல்களுக்குள் எங்கேயிருக்கிறது என்று தேட வேண்டும். தேடும்போது தான் அதை யார் எடுத்து போயிருக்கிறார்கள். எங்கே என்ற விபரங்கள் நினைவிற்கு வரும் . உலகில் மிக சிரமமானது புத்தகங்களை காப்பாற்றி வைப்பது தான். ஆனாலும் புத்தகத்தின் விதியே அது இடம்மாறி போய்க்கொண்டேயிருப்பது தானே.

Sunday, June 14, 2009

Ralph de Laer Kronig

Ralph Kronig

Ralph Kronig was a German-American physicist (1904-1995). He is noted for the discovery of particle spin and for his theory of x-ray absorption spectroscopy. His theories include the Kronig-Penney model for allowed and forbidden bands in solids Ralph Kronig (later Ralph de Laer Kronig) was born in 1904 from American parents in Dresden, Germany where he received his primary education. He went to New York to study at Columbia University until 1925 where he was an assistant professor.

In 1925, when Kronig was a young Columbia University PhD who had spent two years studying in Europe, he first proposed electron "spin" in Copenhagen. Werner Heisenberg and Wolfgang Pauli immediately hated the idea. They had just ruled out all imaginable actions from quantum mechanics. Now Kronig was proposing to set the electron rotating in space. Pauli especially ridiculed the idea of spin, saying that "it is indeed very clever but of course has nothing to do with reality". Faced with such criticism, Kronig decided not to publish his theory and the idea of electron spin had to wait for others to take the credit. Ralph Kronig, had come up with the idea of electron spin several months before Uhlenbeck and Goudsmit, however, most textbooks credit these two men with the discovery.

Ralph Kronig did not hold a grudge against Pauli for this turn of events. In fact, Kronig and Pauli remained friends for many years into the future. They exchanged many ideas in physics through letters. However, many have argued (especially Dutch physicists) that Pauli only received the Nobel Prize for his exclusion principle due to Kronig's theory of particle spin. The argument stems from the fact that Kronig had told Pauli about electron spin before Pauli had published his paper showing that two electrons can inhabit the same orbital (W. Pauli, “On the Connexion between the Completion of Electron Groups in an Atom with the Complex Structure of Spectra”, Z. Physik 31, 765ff, 1925). Months later when Uhlenbeck and Goudsmit came up with particle spin, it seemed to verify Pauli's paper.

In 1927, Kronig returned to Europe and remained there working in different prominent centres of research: Copenhagen, London, Zürich (where for a year he was Pauli's assistant). Around 1930 he settled in the Netherlands: first in Utrecht, afterwards in Groningen. Kronig and Penney (1931) published a one dimensional model of a crystal that showed how the electrons in a crystal would be dispersed into allowed and forbidden bands by scattering from the extended linear array of atoms. Kronig was later in 1939 to be appointed a professor of theoretical physics in the Netherlands and to devote his life to research. The Max Planck medal was awarded to Ralph Kronig in 1962.

Atomic Theory


Science and philosophy were both highly developed disciplines in ancient India. However, Indian philosophic thought was considerably more mature and traditionally we misunderstand that any early scientific contributions came only from the west, particularly from Greece. Because of this erroneous belief, which is perpetuated by a wide variety of scholars, it is necessary to briefly examine the history of Indian scientific thought. Grant Duff British Historian of India said that many of the advances in the sciences that we consider today to have been made in Europe were in fact made in India centuries ago. It is true that India has given us extraordinary gifts like grammar and logic, philosophy and fables, hypnotism and chess, and above all numerals and decimal system.

To their credit the Indians have made great strides in the study of numbers and of geometry. They have acquired immense information and reached the zenith in their knowledge of the movements of the stars (astronomy). Sir William Wilson Hunter author of the book, “The Indian Empire”, said that India has even contributed to modern medical science by the discovery of various chemicals and by teaching you how to reform misshapen ears and noses. Ancient Indians measured the land, divided the year, mapped out the heavens, traced the course of the sun and the planets through the zodiacal belt, analyzed the constitution of matter, and studied the nature of birds and beasts, plants and seeds. India's contribution to the sciences of mathematics and medicine has been unique. In other sciences, especially linguistics, metallurgy, and chemistry, Indians made trail-blazing discoveries. India has a much more realistic view of the matter. It says

“Who knows for certain? Who shall here declare it?
Whence was it born, whence came creation?
The gods are later than this world’s formation;
Who then can know the origins of the world?
None knows whence creation arose;
And whether he has or has not made it;
He who surveys it from the lofty skies,
Only he knows- or perhaps he knows not”.

It is understood that the Indian philosophy has contributed some scientific facts, but it is to be evaluated on what capacity these scientific points are still valid in this era of high technology. So in this paper we are going to have a comparative study of atomic theory on the basis of physics and philosophy.

Vaishesika theory of atomism
India developed very early, enduring atomist theories of matter. Possibly, Greek atomistic thought was influenced by India, via the Persian civilization. Kanaada, the founder of the Vaishesika system of philosophy, expounded that the entire matter in this world consists of atoms as many in kind as the various elements. Kanaada said that the cause of creative motion is believed to be adrsta, unseen moral force which guides the destiny of souls according to their karma and requires them to be provided with properly equipped bodies and an appropriate objective world for the experience of pleasure and pain. It is due to the operation of this metempirical force that atoms start moving to get together in order that they may be integrated into countless varieties of things. Although the Vaishesika system developed independently from the Nyaya, the two eventually merged because of their closely related metaphysical theories. In its classical form, however, the Vaishesika school differed from the Nyaya in one crucial respect: where Nyaya accepted four sources of valid knowledge, the Vaishesika accepted only perception and inference. Vaishesika atomism also differs from the atomic theory of modern science: according to the Vaishesikas, the functioning of atoms was guided or directed by the will of the Supreme Being. This is therefore a theistic form of atomism. Kanaada was an expounder of the law of causation and of the atomic theory. He classified all the objects of creation into nine elements, namely: earth, water, light, wind, ether, time, space, mind and soul. According to his theory every object of creation is made of atoms, which in turn are joined with each other to form molecules.

This statement is very similar to the John Dalton’s atomic theory proposed after 2500 years. Kanaada has also described the dimension and motion of atoms and their chemical reactions with each other. In Vaiseshika philosophy, Kanaada (600 B. C) claimed that elements could not be destroyed. Kanaada's theory stated that basic particles mix together as the building blocks for all matter. It is true that the atomic theories of ancient India are brilliant imaginative explanations of the physical structure of the world. Some Jain thinkers went a step further. They thought that all atoms are the same kind and variety emerged because they entered into different combinations. Kanaada thought that light and heat are variations of the same reality. Umasvati, who lived in the first century A.D., suggested that atoms of opposite qualities alone combined and the atoms attracted or repelled, as they were heterogeneous or homogenous.

John Dalton's Atomic theory
In 1804 Dalton, put forward his atomic theory according to which all matter was composed of very small particles called atoms. All atoms of a given element are identical. The atoms of a given element are different than those of any other element. Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers of types of atoms. Atoms are indivisible in chemical processes. Atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way atoms are grouped together.

Prout’s atomic theory
Prout, a contemporary of Dalton proposed that all the substances were made of hydrogen atoms because the study of the atomic weights of the various substances seemed to indicate that they were simple multiples of the atomic weight of hydrogen. The atomic view of matter was further supported by the successful development of the kinetic theory of gases which is based on the assumption that the atoms of a gas act as elastic and impenetrable solid spheres, exerting no force upon one another except at the time of collision. This theory leads to the correct interpretation of heat and temperature and is able to derive all the gas laws on the above assumptions.

J.J.Thomson atom model
After Eugen Goldstein’s 1886 discovery that atoms had positive charges, J.J.Thomson proposed in 1898 an atom model that the atom was supposed to be sphere filled with positively charged matter of uniform density in which just sufficient numbers of electrons were embedded to balance the positive charge. Since the electrons placed within the positive charge resembled the plums in a pudding the atom model is some times referred to as plum pudding model. The electrons were further supposed to possess vibratory motion about their equilibrium position so as to account for the emission of light. When no light was being emitted the electrons were supposed to be at rest.

Rutherford atom model
In 1908, Ernest Rutherford, a former student of Thomson's, proved Thomson's plum pudding structure incorrect. Rutherford and his two associates Geiger and Marsden performed a series of experiments with radioactive alpha particles. Rutherford fired tiny alpha particles made up of positively charge particles, at solid objects such as gold foil. He found that while most of the alpha particles passed right through the gold foil, a small number of alpha particles passed through at an angle, and some bounced straight back like a tennis ball hitting a wall. Rutherford's experiments suggested that gold foil, and matter in general, had holes in it! These holes allowed most of the alpha particles to pass directly through, while a small number ricocheted off or bounced straight back because they hit a solid object.

In 1911, Rutherford proposed a revolutionary view of the atom. He suggested that the atom consisted of a small, dense core of positively charged particles in the center (or nucleus) of the atom, surrounded by a swirling ring of electrons. The nucleus was so dense that the alpha particles would bounce off of it, but the electrons were so tiny, and spread out at such great distances that the alpha particles would pass right through this area of the atom. Rutherford's atom resembled a tiny solar system with the positively charged nucleus always at the center and the electrons revolving around the nucleus. The positively charged particles in the nucleus of the atom were called protons. Protons carry an equal, but opposite, charge to electrons, but protons are much larger and heavier than electrons. In 1932, James Chadwick discovered a third type of sub-atomic particle that he named the neutron. Neutrons help stabilize the protons in the atom's nucleus. Because the nucleus is so tightly packed together, the positively charged protons would tend to repel each other normally. Neutrons help to reduce the repulsion between protons and stabilize the atom's nucleus. Neutrons always reside in the nucleus of atoms and they are about the same size as protons. However, neutrons do not have any electrical charge, they are electrically neutral. Atoms are electrically neutral because the number of protons (+ charges) is equal to the number of electrons (- charges) and thus the two cancel out. As the atom gets larger, the number of protons increases, and so does the number of electrons (in the neutral state of the atom).

Atoms are extremely small. One hydrogen atom (the smallest atom known) is approximately 5 x 10-8 mm in diameter. Atoms of different elements are distinguished from each other by their number of protons (the number of protons is constant for all atoms of a single element, the number of neutrons and electrons can vary under some circumstances). To identify this important characteristic of atoms, the term atomic number (z) is used to describe the number of protons in an atom. For example, z = 1 for hydrogen and z = 2 for helium. Another important characteristic of an atom is its weight, or atomic mass. The total number of protons and neutrons in the atom roughly determines the weight of an atom. While protons and neutrons are about the same size, the electron is more that 1,800 times smaller than the two. Thus the electrons' weight is inconsequential in determining the weight of an atom: it's like comparing the weight of a flea to the weight of an elephant.

Niels Bohr atom model
Ernest Rutherford's view of the atom consisted of a dense nucleus surrounded by freely spinning electrons. In 1913, the Danish physicist Niels Bohr proposed yet another modification to the theory of atomic structure based on a curious phenomenon called line spectra. Bohr hypothesized that electrons occupy specific energy levels. When an atom is excited, such as during heating, electrons can jump to higher levels. When the electrons fall back to lower energy levels, precise quanta of energy are released as specific wavelengths (lines) of light.

Under Bohr's theory, an electron's energy levels, also called as electron shells can be imagined as concentric circles around the nucleus. Normally, electrons exist in the ground state, meaning they occupy the lowest energy level possible, the electron shell closest to the nucleus. When an electron is excited by adding energy to an atom (for example, when it is heated), the electron will absorb energy, 'jump' to a higher energy level and spin in the higher energy level.

After a short time, this electron will spontaneously 'fall' back to a lower energy level, giving off a quantum of light energy. Bohr not only predicted that electrons would occupy specific energy levels; he also predicted that those levels had limits to the number of electrons each could hold. Under Bohr's theory, the maximum capacity of the first (or innermost) electron shell is two electrons. For any element with more than two electrons, the extra electrons will reside in additional electron shells. For example, in the ground state configuration of lithium (which has three electrons) two electrons occupy the first shell and one electron occupies the second shell.

Commenting on the theories of atomism in philosophy, L Basham remarks that Indian atomic theories were not of course, based on experiment, but on intuition and logic. Vaishesika theory of atomism says that every object of creation is made of atoms and when they are joined with each other to form molecules. Kanaada has also described the dimension and motion of atoms and their chemical reactions with each other. In Vaishesika philosophy, Kanaada (600 B. C) claimed that elements could not be destroyed. Kanaada's theory stated that basic particles mix together as the building blocks for all matter. These statements are very similar to the John Dalton’s atomic theory. But Vaishesika atomism differs from the atomic theory of modern science: according to the Vaishesikas, the functioning of atoms was guided or directed by the will of the Supreme Being. This is therefore a theistic form of atomism. In Physics there is no question of theism and only experiments are giving way to many theories of atom. Dalton’s theory, Prout’s theory, Thomson’s theory, Ruther ford’s theory, Bohr’s theory, Sommerfeld’s theory, Vector atom model, Liquid drop model and shell model are all based on experimental evidences. Though Vaishesika theory of atomism in philosophy has been predicated based on some logic, it has given an idea about an atom before 2500 years. The atomic theories developed in physics within 200 years based on experiments lead to scientific developments namely nuclear fission, nuclear fusion, artificial transmutation of elements namely artificial radio-isotopes, atom bomb, hydrogen bomb, nuclear energy nuclear power, nuclear medicine and many more. Hence, at least we can accept the statement given by Grant Duff British Historian of India that many of the advances in the sciences that we consider today to have been made in Europe were in fact made in India centuries ago.

Chidambara Kulkarni, Indian History and Culture, Orient Longman Ltd. 1974. (268).
D.P.Singhal, India and World Civilization, Macmillan India Ltd, 1993 (153 - 188).
S.Natarajan, Indian Culture, Indo-Middle East Cultural Studies Hyderabad, 1960, (68).
Jawaharlal Nehru, The Discovery of India, Oxford University Press. 1995(216).
Swami Tattwananda, Ancient Indian Culture At A Glance, Oxford Book Co. 1962 (127).
K.Ilangovan, Engineering Physics, Anuradha Agencies, Kumbakonam (1987).
Jadunath sinha, Indian Philosophy, New Central book agency, Kolkata.

Interesting Questions in Physics


The racing cars are driven only on dry tracks because
a) they can run faster only on dry tracks.
b) they may not skid in dry tracks.
c) the racing car tyres are not grooved.
d) the racing cars tyres are having wide base.

Answer: c
Explanation: Ordinary car tyres have grooves at their bottom so that it will not skid on wet roads and since the racing car tyres are not grooved it has to be driven only on dry roads

Out of the following, the one that is not a unit of length
a) angstrom.
b) micron.
c) parsec.
d) radian.

Answer: d
Explanation: Parsec is the unit of length used in astronomy 1 parsec=3.2616 light year

The equation E = mc2 gives the amount of energy released as a result of nuclear fission. What does the term 'm' stands for
a) the original mass of the nuclei
b) the final total mass of the nuclei
c) the increase in total mass of the nuclei
d) the decrease in total mass of the nuclei

Answer: d
Explanation: It is a good question. Many of them think that the term ‘m’ in the equation as the total mass. But actually, during fission reaction, there is a decrease in mass and this decrease in mass is referred as m in that equation. In fact this decrease in mass is released as energy in the fission reaction.

A ballet dancer can increase her angular velocity by folding her arms as this
a) increases the moment of inertia.
b) decreases the moment of inertia.
c) makes the MI to be zero.
d) makes the MI to be constant.

Answer: b
Explanation: The angular velocity is inversely proportional to the moment of inertia and hence Iw = constant.

A block of ice in a room at normal temperature.
a) does not radiate.
b) radiates less but absorbs more.
c) radiates more than it absorbs.
d) radiates as much as it absorbs.

Answer: b
Explanation: Ice is at a temperature of 0 C and so it radiates less. Since the room temperature is very much more than the temperature of ice it absorbs more.

The number of images of an object held between the parallel plane mirrors.
a) infinity.
b) one.
c) three.
d) Zero

Answer: a
Explanation: The formula for number of images formed when two mirrors are fixed with an angle = [(360/angle between the mirrors) –1], In this case the mirrors are kept with an angle of zero and so the number of images formed = [(360/0) –1] = infinity

Two lenses of power +12 and –2 dioptres are placed in contact. The focal length of the combination is.
a) 7.14 cm.
b) 10 cm
c) 12 cm
d) 14 cm

Answer: b
Explanation: The total power of the combination = 12-2 = 10. The power = reciprocal of focal length. Focal length = 1/10 metre = 10 cm

A converging lens is used to form an image on the screen. When the lower half of the lens is covered by an opaque screen then.
a) half of the image will disappear.
b) Complete image will be formed
c) No image is formed
d) Intensity of the image is high.

Answer: b
Explanation: The image formation not based on the size of the lens, but it is based on where the object is kept.

A man of 1.80 metre tall standing in front of a plane mirror. What is the minimum size of the mirror required to see his complete image.
a) 0.90 metre.
b) 1.80 metre
c) 0.45 metre
d) 1 metre

Answer: a
Explanation: Based on the laws of reflection, it has been calculated that the minimum size of the mirror required to view the full size of man is half of his height.

Which one of the following statement is not a feature of dry cell.
a) small size and easily portable
b) chemical reactions and irreversible
c) internal resistance is small
d) easily rechargeable

Answer: d
Explanation: The only disadvantage of the dry cell is that it cannot be recharged like a secondary batter or alkaline battery.

Nichrome which is used as heating element it has
a) low specific heat
b) low melting point
c) high specific heat
d) high conductivity

Answer: c
Explanation: Nichrome is an alloy; combination of metals of nickel and chromium and Nichrome will not get oxidized so easily, it has high melting point and high specific heat capacity.

Of the following devices which has small resistance
a) moving coil galvanometer
b) ammeter of range 0-1 A
c) ammeter of range 0-10 A
d) voltmeter

Answer: c
Explanation: The instrument which has a very small resistance can only measure a large current and in that principle, the ammeter which can measure a maximum current of 10 A must have a small resistance

Electromagnetic induction is not used in
a) transformer
b) room heater
c) ac generator
d) choke coil

Answer: b
Explanation: The room heater is operated on the principle of electrical energy is converted into heating energy by a coil of wire made of nichrome.

Transformer works on
a) ac only
b) dc only
c) both ac and dc
d) ac more effective than dc

Answer: a
Explanation: A transformer works on the principle of mutual induction and hence it can operate only on ac. It is a suitable example for the static induction.

Which of the following cannot be stepped up in transformer
a) input current
b) input voltage
c) input power
d) all the above

Answer: c
Explanation: The input power cannot be stepped up in the transformer. In transformer input power is equal to the output power.

Radio carbon dating is done by estimating in the specimen
a) the amount of ordinary carbon still present
b) the amount of radio carbon still present
c) the ratio of amount of radio and ordinary carbon still present
d) the ratio of amount of ordinary and radio carbon still present

Answer: c
Explanation: Radio carbon dating is used to determine age of fossils, which will stop absorbing radiocarbon once they are dead. So the age of fossils can be determined based on the ratio of amount of ordinary and radiocarbon present in them.

The rate of cooling of two different liquids in exactly similar calorimeters and kept in identical surroundings are the same if
a) the masses of the liquids are the same
b) equal masses of the liquids at the same temperature are taken
c) different volumes of the liquids at the same temperature are taken
d) equal volumes of the liquids at the same temperature are taken

Answer: d
Explanation: Newton’s law of cooling states that the rate of cooling of two different liquids put in exactly similar calorimeters and kept in identical surroundings are the same if equal volumes of the liquid at the same temperature are taken.

Which are the following statement is not true about thermal radiation
a) all bodies emit thermal radiation at all temperature
b) thermal radiation are electromagnetic waves
c) thermal radiations are not reflected from mirror
d) thermal radiations travel in free space with velocity of 3x108 m/s

Answer: c
Explanation: Thermal radiations have the properties of light and so it can be reflected from mirror.

A hollow metallic sphere filled with water is hung from a support by a long thread a small hole is made at the bottom of the sphere and it is oscillated. how will the time period of oscillations be affected as water slowly flows out of the hole
a) the time period will remain unchanged as water is flowing out.
b) The time period will keep increasing until the sphere is empty
c) The time period will keep decreasing until the sphere is empty.
d) The time period will increase at first then decrease until the sphere is empty. Initially the period will be the same as that when the sphere was full of water

Answer: d
Explanation: The length of the pendulum is the distance between the point of support and the center of gravity of the sphere. The center of gravity of the sphere is at the center when it is empty and completely filled with water. The center gravity falls below the center of the sphere as the water flows out until the sphere is half full and after which the center of gravity begins to raise, hence the effective length of the pendulum. Hence its time period will increase at first and decrease until the sphere is empty when it becomes equal to the time period when the sphere was full of water.

Which of the following is connected to a galvanometer to convert galvanometer as an ammeter
a) a low resistance in series
b) a high resistance in series
c) a high resistance in parallel
d) a low resistance in parallel

Answer: d
Explanation: If a galvanometer to be converted into an ammeter it has to be connected with a low resistance in parallel and if the galvanometer to be converted into a voltmeter it has to be connected with a high resistance in series.

A bird sitting on an uninsulated wire carrying a current feels quite safe because
a) the bird is a non conductor of electricity
b) resistance of the bird is very large
c) there is a large potential difference between the bird and wire
d) there is no potential difference between the bird and the wire

Answer: d
Explanation: Since the bird is sitting on the live wire, there is no potential difference maintained between the bird and the live wire. Suppose a person catches the live wire by standing on earth, there is potential difference between the live wire and the earth (earth is zero potential) and so current passes through the person.

The process responsible for the beautiful colours produced when white light is incident on a thin soap film is
a) scattering of light
b) interference of light
c) dispersion of light
d) refraction of light

Answer: b
Explanation: When light passes through the soap film, there shall be two light rays, which are coherent, but they have a phase difference and they form an interference pattern

Which of the following statement is wrong
a) visible region lies between ir and uv region
b) the sensitivity of eye is maximum for light of wavelength 600 nm
c) microwaves used in radar
d) X rays are used in the study of crystal structure

Answer: b
Explanation: The sensitivity of eye is highest for light of wavelength 560 nm, which is green colour.

When you stand in base feet with one foot on the stone floor and the other on a carpet .The stone floor foot feels colder than the carpet, what is the most likely explanation
a) the stone floor is at a lower temperature than carpet
b) air is unable to circulate through the carpet fibers
c) more energy flows from your foot to stone floor than from the foot with the carpet
d) more energy flows from your foot to carpet floor than from the foot with stone

Answer: c
Explanation: Stone is a good conductor of heat and conducts heat away and foot feels colder on the stone floor. Carpet is bad conductor of heat and does not conduct heat and the foot feels warmer.

An unlit match is held near to an extremely hot Bunsen flame, the match does not get hot enough to light because
e) the flame is not hot enough
f) the flame does not radiate any heat sideways
g) a match can only be lit striking it on a rough surface
h) air is a bad conductor of heat

Answer: d
Explanation: Air being bad conductor does not help the heat to travel to the match to heat up.

A spanner is used to loosen a nut. The turning effects depend on the force applied and the perpendicular distance from the force to the nut. What name given to the turning effect
i) moment
j) couple
k) torque
l) pressure

Answer: a
Explanation: The turning effect of a force is called a moment. That is why the moment of a momentum is called angular momentum.

A sound wave from violin has a larger amplitude than that from a flute. The sound wave from the flute has a higher frequency than that from the violin. Which instrument produces louder sound and which produces the sound of higher pitch.
m) flute and flute
n) flute and violin
o) violin and flute
p) violin and violin

Answer: c
Explanation: The amplitude is related to the loudness and the frequency is related to the pitch of a sound

Many houses have electricity meter that is read so that the cost of electricity used by the customer may be calculated. What does the electricity meter record?
q) voltage
r) current
s) power
t) energy

Answer: b
Explanation: The meter in our houses measures the electrical energy in terms of units. I unit =1000 Watt of electrical energy

In a cream separator the heavier particles of skimmed milk move away from the center and move towards the wall of the container. This is because of
u) Centripetal force.
v) Centrifugal force
w) Surface tension
x) viscosity

Answer: b
Explanation: The centrifuge machine consists of a vessel rotated with a high speed by using an electrical motor. When the vessel is filled with liquid, the particles experience the centrifugal force and try to fly away from the center. The centrifugal force is mrw2 and as w is the same for all the particles, centrifugal force is greater

On what does the quality of a sound wave depend
y) the loudness of the sound
z) the pitch of the sound
aa) the shape of the sound
bb) the speed of the sound

Answer: c
The shape of the sound wave decides the quality of the sound.

Thursday, June 11, 2009

Surface Tension

Surface Tension
The cohesive forces between liquid molecules are responsible for the phenomenon known as surface tension. The molecules at the surface do not have other like molecules on all sides of them and consequently they cohere more strongly to those directly associated with them on the surface. This forms a surface "film" which makes it more difficult to move an object through the surface than to move it when it is completely submersed. Surface tension is typically measured in dynes/cm, the force in dynes required to break a film of length 1 cm. Equivalently, it can be stated as surface energy in ergs per square centimeter. Water at 20°C has a surface tension of 72.8 dynes/cm compared to 22.3 for ethyl alcohol and 465 for mercury. Decrease in water surface tension with heating

Cohesion and Surface Tension
The cohesive forces between molecules down into a liquid are shared with all neighboring atoms. Those on the surface have no neighboring atoms above, and exhibit stronger attractive forces upon their nearest neighbors on the surface. This enhancement of the intermolecular attractive forces at the surface is called surface tension.

Surface Tension of Water
The surface tension of water is 72 dynes/cm at 25°C . It would take a force of 72 dynes to break a surface film of water 1 cm long. The surface tension of water decreases significantly with temperature as shown in the graph. The surface tension arises from the polar nature of the water molecule. Hot water is a better cleaning agent because the lower surface tension makes it a better "wetting agent" to get into pores and fissures rather than bridging them with surface tension. Soaps and detergents further lower the surface tension.

Cohesion and Adhesion
Molecules liquid state experience strong intermolecular attractive forces. When those forces are between like molecules, they are referred to as cohesive forces. For example, the molecules of a water droplet are held together by cohesive forces, and the especially strong cohesive forces at the surface constitute surface tension.When the attractive forces are between unlike molecules, they are said to be adhesive forces. The adhesive forces between water molecules and the walls of a glass tube are stronger than the cohesive forces lead to an upward turning meniscus at the walls of the vessel and contribute to capillary action.The attractive forces between molecules in a liquid can be viewed as residual electrostatic forces and are sometimes called van der Waals forces or van der Waals bonds.

Surface Tension in our life
Walking on water
Small insects such as the water strider can walk on water because their weight is not enough to penetrate the surface.

Floating a needle
If carefully placed on the surface, a small needle can be made to float on the surface of water even though it is several times as dense as water. If the surface is agitated to break up the surface tension, then needle will quickly sink.

Don't touch the tent!
Common tent materials are somewhat rainproof in that the surface tension of water will bridge the pores in the finely woven material. But if you touch the tent material with your finger, you break the surface tension and the rain will drip through.

Soaps and detergents
help the cleaning of clothes by lowering the surface tension of the water so that it more readily soaks into pores and soiled areas.

Clinical test for jaundice
Normal urine has a surface tension of about 66 dynes/cm but if bile is present (a test for jaundice), it drops to about 55. In the Hay test, powdered sulfur is sprinkled on the urine surface. It will float on normal urine, but sink if the S.T. is lowered by the bile.

Washing with cold water
The major reason for using hot water for washing is that its surface tension is lower and it is a better wetting agent. But if the detergent lowers the surface tension, the heating may be unnecessary.

Surface tension disinfectants
Disinfectants are usually solutions of low surface tension. This allows them to spread out on the cell walls of bacteria and disrupt them. One such disinfectant, S.T.37, has a name which points to its low surface tension compared to the 72 dynes/cm for water.

Tuesday, June 9, 2009

Solid State Physics

Name : Solid State Physics

Authors : K.Ilangovan

Price : Rs. 160/-

No. of Pages : 296

ISBN : 81-87156-24-4

Publishers : S. Viswanathan(Printers & Publishers), Chennai - 31
Chapter Details

1. Crystal Structure,1.1. Introduction, 1.2. Basic Concepts of Crystallography, 1.3. Bravais Lattice, 1.4. Crystal Planes and Miller Indices, 1.5. Crystal Structures, 1.6. Important Crystal Structures, Review Questions,

CHAPTER 2. Diffraction of X–Rays by Crystals, 2.1. Introduction, 2.2. Bragg’s Law, 2.3. Experimental Methods In X-ray Diffraction,

CHAPTER 3. Chemical Bonds, 3.1. Review of Atomic Structure, 3.2. Primary Bonds, 3.3. Secondary Bonds, 3.4. Bond Energy Review Questions,

CHAPTER 4 Deffects in Solids, 4.1. Introduction, 4.2. Crystal Imperfections, 4.3. Effects of Crystal Imperfections Review Questions,

CHAPTER 5. Specific Heat Capacity of Solids, 5.1. Lattice Vibrations, 5.2. Phonons of Monoatomic one Dimenstional Lattice, 5.3. Basic Definitions, 5.4. Dulong and Petit’s Law, 5.5. Einstein’s Theory of Specific Heat, 5.6. Debye’s Theory of Specific Heat Review Questions,

CHAPTER 6. Magnetic Materials , 6.1. Introduction, 6.2. Basic Definitions, 6.3. Classifications of Magnetic Materials, 6.4. Diamagnetic Materials, 6.5. Paramagnetic Materials, 6.6. Ferromagnetic Materials, 6.7. Antiferromagnetic Materials, 6.8.Ferrimagnetic Materials, 6.9. Hard Magnetic Materials, 6.10. Soft Magnetic Materials,

CHAPTER 7. Superconductivity : 7.1. Introduction, 7.2. Properties of Superconductors, 7.3. Types of Superconductors, 7.4. BCS Theory ofSuperconductivity, 7.5. London Equations,Josepson Effect, 7.7. Superconducting Materials, 7.8. Characteristic Properties of Superconductors,

CHAPTER 8. Dielectric Materials, 8.1. Introduction, 8.2. Basic Definitions, 8.3. Electric Polarization and Different Types of Polarizations, 8.4. Dielectric Loss, 8.5. Local Field or Internal Field, Determination of Dielectric Constant, Dielectric Brekdown, 8.8. Properties of Dielectric Materials, 8.9. Classification of Insulating Materials, 8.10. Applications of insulating materials, 8.11. Ferroelectric Materials, 8.12.Piezoelectric and Pyroelectric Materials,

CHAPTER 9. Semiconductors, 9.1.Introduction, 9.2. Intrinsic Semiconductors, Extrinsic Semiconductors, 9.4. Variation of Carrier Concentration With Temperature, Hall Effect-determination of Hall Coefficient Review Questions,

CHAPTER 10. Conductors : Introduction, 10.2. The Classical Free Electron Theory (drude Lorentz Theory), 10.3. Quantum Free Electron Theory, 10.4. Band Theory of Solids, 10.5. Classifications of Solids,10.6. Different Types of Conducting Materials.