How does mass depend on speed?


In order to answer this question, we have to consider two situations:

a) The object could be at rest in our reference frame.

b) The "object" is never at rest in any (physically realizable) frame of reference.

An electron and a tennis ball belong to situation (a), where as a photon belongs to situation (b)

Let us assume that two masses exist, the mass when object has zero speed 'm0' and mass 'm' when object has speed 'V' as observed in our frame of reference.

When the object has zero speed, it is at rest (as observed by us or by someone accompanying the object), and so 'm0' is called the object's rest mass. It is an intrinsic property of the object.

For instance every electron has rest mass m0=9.11 x 10^-31 Kg.

If we set into motion a tennis ball that is initially at rest, the ball acquires kinetic energy, the energy associated with motion.Its energy increases.

From the equation  E=mC2; it implies that increase in energy will correspond to increase in mass too. We deduce that ball's inertia increases. Thus the mass 'm' of moving ball is greater than the rest mass 'm0'. Hence m>m0 holds for any object with kinetic energy.

In 1905, Einstein summarized his theoretical discovery with sentence,

" The mass (i.e. the inertia) of a body is a measure of its energy content.  

 

What is wave motion?

Wave motion, in general refers to transfer of energy from one point to other point of medium.

For transfer of energy through a medium, the medium must possess the properties of
i) Elasticity ii) Inertia & iii) Negligible frictional resistance

and now the question is what propagates in wave motion?

It is not the matter that is propagated but it is only state of motion of matter that is propagated.
It may be said that in wave motion momentum and energy are transferred or propagated.


What is grounding?

Grounding is one of primary ways to minimize unwanted noise and pickup.

There are two basic objectives involved in designing good grounding systems.

i) To minimize noise voltage generated by currents from two or more circuits flowing thorugh a common ground impedance.

ii) To avoid creating ground loops which are susceptible to magnetic fields and differences in ground potential.

Grounding, if done improperly however, can become a primary means of noise coupling.

In most general sense a ground can be defined as equipotential point or plane which serves as a reference voltage for a circuit or system. By equipotential point we mean the point where voltage does not change regardless of the amount of current supplied to it or drawn from it. 

If the ground is connected to earth through a low impedance path, it can then be called an earth ground.

There are two common reasons for grounding a circuit:

i) For safety

ii) To provide an equipotential reference for signal voltages

Safety grounds are always at earth potential where as signal grounds are usually but not necessarily at earth potential.

In many cases, a safety ground is required at a point which is unsuitable for a signal ground, and this may complicate noise problem. 

  

Discovery of X-rays

Wilhelm Roentgen was professor of physics at university of Wurzburg, Germany when he discovered X-rays in 1985. The discovery was entirely serendipitous; Roentgen was merely studying a beam of electrons in a highly evacuated glass vessel. When the electrons, moving at great speed slammed into glass wall, they produced a very high penetrating radiation - a wholly unexpected occurrence. Roentgen first noticed the radiation when it caused a paper coated with Barium Platino-cyanide to glow. The chemical compound was a standard detector of UV light which causes the chemical to fluorescence i.e. to emit visible light after it has absorbed UV light. But Roentgen's evacuated vessel was tightly covered with black cardboard and so no UV light could emerge from it. The glow must be some other kind of radiation.

When he announced the discovery of the new radiation, Roentgen wrote:

"I posesss, for instance, photographs of ............the shadow of bones of hand, the shadow of a covered wire enclosed in a box.........."

Earlier in the paper, he noted that "the darker shadow of bones is seen with in the slightly dark shadow image of hand itself.

The new radiation quickly became a diagnostic tool in hospitals all over the world. Roentgen could not determine what the rays are made of and thus rays are named as X-rays.       

How is Neutron discovered?

In 1930, Bothe & Becker bombarded Lithium, Beryllium and Boron with alpha particles from Polonium and found a very penetrating but non-ionizing radiation, they assumed that the radaition was of gamma rays type because of its high penetration.

While repeating these experiments in 1932, Dr. F. Joliot and his wife, Dr. Irene Curie Joliot found that when a sheet of Hydrogen containing material, particularly paraffin, was interposed in the path of these radiations, Protons were ejected with a considerable velocity.

From the ranges of these recoil protons, the maximum proton energy 'E' proved to be about 5.3 MeV. Assuming that the protons were produced as the result of elastic collisions with the gamma ray photons, calculations showed that each photon must have possessed an amount of energy about 52MeV. These results were entirely inconsistent with the results from experiments on absorption of these in lead(about 7 MeV).

Chadwick, in England in 1932, after performing a series of measurements of energies of recoil of Protons ejected from thin targets by the penetrating "Be-radiation", with a pulse ionizing chamber and amplifier. He said, "these results are very difficult to explain on the assumption that the radiation from Beryllium is a quantum radiation, if energy and momentum are to be conserved in the collisions. These difficulties disappear, however, if it be assumed that the radiation consists of particles of mass 1 and charge 0 later named as Neutrons.          

These neutrons were formed as a result of highly exoergic nuclear reactions.

Three stage Indian Nuclear program


The three stages of Indian Nuclear Program

STAGE-1:
Construction of pressurised heavy water reactors. These reactors use natural Uranium. Spent fuel from these reactors is reprocessed to obtain Plutonium.

STAGE-II:
Construction of fast breeder reactors fuelled by Plutonium produced in stage-I. These reactors would also breed U-233 from Thorium.

STAGE-III:
Construction of power reactors using U-233/Thorium as fuel.

[click to enlarge]

What are Isomers?

In earlier days, if two half lives were observed in a given sample, it was assumed that two different isotopes were present, each decaying with particular half life.

One interesting example is isotope of Protactinium, Z=91, A=234 which is formed in beta decay of its parent, Thorium Z = 90, A=234[UX1]. The isotope of Protactinium was found to decay by the emission of beta particles of two distinct half lives, one of 1.18 min, the other of 6.6hr. It was assumed that these two half lives were due to two different isotopes and these were given separate names UX2 and UZ respectively.

In 1921, "Hahn" showed that these  two substances form a pair of Nuclear Isomers; i.e they are different energy states of same nucleus.

"Feather" and "Bretscher" later showed that these nuclear isomers are genetically realted; i.e. one type of nucleus is formed from other.


The nucleus called UX2 is an isomeric state of Pa-234 at an energy of 0.394MeV above ground state called UZ.

The nucleus may decay by beta particle emission directly from isomeric state of higher energy with a half life of 1.18 min or it may first emit a gamma ray photon of 0.394MeV, going to ground state of Pa, and then undergo beta decay to U-234 with a half life of 6.66 hours.

An isomeric state differs from ordinary excited state of a nucleus in that it lasts for measurable time.

Thus,

" Isomers are atoms which have same atomic number and mass number but differ from one another in their nuclear energy states and exhibit differences in their internal structure. These nuclei are distinguished by their different life times". 
 

Determination of Avogadro's number

Quantity of any substance whose mass, in grams, is numerically equal to its molecular weight is called a mole.

The volume occupied by a mole of any gas is called gram molecular volume. At 0oC and 76 cm pressure the gram molecular volume of any gas is 22.4 liters.

On the basis of Avogadro's hypothesis, every mole of a substance contains the same number of molecules. This number is referred to as Avogadro number.

Determination of Avogadro's number:

The behavior of electrolytic cells can be summarized in terms of two laws formulated by "Faraday".

First law:

It states that the quantity of any substance liberated from the solution depends only on the total charge passing through the circuit,

M = KQ; --------------------------------(1)

where 'M' is mass of material liberated at one electrode 
         'Q' is quantity of charge transferred
         'K' is factor of proportionality called electrochemical equivalent of the substance. It is mass   liberated per unit charge transferred, usually expressed in grams per coulomb.

Second law:

For any substance, the mass liberated by the transfer of quantity of electric charge 'Q' is proportional to chemical equivalent of substance,

M = (A/V) *(1/F)* Q  ------------------------(2)

where (A/V)  is the ratio of atomic mass to the valence of element, is the chemical equivalent of the element and 'F' is a constant of proportionality known as Faraday's constant.

From equations (1) & (2) it could be noted that

F = A/KV -------------------(3)

The value of 'F' can be determined from the results of experiments on electrolysis.

For case of silver, where K=0.0011180 grams/coulomb, A = 107.88 gms/gram atomic mass and 'V' is unity; we get

F = 96,500 Coulombs.gram atomic mass.

Thus the transfer of 96,500 coulomb of charge will deposit a gram atomic mass of a monovalent element. Since the valency of silver is unity, for every atom of silver deposited on the cathode, a charge equivalent to one electron has been transferred through the solution.

If 'e' is charge of one electron, then N*e is the total charge transferred when one gram atomic mass of silver is deposited on cathode.

F = N*e = 96,500 Coulombs/gram-atomic mass

hence N = 6.022 x 10^23 gms/gram atomic mass.

The first direct determination of Avogadro number was made by "Perrin" in 1908 in an investigation of motion and distribution of very small particles suspended in a fluid. 
 


  

What are PROMPT and DELAYED Neutrons in Nuclear Physics?

In the process of fission, the capture of a Neutron leads to formation of excited compound nucleus and thus breaks into two nuclear fragments having excess neutrons and energy of about 8 MeV which is sufficient to expel neutrons. Such neutrons which gets emitted in time scale of order 10^-14 sec are called prompt neutrons. They have energies of order of few MeV generally 1-2MeV.

     On the other hand, some fission fragments decay in various modes to become stable. In this process, fragments which undergo beta decay, some times forms product nucleus left in excited state with an energy more than average binding energy which then emits neutron to reach stable state. Aas this neutron emission follows beta decay of preceding nucleus and so neutron activity of that element will have some apparent half life due to beta activity of parent nuclide, usually of order of mSec to few Sec. This type of emission is called Delayed Neutron Emission and neutrons emitted are called delayed neutrons.     

You can see the decay scheme for two well known fission fragments Br-87 & I-137 exhibiting delayed neutron activity.

DELAYED NEUTRON EMISSION

 

(Click on images to Zoom)




ELECTROMAGNETIC SPECTRUM

Gamma Rays:

Wavelength Range:  from 0.0001 to 1Angstroms.

Production: Nuclear origin. Emitted on disintegration of nuclei of atoms.

Properties: Highly penetrating and uncharged. Exhibits fluoroscence, Phosphoroscence, ionization and chemical reaction on photographic plates.

Application: Gives information about structure of nuclei.

X-Rays:

Wavelength Range:  from 1 to 100 Angstroms.

Production: by striking high speed electrons on heavy target.


Properties: All properties of gamma rays holds good for these rays also, but less penetrating.


Application: helpful in medical diagnosis, study of crystal structure. 

Ultraviolet Rays:

Wavelength Range:  from 100 to 4000 Angstroms.

Production: by sun, arc, spark and ionized gases.

Properties:  All properties of X-rays but less penetrating. They produce photoelectric effect.

Application: used in medical applications. Detection of finger prints, forged documents. 


Visible Region:

Wavelength Range:  from 4000 to 7800 Angstroms.

Production: radiated from ionized gases and incandescent bodies.

Properties:  ehibit reflection, refraction, interference, diffraction, polarization, photoelectric effect.

Application: used in LASER technology.

Infrared radiation:

Wavelength Range:  from 7800 to 0.001 meter.

Production: by hot bodies.

Properties:  heating effect on thermopiles and bolometer. Exhibit refelction, refraction, and photographic emulsion.

Application: used in industry, astronomy & medicine etc.

Hertzian waves:

Wavelength Range:  from 0.001 to 1 meter.

Production: by spark discharge, by electronic devices such as Klystron & magnetron.

Properties:  reflection, refraction & diffraction. Produces spark in gaps of receiving circuits.

Application: used in radar and Masers and also to reveal finer details of atomic and molecular structure.

Radio waves:

Wavelength Range:  from 1 to 10000 meter.

Production: oscillating circuits and electronic devices.

Properties:  reflection, refraction & diffraction.


Application: used in television and radio broadcast system.





 

What is Loss of coolant accident in a Nuclear Reactor?

A loss of coolant accident (LOCA) is a mode of failure for a nuclear reactor ; if not managed effectively, the results of a LOCA could result in reactor core damage.

Every Nuclear power plant's Emergency Core Cooling System(ECCS) exists specifically to deal with LOCA.

When coolant flow is reduced, or lost altogether, the nuclear reactor's emergency shutdown is designed to stop fission chain reaction. However due to radioactive decay the nuclear fuel will continue generate a significant amount of heat.

The decay heat produced by reactor shutdown from full power is initially equal to about 5% to 6% of thermal rating of reactor.

If all independent cooling trains of ECCS fail to operate as designed, this heat can increase the fuel temperature to the point of damaging the reactor.  

How is blood pressure measured?

A person's arterial blood pressures are usually measured with the help of an inflatable cuff wrapped around the upper arm at the level of heart. A stethoscope is used to monitor the sound of the blood flowing through an artery below the cuff. The cuff is first inflated until the flow of blood stops then the pressure of the cuff is gradually reduced until the blood just begins to flow, which is recognized by a gurgling sound in the stethoscope. This pressure, called systolic, represents the maximum pressure the heart produces in the artery. The pressure in the cuff is then further reduced until the gurgling stops, which corresponds to the restoration of normal blood flow. The pressure at this time, called diastolic, represents the pressure in the artery between the contractions of the heart.   

Physicians express blood pressures in torr, where 1 torr is the pressure exerted by a column of mercury 1 mm high; it is equivalent to 133Pa. The torr was formerly referred to as the "millimeter of mercury", abbreviated mm Hg. The unit is named after Evangelista Toricelli (1608-1647), the Italian Physicist who invented the barometer, which measures atmospheric pressure. Average atmospheric pressure is 760torr. In a healthy person the systolic and diastolic blood pressures are, respectively, about 120 and 80torr.   
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How does particular metal crystallize to particular structure?

The reason for a particular metal to crystallize in a particular structure must be sought in the fact that the free energy E-TS for this system is lower than that for any other structure.

The same remark may be made with reference to those metals which have different structures in different temperature regions(Allotropy). This phenomenon is exhibited especially by three and four valent metals and by the transition metals.

For instance, Alpha Iron(BCC) is stable upto 910 deg.centigrade; between 910  and 1400 degree Centigrade the stable structure is gamma Iron(FCC); between 1400 and the melting point (1530) the structure is again BCC( Delta iron).

The transformation from one structure to another is dictated by the requirement of minimum free energy. This does not mean that such transformations takes place as soon as the existing structure becomes unstable.

In fact, a transformation of structure involves a rearrangement of atoms, and such a process may take a long time. The reason is that even though the free energy after the transformation is lower than in initial state, the two states are usually separated by an energy barrier or activation energy.

Thermodynamics specifies only the equilibrium condition but doesn't give any information about the velocity of reaction or processes involved in establishing equilibrium. From the atomic point of view, the stability of crystal structures is a problem of cohesive energy, involving the interaction between the atoms.      


Difference between "Mass" "Matter" and "Energy"

Well the fancy of the subject "physics" is unexplainable. Understanding of basic terminology gives immense satisfaction. 

How many of you could differentiate the three terms "Matter", "Mass" & "Energy" which are essential for beginning understanding of physics? 

Let us start explaining things:- "Mass" is an attribute and not a physical thing. Mass is the attribute "inertia" of a physical object or of what ever is contained in a specified region of space. 

"Inertia" is the inherent reluctance to undergo a change in velocity. If one consults the research documents of decade 1900-10, when Einstein and others developed the equation E=mc2, one finds that for those physicists- the word "Mass" was synonym for "inertia". 

"Matter" is tangible stuff; What you can touch and sense with your hands and so a physical thing.Hence all matter has inertia and hence has mass. 

 "Energy" is the ability to do work. It is an attribute to physical object or of whatever is contained in a specified region of space. Three general forms for existence of energy are "Kinetic", "potential", "Radiant". "Kinetic" is the energy associated with motion. 
"Potential energy" is the energy that has potential for being converted to kinetic energy. 
"Radiant energy" is energy of Electromagnetic waves. 

Take a stone and throw into air. The stone which you are able to collect it from ground has got matter as you have touched and sensed it. While moving in air the stone doesn't get blown by wind breeze etc and does possess "inertia". It is moving with a velocity and does has Kinetic energy, at the same time it is at a varying height from ground and hence possess gravitational potential energy.Thus the stone in air has got partly kinetic energy and partly potential energy. Thus "mass' and "energy" exist as attributes of a physical system, just as do color or shape. Mass and energy exist in the same fashion and matter exists in different fashion. Hope this benefits the student community.......Have a nice day

How do we define Glass?


There are number of definitions of glass which have different approaches. 

There is no universally accepted or universal definition of glass. 

It is a fusion product of materials which have been cooled to a rigid condition with out crystallization(It need not be inorganic). 

Examples of familiar glasses made from cane sugar are lollipops and cotton candy. The former are in shape of rigid block and latter are flexible fibers.

Other definitions: 

1) An Amorphous solid or glass is one in which long range order is absent and the array of equilibrium atomic positions is strongly disordered. 

2) Glass is an uncrystallized solid material. 

3) Glass is an inorganic product of fusion which has been cooled to a rigid condition with out crystallizing. 

4) A general definition including all the aspects of glass is not possible; glass is to be conceived on one hand as a physical chemical condition and on other hand as a technical material.

Why to use Fuse?

Any electrical or electronic appliance is designed to take specified current. Under some circumstances, there may be drawing of larger currents by then then what they are rated for.

For instance too many appliances connected simultaneously in a circuit causing the total current drawn to be higher than can be handled by wires. This is called overloading.

The higher current due to short circuits or overloading can damage the appliances and the electric wires may even catch fire. To avoid this risk, a safety device called "Fuse" is used in series with the circuit.

A fuse is a short piece of wire of low melting point which is connected in series between Mains and the Appliance. When the current rises above the safe limit the fuse wire gets melted and makes the circuit open.
Design aspects of fuse like: Material of  wire, Dimensions etc are selected based on the safe limiting of current required.

                  

Electric power & Energy

Electric Power


Electric power is the electric work done per unit time.

1 Watt = 1 Joule / 1 Second

Though Watt is unit of power, it is too small for measuring domestic consumption of electricity. Thus we use a larger unit of power called Kilowatt.

Electrical Energy


It is usually measured in a unit called Kilowatt hour(KWh) which is amount of electrical energy consumed when an electrical appliance with a power rating of 1 KiloWatt is used for 1 hour.

1 KWh= 3.6 x 10 ^ 6 Joules

Power Rating of Domestic Appliances

The power rating of an electrical appliance tells us the rate at which the appliance uses electrical energy.
An electric iron box marked 220V, 1000W has a power consumption of 1000W at 220V AC, i.e it consumes electrical energy at the rate of 1000Joules per second when a potential difference of 220V is applied across it (which is potential difference at which electricity is supplied to our homes).  

The electrical energy consumed (in KWh) by an electrical appliance is given by the product of its power rating (in KW) and the time for which it is used(in hrs).

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How does a Light Emitting diode (LED) work?


Light Emitting Diode (LED) is always operated in forward bias mode.


Direct band semiconductors are used for LEDs.

Before applying voltage




After applying voltage



At sufficient voltage, electrons gain sufficient voltage so that they combine with holes to give light which has color that depends on energy gap of chosen semiconductor.

The wavelength of emitted light depends on energy gap and is expressed as 1.24 / Eg; where Eg is energy gap.


Equivalent circuit of a capacitor

The equivalent circuit of an actual capacitor shown below indicates that there are other characteristics besides capacitance to be considered.

i) Inductance (L) of the leads and plates
ii) Resistance (R1) of dielectric (leakage resistance)
iii) Resistance (R2) of leads and plates (effective series resistance)
iv) C is measured capacitance





Is there energy associated with intrinsic inertia, the rest mass?

We could have the object at rest to annihilate with an "anti-object", producing radiation possessing energy.
So, yes, there is energy associated with the rest mass.

while creating an atom, various particles like electrons, protons, neutrons are to be brought in together. Every bit of energy that goes into creating the object would be accompanied by an increase in inertia.

According to relation E = ΜC^2

The following figure sketches this symbolically. Starting from zero for both the object's energy and its inertia and adding up increments, we emerge with E=MC^2.



The attribute energy is always accompanied by attribute inertia.

In 1905, Einstein summarized his theoretical discovery with the sentence,

" The mass [i.e inertia] of a body is a measure of its energy content."

Energy , in all forms has property of inertia, the reluctance to undergo a change in velocity. The more energy that went into forming a body, the more inertia the body has.  


Definition of Ampere

It is the constant current which, if maintained in two straight parallel conductors of infinite length and of negligible cross-section and placed one meter apart in vacuum, would produce between these conductors a force equal to 2 x 10 ^ -7 N/m of length.



How is it proved that alpha rays are nuclei of Helium atoms?


The identification is made by Rutherford and Royds in 1909. By spectroscopic method, they found traces of Helium in a pure sample of Radon gas, which is an alpha emitter. When an electric discharge was passed through a tube containing pure radon gas, initially only characteristic Radon lines appeared.

After a day, Rutherford found that Radon lines became somewhat weaker and new lines started appearing. These new lines were identified with Helium spectrum. As the days passed, the Radon spectrum began weakening while Helium lines grow brighter.

Thus, for first time, people saw decay of an element (Radon) and birth of a new element, Helium nuclei. Such a transformation in which a parent element gives rise to a new element called daughter product by emitting radioactive rays is called radioactive transformation.



What are nano materials?

These are materials whose dimensions are less than 100nm. They act as one dimensional systems or zero dimensional.For comparison, a human hair is about 50,000nm in diameter, while a smoke particle is about 1000nm in diameter.

The term nano materials is less specific since it refers to coatings that are less than 100nm.

The nano particles consist only thousands of atoms. They are called quantum dots.

Methods of Synthesis of Nano Structured Materials:

Synthesis and assembly strategies can be accommodated from Liquid, Solid or Gas Phase

i) By employing chemical or physical deposition approaches.

ii) Relying on either chemical reactivity or physical compaction to integrate nano structure building blocks to form final nano material structure.  

Variety of techniques are
i) Assembling from nano building blocks
ii) Powder/Aerosol compaction
iii) Chemical Synthesis
iv) Mechanical attrition
v) Lithography/Etching

These above techniques can be classified into two approaches:

i) Bottom up Approach: Here first building blocks are formed and then assembled to form final material.

ex:- Aerosol /Powder technique in which powder components are compacted into final material.

This approach has been widely used in formation of structural composite materials.

ii) Top-Down Approach: Here first a suitable nano material is taken and then sculpted according to functionality of material. This approach is very similar to techniques employed semiconductor industries in forming devices from electric substrate by etching a pattern from it.Lithography/etching, Ball milling fall in this category.

Classification of Nano Crystalline Materials:

i) Nano crystalline materials are single phase or multi phase poly crystals, the crystal size of which is of order of few (1-100nm) is at least one dimension.

ii) They can be equiaxed and can be formed nano strucuture Crystallites -3D nano structures

iii) They can consist of lamellar structure and will be termed as layered nano structure-1D

iv) They can be filamentary in nature - 2D

v) They can be clusters or cluster assembly - 0D 

Why statistical mechanics was introduced?

When we consider bodies at macroscopic level they consist of uncountable atoms or molecules i.e about 10^23 atoms/gm mole. In such cases we cannot predict the result of interactions between atoms with the help of ordinary classical laws of motion. In order to solve such a situation, a new branch of science called statistical mechanics is introduced.

Statistical mechanics is the branch of science which establishes the interpretation of macroscopic behavior of system in terms of its microscopic properties. It doesn't deal with motion of each particle but it takes into account the average or most probable properties of system with out going into interior details of characteristics of its constituents.

The larger the number of particles in the physical system considered, the more nearly correct are statistical predictions.

Before the advent of quantum theory, Maxwell, Boltzmann, Gibbs etc applied statistical methods making the use of classical physics. These statistical methods are known as "classical statistics" or "maxwell boltzmann statistics".

These statistics explained successfully many observed physical phenomenon like temperature, pressure, energy etc; but couldn't explain adequately several other experimentally observed phenomenon like black body radiation, specific heat at low temperature etc.

In order to explain such phenomenon "quantum statistics" was introduced and developed by Fermi, Dirac, Bose, Einstein with new approach by using new quantum idea of discrete exchange of energy between system.