Metabolism

All chemical changes occurring in a living cell are called metabolism. Metabolism may be anabolism or catabolism. Anabolism is the process of synthesis of complex chemical molecule from simpler ones. Photosynthesis is an example of anabolism. Catabolism is the process of breaking down of a large and a complex molecule into the simple form. Respiration and digestion are the example of catabolism .

Anabolism and catabolism together are called metabolism . Anabolism is called a constructive process and catabolism is called the destructive process. Metabolism is indicated by the following processes taking places in the body.

a.      Formation of the necessary cells and tissues takes place in the body  as a result of the chemical reaction of various nutritious food.

b.      The blood cells and tissues  become useless  in the body .

Nutrition in the Human body:

Human beings like other animals are unable to prepare their own food so, the nutrition in the human beings is heterotropic. The human being depend on plants directly or indirectly for their food.

Digestive System in Human:

Digestion is a catabolic process or the process of breaking down of complex food materials into simple forms which can  be directly absorbed by the body. The organs concerned with digestion is called digestive system. The digestive system of human body consist of mouth, alimentary canal and the anus.

Mouth:

It is an opening through which food is taken inside the body. The food mixes with saliva inside the mouth and here the mechanical break down food occurs by the help of teeth and tongue. Saliva contains the enzyme ptyalin which helps to break down the carbohydrate partially to the glucose.

Alimentary Canal:

The alimentary canal is basically a long tube extending from the mouth to anus. It is necessary to move the foods in a regulated manner along the digestive tube so that it can be processed properly in each part .  The linings of canal have muscles that contract rhythmically in order to puss the food forward. These peristaltic movements occur all along the gut. Alimentary canal has the following parts:

a.      Food pipe or oesophagus

b.      Stomach

c.       Small intestine

d.      Large intestine

e.      Anus

Food Pipe or Oesophagus:

The food after chewing in the mouth passes to stomach through the food pipe or oesophagus.

Stomach:

The stomach is a large organ which expands when the food enters in it. The muscular walls of stomach helps in mixing the food thoroughly with more digestive juices. The digestive functions are carried out by the gastric glands present in the wall of stomach. The gastric gland release:

a.      Hydrochloric acid

b.      A protein digesting enzyme called protein

c.       Mucus

The hydrochloric acid creates an acidic medium which facilates the action of enzyme pepsin. It also kills the bacteria present in the food.

Life Insurance

Life insurance is intended to bear the insurance against unexpected financial losses caused by the death of his too fast or too long . Here illustrated that in life insurance, the risks faced are :

The risk of death Someone living too long This is, of course, will bring a lot of aspects, if the risks inherent in a person is not insured with insurance companies. For example guarantee for offspring, a father that died prematurely or with a sudden , the child will not be neglected in his life .

It could also happen to a person who has reached the age ketuaannya and not being able to earn a living or pay for their children , then buy life insurance, the risks that may be suffered in terms of lost opportunities to earn a living will be covered by insurance companies . It turns out here that do good life insurance agency with the primary objective is to assume or guarantee the person against financial losses .

Life insurance is a legal contract between two parties, namely the insurance company and the policyholder . This ensures that the recipient receives financial support in the event of the insured 's death or accident . Term insurance policy states that the policyholder agrees to pay a certain premium at regular intervals .

Life insurance depends on a number of factors, including age, income, expenses, loans, number of dependents, health, etc. It is mainly of four different types, universal life insurance, term life insurance, whole life insurance, life insurance and endowment . Described in detail below is offering life insurance benefit . In general, the insurance system offers you a solution where you can guarantee your future financially and Life Insurance offers some kind of solution to the needs of your life in the future. This type of insurance is also available in various types and the choice depends on your needs.

Thankyou!! for reading the above Post. If You have any questions or any things related to above topic then please comment below !!!

Auto Insurance

This insurance is something that all drivers must get all day, every day when driving out and on the road. Nowaday, everyone is obliged to have accident protection most in every U.S State. Here are 5 great reasons not to think like "goodness, its alright, i never hit anybody in my life"

1. On the off chance that you don't have your evidence of having collision protection scope when the cop appeal, be arranged to pay for an enormous fine! It totally will be at any rate $500 or more. Regardless of the fact that you have your verification of accident protection, you ought to dependably keep it in your auto all day, every day when you're out and about. Since on the off chance that you don't, be arranged to have your reference closed down by a cop, then bring it to your neighborhood court and pay $10. At the same time recall to verify you accomplish it whenever in the eyes of your court date that is composed on your ticket. I'll let you know a decent motivation behind why! In the event that you miss your first court date, the $10 will be $370 in fine. What's more in the event that you miss your second court date, the $370 will be near to $1000 in fine. Trust me or not, it did befall me.

2. When you get into a pile up with you at flaw and without accident protection, you are going to be in a bad position with the DMV and your fianance when the police come to do the mischance report. First and foremost, you may get your auto towed and permit suspended in the event that you tell the cop that you don't have collision protection scope. On the second, you will likewise need to pay for expense of all harms brought about in the mishap, which are the settling expense for the auto of the individual you hit and the expense of remuneration for his or her damage if created by the mischance. Also believe me on this, 95 percent of the time you will, regardless of the possibility that that individual is not by any stretch of the imagination harming or experiencing the mishap. He or she could at present go to the specialist to have examination or treatment, and the more drawn out the treatment last, the more cash you're going to pay. Taking into account what i evaluated as the normal, one minor mishap without anybody getting damage will at any rate cost you $10,000. Be that as it may in real mishap when somone is truly harmed or injuried that he or she must be hospitalized, i'd say its in the scale of $30,000 - $100,000 that you will need to pay. Also you will go to prison in the event that you don't pay for it.

3. It's generally sheltered to realize that you are protected for yourself as well as for other individuals around you. You could simply feel safe and not stressed realizing that you have accident coverage scope. Accident protection Coverage doesn't generally cost that much in case you're a decent driver with no tickets or any at issue mischances. Espeically for youthful young driversarticle Submission, it could cost generally as low as your telephone bill on the off chance that you know the right accident coverage organizations.

Language of Chemistry

The universe is composed of matter and energy. Matter and energy are inter-convertible to each other. The branch of modern science which deals with the study of composition, transformation and property of matters is known as Chemistry. Chemistry can be classified as:

a.      Physical Chemistry

b.      Iorganic Chemistry and

c.       Organic Chemistry

Element:

An element is defined as pure substance which can neither be decomposed into nor built from simpler substance by any kind of physical or chemical methods. Eg: Hydrogen, Oxygen, Carbon, Sodium etc. The concept of element was first introduced by Robert Boyle.

Atom:

The smallest particle of an element which can take part in chemical change is called an atom. It may or may not be capable of independent existence.

Compound:

A Compound is a substance produced by union of two or more elements in a definite proportion. t can be decomposed into two or more simple substance. Eg:

Water- H2O

Glucose- C6H12O6

Ammonia- NH3 etc.

Molecule:

A molecule is defined as the smallest unit (particle) of any kind of substance, elements or compounds which can exist independently and can possess all properties of substance. Eg: H2, O2, O3, P4, S8, H2O etc.

Homonuclear Molecule: Molecule formed by the combination of similar kinds of atoms are called homonuclear molecule. Eg: O2, O3, P4, S8 etc.

Heteronuclear molecule: Molecule formed by the combination of different kinds of atoms of different elements are called heteronuclear molecule. Eg: CH4, PCl5, H2O etc.

Symbol: Symbol is defined as the abbreviation or shorthand sign for the full name of an element. One or more letter(s) is used to write the symbol of an element.

Eg: Hydrogen        H                                                                                                                                      

      Oxygen            O

      Magnesium     Mg

      Uranium           U

      Vanadium        V

      Antimony         Sb

      Gold                  Au

      Curium             Cm

      Nobelium         No

      Americium       Am

      Plutonium         Pu

Valency:

Valency of an element is the combining capacity of the element which is measured in terms of hydrogen atoms or its equivalent which combine with one atom of that elements. Examples:

Elements       Valency

H                       1

O                      2

N                      3

Al                     3

Ca                    2

Na                    1

Certain elements can have more than one valency that is they exhibit variable valency. Eg:

Fe-  2 and 3

Cu- 1 and 2

Sn- 2 and 4 etc.

The compound in which the metal has lower valency is called an “ ous “ compound while the compound in which the metal has higher valency is called “ ic “ compound.

Eg: Fe= 2 valency FeCl2, Ferrous chloride

      Fe= 3 valency FeCl3, Ferric chloride

Radical:

A radical may be defined as an atom or group of atoms having positive or negative charge and behaves as a single unit in chemical change.  

Some Common Radicals

Monovalent Radicals

1.  Ammonium       NH4

2.  Hydroxide         OH

3.  Cyanide              CN

4.  Nitrite                NO2

5.  Chlorate            ClO3

6.  Amide               NH2 etc.

Divalent Radicals:

1. Carbonate        CO3

2. Oxalate              C2O4

3. Sulphite              SO3

4. Zincate               ZnO2

5. Stannite             SnO2

6. Stannate          SnO3 etc

Trivalent Radicals:

1. Aluminate         AlO3

2. Arsenite            AsO3

3. Arsenate           AsO4

4. Ferricyanide     Fe(CN)6 etc.

Dalton’s Atomic Theory: (John Dalton, In 1808)

Postulate:

1.      All matter consists of extremely small individual particles called atoms.

2.      Atoms of same elements are all alike.

3.      Atoms of different elements are entirely different and have different properties.

4.      Atoms can neither be created nor be destroyed, it can only be transformed to one form to another.

5.      Atoms combines together in simple whole number ratio to give compounds.

6.      The relative number and kinds of atoms are constant in a given compound.

Stoichometry:

Stoichometry is the branch of chemistry which deals with the weight relationship in chemical reaction and weight relationship that prevails in a chemical compound.

Law of Chemical Combination:

1.      Law of conservation of mass

2.      Law of definite proportion

3.      Law of multiple proportions

4.      Law of reciprocal or equivalent proportions

5.      Law of gaseous volume

Internal Commands

        

Time:  This is an internal command. It is used to display current time and also set a new time.
Eg: C:\>time (press enter)

Date:  This is also an internal command. It is used to display current date and also set a new date. The date is shown in the mm-dd-yy format. Eg:  C:\>date (press enter)

Ver: This command is used to display the version number of your computer. Eg:  C:\>ver (press enter)

Vol: This command is used to display the volume serial number of your computer. C:\>vol (press enter)

Cls: (clear logical screen) This command is used to clear the screen. Eg:  C:\>cls  (press enter)

DIR: This command is used to display all the files and directories in your computer. Eg:  C:\>DIR (press enter)

C:\>DIR/P (press enter) : It is used to display files and directories page wise.
C:\>DIR/W (press enter): It is used to display files and directories width wise.
C:\>DIR/AD (press enter): It is used to display only directory.
C:\>DIR/A-D (press enter): It is used to display only files.
C:\>DIR/S (press enter): It is used to display all files and directories of the computer.
Note: Press ctrl+C (key) to stop running files and directories.
(Note: Here, Capital U means space)
C:\>DIR U ??? (press enter): It is used to display those files and directories which have upto 3 characters.
C:\>DIR U* com (press enter): It is used to display those files which have com as an extension only.

File: A collection of information can only be saved in the form of file. Hence, a collection of related information saved in the computer is called a file.

Copy con command: This command is used to make a new file in the computer. Syntax: C:\>copy U con U filename  (press enter)
( Note: Press F6 or ctrl + Z key for save then press enter key )

Type command: The type command is used to display  contents of file. Syntax: C:\>Type U filename (press enter)
Eg:  C:\>Type U Golden (press enter)

DEL (DELETE) or Erase: The DEL command is used to delete (remove) your selected file from the computer. Syntax: C:\>DEL U filename (press enter)
                                  C:\>Erase filename (press enter)

Ren (Rename) command: The Ren command is used to change the filename.
Syntax: C:\>Ren U old filename U new filename (press enter)

Copy command: This command is used to make duplicate file. It is used to combine two or more files. It is also used to copy the file from one disc to another disc.

To make duplicate file:
Syntax: C:\>copy U old filename U new filename (press enter)

To combine the file:
Syntax: C:\>copy U F1 + F2 + F3 U new file name (press enter)

To copy the file from one disk to another disk:
Syntax: C:\>copy U filename U drive name (press enter)

Note: Here, Capital (U) means to give space.

Prompt command: The prompt command is used to change the prompt (C:\>).
C:\>prompt $T  (press enter): It is used to display current time.
C:\>prompt $V (press enter): It is used to display version number of your computer.
C:\>prompt $Q (press enter): It is used to display equal sign.
C:\>prompt $B  (press enter): It is used to display (;) sign.
C:\>prompt $G  (press enter): It is used to display greater than (>) sign.
Type $P $G key then press enter key to display C:\>.

Directory: A table of contents on the disc is called a directory. A directory within a directory is called sub-directory.

MD (Make Directory): The MD command is used to make a new directory.
Syntax: C:\>MD directory name (press enter)

CD (Change Directory): The CD command is used to change the directory.
Syntax: C:\>CD directory name (press enter)

RD (Remove Directory): The RD command is used to remove the directory.
C:\>RD directory name (press enter)
Note: If you want to remove directory then you should remember following points:
Directory must be empty and
Exit from the current directory.

Exit command: This command is used to return the windows screen.
Eg: C:\>exit (press enter)

Thankyou! For viewing and reading this article.

Death of a Star

Universe is made up of many different elements. Stars are also one of the element of this Universe. As we know, if the sky is clear then we see many uncountable stars are twinkling at the night time. Have you ever noticed or had a knowledge that stars are born and also they die after certain interval of time. Now in your mind many questions have been raised such as Do the stars are really born? Do they really die? Do these things really happen? After reading this article you will know everything from the born upto death of Stars and afer that also what happens.

When a star is born, its hydrogen goes on being used in fusion. When the hydrogen fuel is exhausted, the outward pressure created by the nuclear reactions ceases and the gravitational force within the star predominates. The star goes on contracting. Due to the contraction, the core temperature rises which causes the expansion of the outer layers of the star. The expansion causes cooling effect. The result is that size of the star grows and the temperature falls. Ultimately, a stage is reached at which the star becomes very large in size and red in color and it is called Red giant. This red giant lasts for millions of years and at its end, the star begins emitting energy at tremendous rate for which the helium becomes the fuel. At the end, a violent explosion called nova/supernova occurs. Due to this explosion, large portion of the stars envelop is thrown into the interstellar space which ends the existence of the star and the star is dead.

 Now, there are three types of dead bodies of stars and they are:
 a. White dwarf
 b. Neutron star and
 c. Black hole

The red giant initially having mass less than 2 Ms (mass of the sun) cools to change its color from white to yellow, yellow to red and finally disappears and its mass becomes equal to that of the earth. This is known as White dwarf.

When the mass of the star is greater than 2 Ms and less than 5 Ms, contraction collide with protons to produce neutrons and eventually the stars becomes full of neutrons. This is known as Neutron star. It does not emit light, but sends out radio waves in the form of pulse. So they are also known as Pulsars. They have a diameter of about 10^-20 km, density 10^17 kg/m^3 and produce intense magnetic field of the order of 10^8 T.

The massive star having mass more than 5 Ms, undergoes uncontrolled contraction because of inward pull of its own gravity. The star becomes so dense that nothing even light can escape from its gravity. This is known as black hole. It is a very large amount of matter packed in a small area. Think of a star 12 times more massive than the sun which is squeezed into a sphere approximately the diameter of Kathmandu city. The result is a gravitational field which is so strong that nothing, even the light cannot escape through it.

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The Laser

The word laser stands for “Light Amplification by Stimulated Emission of Radiation”. The laser is a device that produces an intense beam of coherent monochromatic and unidirectional light as a result of co-operative emission from many atoms. This light beam may be intense enough to vaporize the hardest and most heat-resistant materials.

Principle of Laser:

Consider an assembly of atoms of some kind that have metastable states of excitation energy hv. Suppose we somehow raise a majority of the atoms to the metastable level. If we now shine light of frequency (v) on the assembly, there will be more induced emission from the metastable level than the induced absorption by the lower level. Thus, the result will be an amplification of  the original light. This is the concept that underlies the operation of the laser.

Population Inversion:

Under ordinary conditions of thermal equilibrium, the number of atoms in the higher energy state is considerably smaller than the number in the lower energy state (Since, by the Boltzmann law, N2/N1 = e^{(E2-E1)/kT} i.e., N2<N1. Hence there is very little stimulated emission compared with absorption. Let, by some means, the atoms be initially excited so that there are more atoms in the higher energy state E2 than in the lower energy state E1. Then we have N2>N1. This is known as Population Inversion.

Pumping:

The method of producing population inversion is called pumping. One type of pumping is "optical pumping". Consider a material whose atoms can reside in three different states as shown in figure (a). Atoms in ground state are pumped to state E3 by photons of energy hv' = E3-E1. The excited atoms then undergo non-radiative transitions with a transfer of energy to the lattice thermal motion, to the level E2. They remain in this metastable energy state for a comparatively  long time. Thus there will be more atoms in the higher metastable energy state E2 than in the ground state E1, i.e., we have a "population invertion", atoms in the metastable state E2 are now bombarded by photons of energy hv = E2-E1, resulting in a stimulated emission giving an intense, coherent beam in the direction of the incident photons. This is the method used in the ruby laser.

Mainly, Laser are of three types:

a. Ruby Laser

b. Helium-neon Laser

c. Semiconductor Laser

 

a. Ruby Laser:

It consists of a ruby cylindrical rod whose ends are optically flat and accurately parallel (figure c). One end is fully silvered and the other is only partially silvered. The rod is surrounded by a glass tube. The glass tube is surrounded by a helical xenon flash tube which acts as the optical pumping system.

The energy level diagram of these chromium ions is shown in above figure (c). The Cr ions are excited from level E1 to level E3 by the absorption of light of wavelength 550 nm from the xenon flash tube. The excited ions quickly undergo non-radiative  transitions with a transfer of energy to the lattice thermal motion, to the level E2. The E2 level is a metastable state with a lifetime of about 3 * 10^-3 (usual atomic life times are nearly equal to 10^-8 s). Now, the population of E2 level becomes greater than that of the E1 level. Thus “population inversion” is achieved.
Some photons are produced by spontaneous transition from E2 to E1, and have a wavelength of 694.3 nm (ruby red). The ends of the ruby rod act as reflecting mirror. Therefore, photons that are not moving parallel to the ruby rod escape from the side, but those moving parallel to it are reflected back and forth. These stimulate the emission of similar other photons. The chain reaction quickly develops a beam of photons all moving parallel to the rod, which is monochromatic and is coherent. When the beam develops sufficient intensity, it emerges through the partially silvered end.

Once all the chromium ions in the metastable level have returned to the ground level, the laser action stops. It is necessary to send one more flash of pumping radiation through the rod. Thus the ruby laser operates only in pulses.

b. Helium-neon Laser:

He-ne laser is a type of laser which consists He  and Ne in the ratio of 5:1 and also work with  the principle of laser operation.

Construction of He –Ne laser:

It consists of laser tube of approximately 5 mm in diameter and 0.5m long .It contains a mixture of helium and neon in the ratio of 5:1 at a total pressure of about 1 torr. The tube has parallel mirrors, one of them is partly transparent at both ends. The spacing of the mirrors is equal to an integral number of half wavelengths of laser light. The tube contains two electrodes which are connected to high voltage power supply so that electric field is set up in the tube. The mixture of the gas is ionized by passing electric current through it.

Working:

When the power supply is switched on, the electric field is setup in the tube. Helium atoms are excited very efficiently by electron impact into the 2s level as in the figure while the neon atoms are much readily excited by the electrons. The excited 2s state of helium is relatively long lived. The energy of this level(20.61 eV) is almost the same as the energy of the 5s level in neon (20.61 eV). Hence the energy of the helium atoms is easily transferred to the neon atoms when they collide. This preferential transfer of the neon atoms to the 5s state results in a population inversion between the 5s and 3p states. The purpose of the He atoms is thus to help achieve a population inversion in the Ne atoms. The spontaneous transitions from the 5s state to the 3p state, produce photons of wavelength 632.8 nm, which then trigger stimulated transitions. Photons travelling parallel to the tube are reflected back and forth between the mirrors placed at the ends, and rapidly build up into an intense beam which escapes through the end with the lower reflectivity. The Brewester end windows allow the light of one polarization to pass through without any reflection losses. Because the electron impacts that excite He and Ne atoms occur all the time. Thus, He-Ne laser operates continuously.

c. Semiconductor Laser:

Semiconductor Laser are those laser which are compact, efficient and can be fabricated with ease, however their monochromaticity, coherence and directionality are inferior to those of other lasers.   

Properties of a Laser Beam:

a.    The light is very nearly monochromatic.

b.    A laser beam diverses hardly at all.

c.    The light  is coherent with the waves all exactly in phase with one another.

d.    The beam is extremely intense.

Applications of Laser:

The laser is used in holography, radio communication in outer space, piercing holes in metals, detecting and ranging objects at great distances, welding, surveying  and delicate surgery.

Motion And Its Laws

 Newton proposed three laws of motion:

i. Newton's first law of motion:
Everybody in the universe will remain in the state of rest or of uniform motion in a straight line unless no external force act on it. It gives the defination of force as "force is that external agent which changes or tends to change the state of rest or of uniform motion in a straight line".
Inertia is the tendency of a body to remain in its own state unless external force act on it. It is divided as:
a) Inertia of rest
b) Inertia of motion and
c) Inertia of direction
     Hence, Newton's first law of motion is also called Law of inertia.

 Momentum (P):
 The quantity of motion contained by a body which is equal to the product of mass and velocity is known as momentum.
   Therefore, Momentum(P) = m * v
  It is a Vector quantity.

ii. Newton's second law of motion:
It states that "the rate of change in momentum of a body is directly proportional to the force act on a body and displacement takes place in the direction of force".
    Therefore, force (F) = dp/dt
                                    = d(mv)/dt
                                    = mdv/dt + vdm/dt
    If m is constant then, F = ma
    If v is constant then, F = vdm/dt

iii. Newton's third law of motion:
It states that "for every action there is equal and opposite reaction". Action and reaction act on two different bodies so they never cancel eachother.

2. Impulse:
 The net effect of force acting on a body is measured by a quantity called impulse.
Hence, impulse (I) = P2 - P1 = Change in momentum.

3. Motion in a lift:
  When a person of mass (m) is standing on the floor of lift at rest R = mg is called weight of a person. For uniform motion of a lift a = 0 so,
 Net force = R - mg = ma
or, R - mg = 0
or, R = mg

 i. When lift is accelerating upward:
 When lift is accelerating upward with an acceleration (a) then,
R - mg = ma
or, R = mg+ma

 Reaction of floor measure the apparent weight of body which increases.

 ii. When lift is accelerating downwards:
  When lift is accelerating downwards with an acceleration (a) then,
mg - R = ma
or, R = mg - ma

 Reaction of floor decreases hence apparent weight of person body decreases.

4. Principle of conservation of linear momentum:
   When no external force act on the system of colliding bodies then the total linear momentum of system remains constant (conserved).
 Therefore, F = dp/dt
If F = 0 then, dp/dt = 0
hence, P = constant
or, mv = constant.
  If  two bodies of mass m1 and m2 moving with u1 and u2 collide then their velocities changes to v1 and v2 respectively then,
 m1u1 + m2u2 = m1v1 + m2v2
When two bodies move together after collision then,
 v = (m1u1 + m2u2) / (m1 + m2)


5. Free body diagram:
 While solving the problems relating the newton's law of motion, free body diagram is used. During free body diagram,only the body of our consideration is taken an all the process acting on it are drawn. The net force acting on a body gives the acceleration so, F1 = ma.


6. Rocket propulsion:
 The propulsion of rocket is based on the principle of conservation of linear momentum or newton's third law of motion. A rocket of initial mass M1 eject combust fuel at the rate of dm/dt at any instant at which M be the mass of rocket the velocity of ejected gas relative rocket is v then,
  i. Force on a rocket due to ejection of gas in absence of gravity is, F = dm/dt * v
  ii. Full acceleration on rocket due to this force is, a = F/M = dm/dt * v/M
  iii. Net force on rocket due to gravity, F = dm/dt * v - mg
  iv. Acceleration on rocket in gravity is, a = F/m = dm/dt * v/m - g

X-Rays

X-Rays were discovered by Roentzen in 1895. X-Rays are electromagnetic waves of short wavelengths in the range of 10Å to 0.5Å. They are produced when electrons with high speed strike a metal target of high atomic weight. The longer wavelength end of the spectrum is known as “soft x-rays” and the shorter wavelength end is known as “hard x-rays”. X-Rays are also called as Roentzen rays. All of them are not of single wavelength. Different X-rays have different wavelength but lines within the range.

Soft X-Rays:
a. Have long wavelength
b. low energetic and low penetrating power
c. wavelength above 4Å.

Hard X-Rays:
a. having short wavelength
b. more energetic and high penetrating power
wavelength is below 4Å.

 X-Rays Production:

X-rays are produced when fast moving electrons are suddenly stopped by a solid target. A coolidge tube is shown in the figure below:

The tube is exhausted to the best possible vacuum of the order of 10^-5 mm of mercury. The cathode consists of a tungsten filament (F) heated by a low tension battery. Thermoionic electrons emitted by a filament are accelerated towards a target (T) by a high P.D maintained between F and T. The filament is placed inside a metal cup G to focus the electrons on to the target. The target must be cooled to remove the heat generated in it by continuous electron-bombardment. The usual method is to mount the target material on a hollow copper tube through which cold water is continuously circulated. The target is made of a metal like tungsten or molybdenum having a high melting point and a high atomic number. Metals with high atomic number give more energetic and intense X-rays when used as targets.
In the time of X-rays production, majority percentage of incident power is converted into heat i.e more than 99%. Minority percentage of incident power is converted inro X-rays radiations i.e less than 1%.
In the Coolidge tube, the intensity and frequency of X-rays can be easily controlled.
The intensity of X-rays depends on the number of electrons striking the target per second. The number of electrons given out by the filament is proportional to its temperature, which can be adjusted by varying the current in the filament circuit. Therefore, the intensity of X-rays varies with the filament current.
The frequency of X-rays emitted depends on the voltage between the cathode and the anode(target). Let V be the accelerating potential across the tube, e be the charge on the electron then workdone on the electron in moving from the cathode to the anticathode= eV. The electron thus acquires Kinetic energy (K.E) which is converted into X-rays, when the electron strikes the target. If v(max) is the maximum frequency of the X-rays produced, then hv(max)= eV.
Therefore, the minimum wavelength produced by an X-ray tube= hc/eV.

Properties of X-rays:
a. X-rays are elecromagnetic waves.
b. X-rays are not deflected by fields (electric and magnetic).
c. They move along the straight path with the velocity of light in vacuum.
d. X-rays can cause photoelectric effect.
e. X-rays undergoes reflection, refraction, diffraction, interference and polarization.
f. They produce illumination of fluorescent materials on which they fall.
g. They ionize the gas through which they pass.
h. They can penetrate thin materials like wood, thin sheet etc.
i.  They donot pass through heavy metals and bones
j.  X-rays cast their shadow on the screen.
k. They affect photo-graphic plates.
l.  X-rays fall on the metal surface having high mass number, secondary X-rays are produced.

Semi-conductors

Semiconductor is a material which is neither a good conductor of electricity nor a good insulator. Simply, Those solid substance whose elecrical conductivity lies between good conductors and insulator are known as Semiconductors. Its conductivity lies midway between a conductor and an insulator. The resistivity of semiconductors varies from 10^-5 to 10^-4 ohm-m as compared to the values ranging from 10^-8 to 10^-6 ohm-m for conductor and 10^7 to 10^8 ohm-m for insulator.Examples of such substances are the crystalline forms of the fourth group of the periodic table. Germanium(Ge) and silicon(Si) are two very typical substances showing this behaviour.The band gap of semi-conductors varies from 0.2 to 2.5 eV which is quite small as compared to that of insulators. Eg: The band gap of diamond (a typical insulator) is 6 eV. The valence band and conduction bands of metals may even overlap.
At absolute zero temperature, a semiconductor behaves as an insulator because all the electrons are filled in its valence band and the conduction band is empty. But when the temperature increases the electrons starts to jump to the conduction band so that conductivity increases and resistivity decreases. Hence, the increase in temperature has negative coefficient of resistance in semi-conductor.

Currents in the Semiconductor:
There are two types of current in semiconductor which are classified as:
Electron current: The electric current which is set up in the semi-conductor due to the movement of free electrons in its conduction band is called electron current.
Hole current: The electric current which is set up in the semi-conductor due to the movement of the holes is called hole current. Its direction is opposite to the electron current.

Types of Semi-conductor:
There are two types of Semi-conductor:

Intrinsic semiconductor: The semiconductors like silicon (Si) and germanium (Ge) which are found in their pure state are called Intrinsic semiconductors or pure semiconducrors. In Intrinsic semiconductor the electric current is set up by thermally generated electrons and holes which is in very less amount and cannot be used significantly.
Now to increase the electrical conductivity of semiconductor other impurity atoms can be mixed with pure semiconductors. The process of mixing of impurity atoms with pure semiconductor atoms is called dopping and the impurity agent which is mixed is called dopping agent.

Extrinsic semiconductor: The semiconductors which are obtained by mixing with other impurity atoms in suitable amount with pure semiconductors are called Extrinsic semiconductors. Generally, one impurity atom is mixed with 8 pure atoms. Now the electrical conductivity of the semiconductor can be highly increased. On the basis of mixing of impurity atoms there are two types of extrinsic semiconductors which are listed below:

N-type extrinsic semiconductor: The extrinsic semiconductor which is obtained by mixing pentavalent impurity atom like As, P and antimony (Sb) then it is called N-type extrinsic semiconductor. It is called N-type because the majority charge carriers of such semi-conductors are free electrons.
Donor atom: In N-type semiconductor the pentavalent impurity atoms which are mixed to the semiconductor atoms donate an electron for the electrical conductivity, so these are called donor atoms. When they donate an electron, they are positively charged.

P-type extrinsic semiconductor: The extrinsic semiconductor which are formed due to the mixing of trivalent impurity atoms like boron (B), aluminium (Al), galium (Ga) etc with pure semi-conductor atoms are called P-type extrinsic semiconductor. Here P stands for positive. It means the majority charge carriers of P-type semiconductors are holes and minurity charge carriers are free electrons. Only the fraction of total current is obtained from free electrons.
Acceptor atom: When trivalent impurity atom is mixed with pure semiconductor atom, one bond is incomplete and creates a hole. This hole has a tendency to attract the free electrons i.e, it accepts the electrons. So, trivalent impurity atoms are called acceptor atoms.

Why Semiconductor is damaged by the strong current?
Ans: When strong current is passed through the semiconductor, it heats up the atoms in the covalent bonds of semiconductor. Now the covalent bonds are broken and the electrical conductivity of semiconductor increases. It means it loses the property of semiconductor and shows the behave of conductor. Hence, the semiconductor is damaged by the strong current.

Optical Instruments and Photometry

1. Defects of vision:

a.The least distance upto which an object can be clearly seen by a naked eye is called the least distance of distinct vision which is 25cm for normal eye.
b.The farthest point for the clear vision is infinity.
c.Ability of eye less to change its focal length is call power of accomodation.
d.When eye is relaxed it has maximum focal length and minimum focal length when eye is most strained(25cm).
e.The limit of resolution of eye is one minute.
f.The 355 resistance of vision of human eye is (1/10) sec.

1.1. Myopia (short sightedness):
In it distant object are not clearly visible. Image of the objects from before the retina. This defect can be removed by using spectacles having divergent lens. Suppose a person can see an object at maximum (x) then to see the distant object a divergent lens has to be introduced which has a virtual image of the object at a distance of x from the eye.
   i.e. u = Infinity
     V = f = -x
     Therefore, power of the lens, P = 1/f = -(1/x)

1.2. Hypermetropia (longsightedness):
In it near objects are not clearly visible. Image of the objects form behind the retina. This deftect can be removed by using spectacles having convergent lens.
i.e. u = D
    V = -d
   Or, 1/f = 1/u + 1/V
Therefore, 1/f = 1/D - 1/d.

1.3 Presbyopia:
In this defect both near and far objects are not clearly visible. This defect takes place at old age and is called old age defect. This defect is remedied by using bifocal lens. It is due to the loss in elasticity of ciliary muscles.

1.4. Astigmatism:
It is not equally clear in two mutually perpendicular directions which is due to the uneven curvature of the cornea. This defect is corrected by using a cylindrical lens.
     Visual angle: It is the angle subtended by an object at the eye . It is maximum when the object is at the least distance of distinct vision.
     i.e. visual angle = h/D

2. Microscope:
It is an optical instrument used to increase the visual angleof near objects which are too small to be seen by our naked eye. Microscope are of two types viz, simple microscope and compound microscope.

2.1. Simple Microscope:
It is also known as magnifying glass or magnifier and consists of a convex lens with object between its focus and optical centre. The image formed by it is errect, virtual, enlarged and on the same side of lens.

2.2. Compound Microscope:
It consists of two convex lens of short focal length, objective lens and eye piece. Object is outside the focus of objective which forms real image and acts as object for the eye piece. Depending on the adjustment, the image can be formed at the least distance of distinct vision or at the infinity.

3. Telescope:
It is an optical instrument used to increase the visual angle of distant objects. They are of three types:
3.1. Astronomical telescope: It consists of two convex lens, objective lens of large focal length and aperture and eye piece of small focal length and aperture. Object is at the infinity, so the image is formed at the focus of the objective lens which acts as the object for eye piece.

3.2. Terrestrial telescope: It is used to see distant object on the earth. The final image is virtual, errect and diminished.

3.3. Galilean Telescope: It is also a type of terrestrial telescope but of much smaller field of view. It's objective lens is a convergent lens while the eye piece lens is divergent lens. The final image is virtual, errect and diminished.

4. Photometry: 
The branch of optics which study and measure the light emitting capacity of a source and illuminance produced by it.

Radiant Flux (R):
The total energy radiated by a source per second is known as Radiant Flux (R). It's unit is watt.

Luminous Flux (Ø):
The light energy radiated by a source in one second is called Luminous Flux (Ø). It's unit is lumen.

Luminous intensity (I):
The luminous flux per unit solid angle is known as Luminous intensity (I). It's unit is candela i.e, lumen per steradian.

Illuminance (E):
The luminous flux per unit area falling normally is known as Illuminance.
It's unit is lumen/m² or lux.
Therefore, E = Ø/A = I/r² (For point source)
E = Ø/A = (4(pie)I) / 2(pie)rl = 2I/rl
Therefore, E is directly porportional to 1/r ( For a cylindrical source)

Lambert Cosine Law:
It states that " at a given point for a given source illuminance varies linearly with cosine of angle of incidence ". i.e E is directly porportional to cos(theta).

Photometer: 
It is a device use to compare illuminating power of two sources.
Two sources placed at a distance r1 and r2 form a screen having same illuminance then,
E1 = E2
or, I1/r1² = I2/r2²
or, I1 /I2 = ( r1 /r2 )²