## Monday, 23 December 2013

### ELECTRIC CAPACITY

ELECTRIC   CAPACITY
IF the amount of water is added in any pot then the level of liquid in the container increases and water will be accumulated in the container up to  a certain level after wards it will  overflow.               similarly if change  is given to any conductor then it’ s  level of charging or say potential will increase . More the charge more the potential.
Thus we can conclude potential of any conductor and amount of change present on the conductor and proportional to each other. If we give  ‘Q’ change to any conductor and increase in it’s potential is V then
Q     V
Q =VC              Where,  C is the electric capacity of the conductor .  or Capacitance of the
conductor of the conductor

CAPACITY OF ANY CONDUCTOR   IS CONSTANT WHICH DEPENDS ON -->
(1)  Shape of the conductor                  (3) Medium around the conductor.
(2)  Area of the conductor.                   (4) Presence of any other conductor close to the charged conductor

Q=CV
(i)                                  C=Q/V
(ii)     If   V =Unit increase in potential

C=Q
DEFINITION OF ELECTRIC CAPACITY =>
Electric capacity of any conductor is the ratio of charge given to the conductor and increase in the potential of the conductor. OR .    Electric capacity of any conductor is numerically equal to the amount of charge required to increase its  potential by unit.

Definition of One   Farad =>If the increase in potential of any conductor is one volt due to the charge of one  coulomb then the capacity of the conductor will be one Farad .
CAPACITY OF ANY ISOLATED SPERICAL CONDUCTOR

Consider any spherical conductor having radius ‘R’ center ‘O’ and charge given will be uniformly distributed over the surface of the conductor so its surface will be equipotent surface and electric lines of force will be along the radius now potential on the conductor will be  V-

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Atmospheric electricity
The earth’s atmosphere extends to about 300 Km above the earth surface. The atmosphere is divided in four layers.
 300 km               400°C                                                                                     d4 = d/1010 Ionosphere                               Good Conductor 80 km               -90°C                                                                                     d3 = d/105 Mesosphere 50 Km               10°C                                                                                      d2 = d/1000 Stratosphere 12 km                -50°C                                                                                    d1 = d/10 Troposphere                             Poor Conductor                       Temp = 15°C                                              density of air d = 1.29kg/m3

Electrical properties of the atmosphere: -
(1)    The electrical phenomena in atmosphere take place between the earth surface and top of stratosphere. The 50 Km thick layers is like a blanket enveloping the earth.

(2)  An electric field 100 V/m is there downwards all over the earth, at ground level.

# Equation of state  for real gases or , Vander Waal’s gas equation for real gases:-

1. In the case of the ideal gases they obey gas equation       P x V =n RT
For the ideal gas we assume that volume occupied by the molecules of the gas is negligible is comparison to the volume occupied by the gas. But for real gas this condition will not by correct. Similarly, in the ideal gases, the real gas this force will not by negligible and that will effect the pressure exerted by need two corrections in the alone equation:  -
(i)Volume correction = In the ideal gas volume occupied by the molecules is negligible but in the real gas molecules will occupy some volume the then the volume for the motion molecules of gas will be-
V-b
Where b is a constant = 30 cm3/mole
(2)Pressure correction:-
1.    In the ideal gas the molecular force is supposed to be zero. If they is a molecular force existing between the molecular of real gas then the volume of pressure exerted will increase and it is given by -

# GRAVITATION

1.                              In The universe every mass attracts the other mass by a force, which is known as gravitational force.
2.                              Earth also attracts the other masses and the force of attraction of earth is said to be force of gravity.
Newton’s Law of Gravitation: -
This law is for the force of attraction between any two-point masses.
Consider two masses m1 & m2 , kept at a distance of  r  in between then the force acting between then will be   ‘F’ which is given as
<![endif]-->                             F                           F
m1                                                                  m2

r
1        The force of attraction is proportional to product of masses say
F
<![endif]--> m1 m2
2.   The force of attraction is inversely proportional to the square of distance between the masses. i.e.

3.    The gravitational force is always attractive force.

4.    The gravitational force will be along the line joining the masses.  So,

G  =  Gravitational Constant having same value in the complete universe.
G  =    6.67 x 10 –11  Nm2     kg –2                                                  [G]  =  [M-1 L3 T-2]
F   =    6.67 x 10 –11
Definition of unit mass or one kg   :-
If   m1 =  m2   =   1 kg ,       r  =   1 m
F = 6.67 x 10-11  Nm2 kg-2

It two equal masses are kept at a distance of –1m apart and force acting between them is 6.67 x 10-11 N, then each mass will be unit mass of 1 kg.

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SUBSTANCE / MATTER  -
It has mass and occupies space.

Substances have three types -
1.    Solid     -  Constant Volume & Fixed Shape.
2.    Liquid  -  Constant Volume & Shape according to pot or container.
3.    Gas       - Volume and  shape both are not constant depend on the pot or container.

Molecule : The smallest part of substance having all properties of substance and having free existence.

Atom : The smallest part of substance which is a unit in chemical reactions. It is not having free existence and properties of substance  (r = 10-10 )

Structure of Atom :
Nucleus : Central part of atom having radius 10-10 m.  Total mass and total positive charge of atom is concentrated in it or say protons and neutrons are present in it.

Orbital Electrons : Electrons is a  negativity  charged particles, the charge of electron is numerically equal to charge of proton.  The  total charge of orbital electrons is equal and opposite to the charge of protons present in nucleus. The electrons revolves around the  nucleus in different orbits.

Orbital electrons are divided in two parts - 1. Bound electrons, 2. Free electrons

Bound electrons : The electrons except outer most orbit are said to be bound electrons. They are tightly bound with nucleus or they feel strong force due to nucleus so they can not leave atom.

Free electrons : The electrons of outer most orbit are said to be free electrons. They are said to be free because they feel least force or binding due to nucleus. They can leave atom by getting small amount of energy by any means.
Free electrons decide the electrical and thermal conductivity of the substances.

The minimum amount of energy required by any free electron to leave atom is said to be ionization energy of atom. The energy is different in different substances.

The binding of nucleus on free electrons is different in different substances.

The minimum amount of energy required in taking out any free electron from any substance is said to be work function.

The work function of different substances is different. It is minimum for alkaline metals (Na, K) and maximum for hard metals.

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Electric Potential

1. When any charge or charged body is kept in free space or in any medium there will be an electric field around the charge or charged body.
2. The electric field produced by charged body is measured by two quantities –
a)      Intensity of electric field
b)      Potential of electric field
1. The intensity of electric field at any point is the force per unit charge kept at the point in the electric field. The value of intensity of electric field is given by –
2. The potential of electric field at any point is the work done per unit charge in carrying the testing charge from out side the field to the point in side the field.

This is the potential at any point due to the charge or charged body. The value of
electric potential at any point due to charged body is given by –

1. If any body is charged some amount of work is to be done in this process of charging. The work done is related with the potential of the charged body.

We can define the potential of charged body as –
The degree of charging of the body is said to be the potential of charged body.
OR
The potential of the charged body is the property of the charged body which decides the
direction and rate of flow of charge between the charged bodies kept in contact.

The positive charge will flow from higher potential to lower potential and   negative
charge will flow lower potential to higher potential.

The electric lines of force will be from higher potential to lower potential.

1. The potential of the charged body is related with the electric capacity of the charged body. The relation between capacity and potential of the charged body is given by –

q = Amount of charge on the body.
V = Potential of the charged body.

C = Electric capacity of the body.