conversion of galvonometer into ammeter and voltmeter

This video gives complete explanation about how to convert galvonometer into ammeter and voltmeter

principle of shunt resistance

Shunt resistance should be connected in the circuit to save the galvonometer from very large currents and it is connected to moving coil galvonometer in parallel manner.

moving coil galvonometer

Moving coil galvonometer depends upon the principle that  a current carrying coil rotated itself when placed in a magnetic field. In this galvonometer, the deflection torque and restoring torque are equal

Force and Torque on a current loop in a magnetic field

This video tells about the effect of magnetic field when a current loop placed in a strong magnetic field and also explains about torque which acts as a deflecting torque on the current loop.

Fleming's Left hand Rule

This video explains about Fleming's Left hand Rule.

Force between two parallel conductors carrying current

• Ampere showed that two parallel conductors carrying currents in the same direction have attractive force between them and carrying currents in opposite direction have repulsive force.

Biot-Savart law

This video explains about the Biot-Savart law remaining part of previous session.

Ampere's law and Biot-Savart law

• Ampere showed that if a continuous closed line or loop can be drawn round the current carrying conductors or conductor  and B is the magnetic induction in the direction of an element dl of the loop, then line integral of  B.dl=Uoi
• Biot-Savart law is applied for the curved current carrying conductor, on the other hand Ampere's law is applied for the uniform current carrying conductor.

     

Introduction to electromagnetics

In this video, i have discussed about the fundamental of electromagntetics and rules for the relation between the current and magnetism

Thomson effect and its explanation

• Thomson effect is improvised effect on Peltier effect.
• When current flows through thermo couple, then heat energy is evolved or absorbed not only at junctions, but it is absorbed or evolved  all along one or both the conductors.
• Thomson coefficient is nothing but the heat energy is evolved or absorbed  when a current of 1A flows for one second between two points of a conductor which differ in temperature of one degree centigrade.

Peltier effect and its explanation

• Peltier effect is converse of Seebeck effect.
• When a current is passed across the junctions of two dissimilar metals, then heat is evolved at one junction and heat is absorbed at another junction. This effect is called Peltier effect.
• Peltier effect is reversible where as Joule's heat effect is irreversible
• The amount of heat evolved or absorbed at junctions is called Peltier coefficient.

Thermo galvonometer and its explanation

This video tells about how the thermo galvonometer and it works and on what principle it depends

Thermo electricity and seebeck effect

•  According to Joule's law, the current passing through a resistor produces heat
• Seebeck is a scientist who discovered that heat energy can be converted into electric energy
• Seebeck  discovered that when two dissimilar metals  are joined to form a closed circuit with junctions and if the junctions are kept at different temperatures an emf is generated and current flows through the circuit.

steady current and its topics

• Flow of charge of current per unit time is called current
• Convenction current direction is always opposite to the direction of flow of electrons
• Current density is defined as the ratio of the current to the cross section area
• When the electric field is established between the two ends of the conductor, the free electrons experience a force. The motion of the electrons get accelerated, but the speed of the electrons does not increase continuously. The electrons in the conductor collide and collide again with positive ions of the conductor such that they lose the energy which appear in the form of heat. Altogether this field does not give any acceleration to the motion of the electrons such that constant velocity of electrons is maintained. That constant velocity is called drift velocity.

Problems on coulomb's law

This video indicates  two problems on coloumb's law

effect of dielectric on energy stored in a capacitor and its explanation

This video indicates the effect of dielectric on energy stored in a capacitor when the circuit connected to charging battery and when the circuit is disconnected from the charging battery

Energy stored in a capacitor and its explanation

This video explains about the energy stored in a capacitor.

Combination of capacitors and its explanation

This video has explanation about series and parallel combination of capacitors

Dielectric materials and its explanation

This video explains about non-polar dielectric materials and polar dielectric materials and the effect of dielectric on the capacitor

Funny Fysics...hehehe...

Dielectrics and its explanation

This video is taken from windows movie maker through www.youtube.com

Capacitor and its explanation

This video is taken with the help of windows movie maker through www.youtube.com

The relation between the electric field and potential difference

This video is taken from windows movie maker with aid of www.youtube.com

Electric potential at a point due to point charge

This video is taken with help of windows movie maker  and with aid of  www.youtube.com

electric field at a point on the perpendicular bisector of an electric dipole

This video is taken with help of windows movie maker and with aid of www.youtube.com

Electric field due to an electric dipole

The electric dipole is made up of two equal and opposite charges +q and -q coulomb seperated by a distance 2l metre as shown in the below figure
In order to calculate the electric field at a point P distance r from the centre O of the dipole. Let  E1 and E2 be the intensities of electric field at P due to +q and -q respectively, So

Then the resultant intensity at point P will be different of the two intensities because they are along the same line but in opposite directions. Thus

E=E1-E2(Since E1>E2 in direction of AP)

Motion of the centre of mass of earth-moon system

The moon moves around the sun in circular orbit and the earth moves around the sun in an elliptical orbit. Comparing of mass of earth is far greater than the mass of the moon such that the gravitational force between the earth and the moon treated as internal forces for the earth-moon system. But earth-sun system, it is quite opposite and the gravitational force between the sun and the earth-moon system is treated as external force such that the motion of the centre of mass of the earth-moon system is in elliptical path around the sun. Suppose a stationary body explodes in different fragments with velocities v1 and v2 in different directions, then
(v1/v2)=(m2/m1)

Explosion-centre of mass

Imagine a shell is fired making certain angle with horizontal direction. It is under the influence of gravitational force and allows the parabolic path. Let the shell explodes into fragments due to internal forces in its path. It will be found that different fragments will fly in different directions. But only one point in the system does not disturb its path, i.e., it follows in parabolic path. In the process of explosion, some changes may occur in momentum of individual fragments due to internal forces, but the centre of mass has its motion unaltered. From this once again it can be proved that centre of mass  solely depends on external force, but gravitational force is applied on the shell from the beginning which continues the motion of the shell in parabolic patThis figure shows the path of the shell under explosion as a parabolic path.

Intensity of electric field due to a point charge

This video gives the explanation about intensity of electric field due to point charge and it was taken with aid of windows movie maker and www.youtube.com

Electric lines of force and its explanation

This video tells about the concept of electric lines for force. This video is made using windows movie maker from where it is uploaded to www.youtube.com from which it is taken to www.narasimhakanduri.blogspot.com

Coloumb's law and its explanation

This video gives fundamental knowledge about the force between charges and this video is taken by using windows movie maker  and uploaded to www.youtube.com

Electrostatics and its brief introduction

This video is recorded using web cam and microphone through the aid of windows movie maker via www.youtube.com

Electrostatics-video

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This video indicates some slide show of electrostatics topics which are taken via www.youtube.com with aid of windows movie maker.

centre of gravity and its applications

centre of gravity concept is widely applicable in day to day life. We often listen mostly lorry accidents occured. Can you imagine why that is happened? because centre of gravity is greater height comparing with other vehicles. Even centre of gravity is applicable for us also, how? if we stand on the floor because of our centre of gravity is stable and in balancing position. The roads at turnings are constructed with making some angle by one side of the road with the earth to overcome the accidents made by vehicles. Due to this reason, vehicles maintain centre of gravity  balanced. When the man is walking on a rope holding a pole in his hand is possible by balancing his centre of gravity is stable.

Coordinates of centre of mass

Let us consider a system of  two particles m1 and m2 and placed at A and B having position coordinates x1 and x2 respectively from the origin as shown in above figure. If  Xcm is position coordinate of the centre of mass from origin
              Then d1=Xcm-x1
                       d2=x2-Xcm
                       d=x2-x1
         According to the definition of the centre of mass of the particles, if the centre of mass is defined  at C along AB  such that 
       product of (m1,AC)= product of (m2,CB)
       product of (m1,d1)= product of (m2,d2)
                Then
                   m1(Xcm-x1)=m2(x2-Xcm)
                    Xcm(m1+m2)=m1x1+m2x2
                     Xcm=(m1x1+m2x2)/(m1+m2)
        This is the position coordinate of the centre of mass.
From the above equation, the position coordinate is analog to the weighted mean displacement, i.e., where weighting factor for each particle is the fraction of the total mass that each particle has.
               Suppose, x1=0 and x2=d, then
                     Xcm=m2d/(m1+m2). This is the result when the origin is shifted to x1
               Suppose, x2=0 and x1=d, then
                          Xcm=m1d/(m1+m2). This is the result when the origin is shifted to x2
            If the origin is shifted to centre of mass i.e., Xcm=0 then x1=-d1 and x2=d2 then  
                    0=(-m1d1+m2d2)/(m1+m2) or m1d1=m2d2
                        Therefore, (d1/d2)=(m2/m1)
                 So, we can say that the ratio of the distances of centre of  mass  from masses is inverse ratio of their masses. We can say that the centre of mass is nearer to the heavier mass. The location of the centre of mass is independent of  the reference frame used to locate it. The centre of mass depends upon the masses the particles and the position of the particles relative to one another.

Stability and its applications

Mainly, the stability of a body depends upon the base  area  and height of centre of gravity for a body. Stability of a body increases with base area and decreases with the height of centre of gravity.
                There are three types of equilbrium for a body i.e.,
Stable equilbrium:-   A body is in stable equilbrium when its position is not disturbed.
Unstable equilbrium:- A body is in unstable equilbrium , if it does not regain its original position after it is being slightly disturbed
Neutral equilbrium:- A body is in neutral equilbrium if it changes its position without change in equilbrium after being disturbed.
          The stability principle is mainly used in constructing ship. For that purpose, the base of the ship  is made as large as possible and the height of the centre of gravity is made as small as possible to maintain the stability of the ship very high. Due to this reason, even the ship tilts a side but it regains its original position so that the ship is in stable equilbrium.
          Another application of stability is person walking  on a rope. When a person is walking on a rope by holding a long pole in his hand, he changes  the orientation of the pole  such that the line of action of the total weight passes through the rope  so that he does not fall down.

Difference between the centre of mass and centre of gravity

Consider a body consisting of large number of particles each of mass 'm' and each particle is attracted by the earth towards its centre with weight of  'mg'. Like this, the weight of  various particles constitute a system of  like parallel forces. The resultant of these forces are passing through a point in the body. That point is called the centre of gravity of the body.
               Therefore the centre of gravity of a body  is the point through which the weight of the body acts.
In case of small bodies, the centre of gravity and centre of mass almost coincide. Suppose if the body is large and so extensive that the acceleration due to gravity changes from one point to another point in the space occupied by the body where centre of gravity and centre of mass are different.
               The main difference between the centre of gravity and centre of mass is that centre of gravity depends upon acceleration due to gravity on different particles of the body, on other hand, centre of mass is independent of acceleration due to gravity.
                Centre of gravity is defined as the stability of the body when supported, on the other hand, centre of mass is defined to describe the motion of the body as a whole.

Centre of mass and its introduction

There are two motions for a rigid body i.e., rotatory motion and translatory motion.  When a wheel moves on a horizontal plane, it rotates moves on a straight line path. If a particle on the rim of the wheel is considered, it will have a complicated path. But the particle at the axis of rotation is considered, then it has straight line motion. Suppose  a  ball is moved in spinning manner, then any particle on the surface having complicated path of motion. But the particle at the centre of the ball moves in a parabolic path.
            From the above examples, we come to the conclusion that when a rigid body has both rotatory and translatory motions, the different particles on the body moves in different directions. But the particle at a specific point is moved along a particular direction and the body moves as if the whole external force  is acting on it and represents the motion of the entire body.
           The location of centre mass is determined as a fixed point of a system of particles or a rigid body within the boundaries of the system, where the entire mass of the system or body is supposed to be concentrated.
            For a uniform rod, the centre of mass is the middle point of the rod. For a rectangular plate, the centre of mass is intersecting point of thediagonals of the rectangular plate. For a circular plate, the centre of mass is at the centre of the circular plate. For a ring, the centre of mass is not within the body, but within the boundaries of the system
               So far we discussed about the motion of a rigid body, but in general, we have to deal with the system of bodies consisting of  large number of particles which have mutual interactions such that they may change the positions with respect to each other in a complicated way during the motion. Such system is called Non-rigid body system. Planets moving around the sun and each planet having satellites moving around them is an example of Non-rigid system..

Kirchoff's first and second laws

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emf of the cell

In order to maintain continuous flow of current through a conductor AB of resistance R, we should always keep A at a positive(higher) potential and B at a negative(lower) potential. We connect A to positive terminal P of the cell and B to negative terminal Q of the cell. Through chemical reaction, the cell always maintains P at a constant positive potential and Q at a constant negative potential.

In external circuit, current(+ve charge) flows from P to Q via the conductor AB. But, inside the cell the same positive charge moves from lower potential to higher potential. To do this, the cell must be able to do work on the charge. The energy to do this work is derived from the chemical process inside the cell.

The influence that makes charge move from lower potential to higher potential is called the electromotive force and is denoted by E.

The emf of a cell is defined as the work done in carrying a unit positive charge through the complete circuit including the charge flow inside the cell.

The emf is measured in the units of Joule/Coloumb or Volt. Thus emf has the same units as the units of potential difference.

The resistance to flow of current inside the electrolyte solution of the cell is called internal resistance of the cell. The emf and internal resistance of the cell will be fairly constant only when small current is drawn from the cell.

Thermistor and its applications

Thermistor is widely used in measuring the rate of energy flow in micro wave beams. The beams fall on a thermistor and heats it. A relatively small rise in temperature results in a very large change in resistance because, for a thermistor alpha is very high. By measuring the change in resistance, we can accurately measure micro wave power.

In a radio circuit, there will be several heater elements in series. A sudden change in the current through the circuit will damage the device. To prevent such a sudden surge of current, we place a thermistor with a high negative temperature coefficient of resistance, in series in the circuit. Initially, the thermistor is at cold state and hence has a very high resistance. This prevents the current to moderate level. Later, as the thermistor gets heated, its resistance decreases and it allows normal flow of current through the heater elements there by preventing surge. A thermistor can also be used as a thermostat.

Thermistor

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Temperature Dependence of Resistivity

The resistivity of the metallic conductors is found to increase with temperature. Over a limited range of temperature, the resistivity of metallic conductors is found to increase linearly (i.e., approximately) with temperature.


Thus, the temperature coefficient of resistivity may be defined as fractional change in resistivity per unit rise in temperature.

Above graph shows that variation of resistivity of a ohmic conductor with temperature(in kelvin)
Some important details about temperature dependence of resistivity as follows
a) For certain metals at lower temperature, the temperature dependence of resistivity is quite non-linear. The graph will be curve.
b)Metallic alloys like Nichrome have high resistivity. Therefore, it is used widely in electric heaters.
c)Resistivity of manganin and constantan is nearly independent of temperature. So, manganin is widely used in making resistance boxes, standard resistances and wires used in metre bridge and potentiometer.
d) The resistivity of carbon decreases with increase of temperature and has a negative temperature coefficient of resistance. Semiconductors like germanium and silicon, also behave in the same way.

conductance and conductivity

Conductance is defined as the reciprocal of resistance of a conductor, i.e., the ratio of the current i and voltage V.

Specific resistance or resistivity

In order to understand the behaviour of the materials, it is necessary to study certain properties like (a) Resistivity (b) Conductivity and (c) conductance.

The resistance (R) of a conductor depends on its length, area of cross section.

In the above equation if l=1m and A=1sq.m, then p(rou)=R. There is the difference between the resistance and resistivity i.e., resistance is the bulky property of a material and resistivity is specific property of the material.Since, specific resistance is proportionality constant, so that it is independent of length and area of cross section for that material.

For conductors, the specific resistivity like follows


From the above figure we found that for mercury, the resistivity is high.
For semi conductors, insulators resistivities like follows

From the above the above tables, we see that resistivity of insulators is about 10power22 times the metallic conductors. Since metals like silver, copper and aluminium have lowest resistivities, so that there are used in manufacture electric cables, connecting wires etc.

graphical properties of non-ohmic resistances

This figure shows that the relation between the current i and v in case of vaccum tubes i.e., an electronic device
This figure shows the V-i characterstics of a P-N junction diode rectifier which shows that non-linear relation between the voltage and the current in positive direction and in the reverse direction. This figure shows increase in the current is not possible beyond zeroth value of the voltage, so that either in positive value of V or negative value of V, for large value of the voltage, there is increase in the current.
This figure shows that the V-i characterstics of thermistor. The detail study of thermistor we can see in electronics subject.

Ohmic and Non-ohmic resistances(devices)

Resistances that obey the Ohm's law are called ohmic resistances. A metallic conductor at a constant temperature is called Ohmic resistance. For such ohmic resistances, the V-I characterstic curve will be a straight line passing through the origin.
In ohmic resistance, current is reversed in the direction when the potential difference is reversed, but the magnitude of the current remain the same.

There are many resistances that do not obey the Ohm's law. These are called Non-ohmic resistances. For these resistances, the V-I characterstic curve will not be linear. The function of modern electronic devices that do not obey the Ohm's law.

Ohm's law

Generally, for a metallic conductor has a constant resistance R when other physical conditions remain same. For a metallic conductor the current passing through conductor will be directly proportional to the potential difference V applied across its ends. George Simon Ohm gave the relationship between V and i, which is called ohm's law.
Ohm's law is just a empirical relationship. It is not a fundamental physical principle and does not specify any general property of matter. For electrolytes, another essential condition required for application of Ohm's law is that the physical state must remain the same. Ohm's law is valid only for metallic conductors in which V/i has a constant value irrespective of the magnitudes of V and i

Resistance and units

The resistance is defined as the ratio of the potential difference 'V' across it to the current 'i' which flows through the conductor.

Resistance (R)=V/i

When we apply a potential difference 'V' between the ends of a conductor, an electric field 'E' will be set up inside the conductor and as a result a current 'i' flows through the conductor. This causes root notion for the resistance.
Resistance is a characteristic of the conductor as a whole. Resistance depends in general on nature of material, its dimensions(length,area of cross section), its temperature.

In some type of conductors the resistance 'R' increases when 'V' is increased. In another type of conductors the resistance 'R' decreases when 'V' is decreased. In some type of conductors 'R' depends on the direction of current flows through it.

current and units

Current is defined as the rate of flow of charge through any cross section of a conductor. Electric current is defined as the net charge passing through any cross section per unit time.
Suppose the net charge 'q' passes through any cross section of the conductor in time 't', then the current 'i' is given by

i=q/t

Where 'q' is in coloumbs and 't' is in seconds and then 'i' is in coloumb/sec or ampere. Like the mass, current is macroscopic quantity in SI system and is dimensionally denoted as I or A

Current electricity

Generally, the free electrons are responsible for the flow of electric current. In a metallic conductor, on an average there will be one free electron available per atom. At any temperature, these free electrons move freely and collide with fixed atoms or ions inside the conductor. These collisions are inelastic in nature and causes the transfer of energy. The resultant velocity will be zero in any direction. But when potential difference is applied between the ends of a conductor, an electric field E will act on these free electrons. As a result, and electron moves with an average velocity in a direction opposite to the field. This is called drift velocity 'Vd' and is of the order of 10^-3m/s. Like that, all electrons will drift in the same direction. This drift is responsible for the flow of charge through the conductor. By convection, the direction of the current is the direction of positive charge motion.

In electrolytes or in gaseous conductors, the charge carries will be either positive or negative ions or both. But in case of semi conductors, the conduction is due to electrons and holes.

Electrolyte-capacitors

An electrolyte capacitor is obtained by passing a direct current between two sheets of aluminium foils
with a suitable electrolyte like aluminium borate between the foils. Due to electrolysis, a very thin film of thickness of the order of 10^-6cm of aluminium oxide is formed on the anode plate and acts as the dielectric between the plates. This oxide layer is very thin, so that capacity of this capacitor becomes very high. Care must be taken to connect this capacitor with proper polarity in a circuit. Otherwise the oxide film will break down. For this reason, in an electrolyte capacitor the polarity of terminals will be indicated.
These capacitors are widely used when high capacitances are required.

paper capacitor

Above figure shows that paper capacitor. In this, a paper soaked in oil or wax is used as the dielectric in between the tin foils that serve as a parallel plates. In order to increase the capacitance to large extent, several number of tin foils and wax papers to be used by arranging alternatively as shown in figure.
This entire capacitor can be rolled and sealed in a cylinder. Since, these capacitors occupy small space and are cheaper in cost and they are widely used in radio circuits and in laboratories.

multiple capacitor

Above figure shows that multiple capacitor which is a parallel combination of several parallel plate capacitors and is of fixed capacitance. Mica is used as dielectric which has dielectric constant 6 between a number of tin foils arranged in parallel.
If the capacitance between two successive plates is C, then the capacitance of the multiple capacitor is nC, where n is the number of dielectric plates used. This whole arrangement is sealed in a plastic case. These capacitors are used in high frequency oscillating circuits. Since, mica's dielectric constant does not change with temperature, so these capacitors are used as standard capacitors in the laboratory.

The above figure shows the variable capacitor which can be varied gradually. This is achieved by varying effective area between the plates. These plates are usually made up of brass or aluminium and semi circular shape. This capacitor consists of two sets of plates. One set of plates is fixed in position and is called the stator. The other set of plates can be rotated over the stator by rotating the piston. This set called rotor. During the rotation of the rotor, the area common to the plates of stator and rotor is varied.

Energy stored in a capacitor

Series combination of capacitors

The series combination of capacitors is shown in the following figure

From the figure, V1=Q/C1;
V2=Q/C2;
V3=Q/C3;
The potential difference across the series combination as
V=V1+V2+V3;
V=(Q/C1)+(Q/C2)+(Q/C3);
=Q(1/C1 + 1/C2 + 1/C3)
If C is the equivalent or effective capacitance of the series combination, and has the same charge Q, then C=Q/V and V=Q/C;
From the above equations,
Q/C =Q(1/C1 +1/C2 + 1/C3)
1/C=1/C1 +1/C2 +1/C3)
For 'n' number of capacitors,
1/C= 1/C1 +1/C2+.........+ 1/Cn
For two capacitors, the effective capacitance is
C=(C1C2 /C1+C2 )

Effect of dielectric on the capacitance of a capacitor

For a parallel plate capacitor,

Dielectric made of polar molecules

Dielectrics such as water, hydrogenchloride and alcohol made of molecules that have non uniform distribution of electric charges. In such materials, molecules in which the positive charge centre will not coincide with the centre of the negative charge, even in the absence of electric field. This shown in the following figure.
In the absence of external electric field, these molecules shows the polar characterstic, therefore when these molecules placed in an external electric field, the field will try to orient the positive charge centres in the direction of the field and negative charge centres in the opposite direction.
When polar molecules placed between the plates of a charged capacitor, the effect will be similar to that of non-polar molecules, the effect will be more pronounced because the molecules are already polarized even without field. The capacitance will increase C=KCo

Dielectric materials

Any materials that do not allow the electric charges to easily pass through the materials is called insulator or dielectric material.
Any material is made up of molecules but the molecules have symmetric charge distributions. So, such kind of molecules are called non-polar molecules. In the absence of external electric field, non-polar molecule has its centre of positive charge conincides with the centre of negative charge.
But, when the dielectric placed in an external electric field Eo, in each molecule the centre of positive charge will be displaced in the direction of the field, and the centre of negative charge will be displaced in the opposite direction. We called it as molecule gets polarized.



In the electric field Eo existing between the plates, each molecule in the dielectric gets polarized. Therefore, the entire dielectric gets polarized. Due to this reason, there become opposite charges to the charges on molecules of dielectric are induced. Inside the volume of the dielectric, the near by positive and negative charges cancel each other. Altogether, dielectric becomes neutral. Due to induced charges on the surface of the dielectric, the electric field Ei appears in the opposite direction to the actual electric field direction Eo.

So that, the net electric field E=Eo-Ei. Therefore, the potential difference Vo(without dielectric) reduces to V(with dielectric)

E=Eo/K
V=Vo/K
The capacitance of the capacitor with dielectric will be

C=Q/V=Q/(Vo/K)=K(Q/Vo)=KCo

Parallel Plate capacitor; Formula for capacitance

A parallel plate capacitor is a simple type capacitor in which parallel plates of area A are separated by a distance 'd'. The plates are any shape of square, rectangular or circular. If 'd' is very small compared with the area of 'A', the electric field between the plates will be uniform as shown by equidistant parallel lines of force. However, the field will not uniform at the outer edges of the plates. This shown by curved lines of force in figure. This is called 'fringing' and can be neglected when d<A.

When there is no material in between the plates, air fills the space and acts as dielectric with air as the dielectric, the capacitance of the parallel plate capacitor in terms of plate area(A), distance between the plates 'd' is given by

Principle of superposition

When there are more than two charges, we use this principle of superposition to get the effective force experienced by the a single charge due to presence of all the remaining charges.

According to the principle of superposition, the total effective force exerted on a given charge is the vector sum of all the individual forces that various charges exert seperately on the given charge

Let us consider charges q1,q2,q3..........qn kept stationary at different points. Let the force exerted on q1 by q2 is F12 the force assumed to be independent of other charges(in calculating the F12 we neglect the presence of all other charges excepting q1 and q2)

Similarly let the force exerted on q1 by q3 is F13..........and force on q1 by qn is F1n

Then the total effective force on q1 is given by
F=F12+F13+F14+.......+F1n

The force F12 can be directly calculated by Coulomb's law.

Effect of dielectric on force between charges

Dielectric constants of a medium

Dielectric constant is defined for medium as the ratio of permittivity of the medium to the permittivity of free space

The dielectric constant is also called the relative permittivity of the medium. Where permittivity is physical significance to permit the charge flow in a medium
Dielectric constant will be different for different materials and also it depends upon the temperature and pressure. Dielectric constant for the same material will be different for AC current and DC current. Dielectric constant varies according to the frequency in case of AC current.

Principle of a capacitor

A capacitor is a device to store charges and electrostatic energy. In the simplest form, a capacitor consists of two parallel metal plates separated by a layer of air or a dielectric.
Above figure shows that two parallel plates in which one plate A having positive charge which induces negative charge on other plate B, then the equal amount of positive charge on outside of plate B. The induced charge on the plate B gets neutralized due to earthing. While the induced negative charge on inner side of B is held in position by the attraction of positive charge on A. As this negative charge on B lowers the potential of A.
The principle of a capacitor is to increase the capacitance of a conductor by bringing an uncharged conductor near to it and earthing the outside of the uncharged conductor.
C

Capacitance and its physical significance

Generally, capacity tells about the ability of strength of particular one. When we come to electrostatics in which the capacitance has the meaning but here is what is the quantity denotes about the capacity is that the charge ability of particular device.
Like different containers have difference capacities to fill the liquid, different conductors have the difference capacities to hold the charge. The capacity of a conductor to hold the charge is called
capacitance which is analogous to the volume of container to fill the liquid. Capacitance of a conductor depends on the size, shape and surroundings of the conductor.
In case of isolated conductor, when the charge on the conductor is gradually increases, then its potential will also be increased gradually. Therefore, the charge on the conductor is proportional to the potential.

Relation between the electric field strength and potential difference

From above figure, we have to find out the relation between the electric field strength and the potential difference. There are two points A and B with a distance of 'd' between them.

Electron volt and its significance

Electron volt is the energy acquired by an electron to accelerated through a potential difference of one volt

Magnitude of electron charge e=1.6*10^-19, accelerating potential difference V=1volt
Then the energy acquired by an electron when accelerated through 1 volt P.D. is
W=qV
=1.6*10^-19*1J and is called one electron volt(eV)
To convert the joule to electron volt, one has to divide the value in joul by charge of electron.
The energy levels and ionization energies of atoms and binding energies of molecules are usually expressed in electron volts.
The eV is too small a unit for expressing energies in nuclear physics.

Potential energy of a system of two charges

Let us place positive charge q1 at A, then there is no need to work to place the charge q1 at A because there is no electric field at A. Now, there is electric field around q1. Let us now bring another positive charge q2 from infinity and place it at B at a distance r12 from the charge q1.

Electric potential due to point charge

In order to find out electrical potential due to point charge, first we consider an isolated point charge 'q' at O. Therefore, the charge produces an electric field around it. We have to find out the electrical potential at a point P at a distance r from the charge. The electric field direction is along OP. Now, let us consider a point A at a distance 'x' from O on the same line OP

Potential difference-its meaning

We have already known potential is the workdone to take the test charge from infinite distance to a point against the electric field.
But potential difference is the workdone by the test charge in taking from one point to another point against the electric field

One point here to remember that the field produced by a positive charge is always directed away from the charge, so we need to do work and hence the potential at any point around the positive charge is positive.

Electrical potential-definition

The electric potential at a point in an electric field is defined as the work done in bringing a unit positive charge from infinity distance to that point against the electric field.
Here we consider that the electric field of the charge and at an infinite distance from it, field strength is zero because the electric potential is more than field strength produced by the charge at infinity.
If an amount of workdone W is done in bringing a test charge q from an infinity to a point against the electric field, then the potential at that point is given by
V=W/q

Electric potential-significance

potentiality means strength, so electric potential means it tells about electric field strength.
Earth is a huge reservoir of charges and hence adding or removing of charges from the earth, there is no change occurs in its potential.
Now let us consider a positively charged body to be connected to the earth by a conducting wire, then it has less number of electrons than usually required. Hence, there is flow of electrons from the earth to the positively charged body. Therefore, conventional current flows from the body to the earth.
Now let us consider a negatively charged body to be connected to the earth by a conducting wire, then it has excessive electrons than usually required. Hence, there is flow of electrons from the body to the earth. Therefore, conventional current flows from the earth to the negatively charged body.
From above two cases, whenever the body gets its required charges, then it becomes neutral charged, i.e., there is no flow of electrons to outside or inside.
So, we say that electrical potential is physical quantity which tells about the field strength i.e., either positive charged or negative charged.

Intensity of electric field due to a point charge

A point charge 'q' is placed stationary at O in air. Place a test charge qo at P. From Coulomb's law, the force experienced by 'qo' is given by

Electric lines of force

To visualize the electric field, Farad introduced the concept of electric lines force. There is a margin between electric field and magnetic field that in magnetic field the lines of force are not end up but in case of electric field that is different i.e., electric lines of force are end up at the poles.

Travelling of passing positive charge along a imaginary curve taken to be the electric line of force. One of the important point to remember that the tangent to the curve at any point will be parallel to the direction of electric field strength at that point.

In a uniform electric field the lines of force are equidistant, parallel and straight lines.

Here are some important points about the electric lines of force as below
1. Electric lines of force always normal to the surface of a conductor.
2. All electric lines of force diverge out from a positive charge and they converge in to a negative charge
3. No two electric lines of force intersect each other. If they intersect at any point, at that point the electric field should have two different directions, which is not possible. The same principle occurs in case of magnetic field
4. Electric lines of force denotes the field strength is strong when lines of force crowded and sparse where the field strength is weak.
5. Electric lines of force are only imaginary lines, but it could not have physical existence.
Some are the important figures tell about the electric lines of force as below

Electric field-intensity of electric field

Electric field is nothing but the space around an electric charge where the electric force due to charge is felt by another charge.
The intensity of electric field or Electric field strength at a point in space is defined as the force experienced by unit positive charge placed at that point.
Suppose we place a test charge q at the point and the force experienced by it is F, then
field strength E=F/q, from it we can obtain the force on the charge F=Eq, here q is test charge taken to be infinitesimally small and positive because we have to take unit positive charge actually, but it is not possible, so that we take like that, unit positive charge is ideal thing.
If the electric field intensity is same in both magnitude and direction at every point of the field, then that electric field is uniform electric field.
If the electric field intensity changes from point to point of the electric field either in magnitude or in direction or in both then that electric field is called non-uniform electric field

resemblance of coulomb's law and gravitational law

Coulomb's law tells about the electrosatic force between two charges, on other hand gravitational law tells about the gravitational force between any two masses.
The electrosatic force is either attractive or repulsive depending on the charges(positive, negative)

From above, the value of K is more and more than the value of G.
From this, we can conclude that the value of electrostatic force is greater than gravitational force. Due to this reason, in nature, even every substance is made up of atoms contains electrons, protons(which causes electricity), electrostatic force does not occur because they uncharged, so that we can gravitational force occurs between them. So, they are fix up to the earth.