Electrostatics-Introduction

*This article will give you a brief insight about the notion of charge and its effect on surrounding charges.*

Electrostatics is all about the interaction of charges with its neighboring charges which includes calculating the forces experienced or the energy of a system.This brings us to a basic question as to what is a charge?..Can we see it?..feel it?..

Like weight or mass in mechanics ,charge is a characteristic or a property of a body.We say that "this paper is very light"which implies we measure the lightness of the paper by saying its mass is less.Similarly charges have magnitudes.But unlike mass charges can be positive or negative.This is purely a convention.Electron the fundamental particle of matter is assumed to have a negative charge.Thus any excess of electrons on abody makes it negatively charged.And deficiency of electrons leads to a positive charge.

Analogous to the Law of gravitation in mechanics ,we have coulombs law in electrostatics which gives the magnitude of force between two bodies of charge Q1 and Q2

According to which F=K*Q1*Q2/r squared

k=1/4*pi*epselon not

epselon not=permittivity of free space

r=distance between the two charges

We would look into epselon and epselon not when we discuss about dielectrics in subsequent articles..

Electrostatic force obeys the principle of superposition which states that if F1,F2,F3...are the forces acting on a body independently ,then the net force acting on this body=F1+F2+F3+.....

QUESTION- 6 charges of magnitude q are placed at the corners of a regular hexagon,there is a charge with magnitude 2q at the centre.Now on of the charge from the vertex is removed.Find the force experienced by the 2q charge in this new configuration.

ELECTRIC FIELD -Loosely it is defined as the region around a charge in which the force due to it on any other charge is experienced.

CONCEPT OF TEST CHARGE-

THERE IS A CARTOON IN WHICH IN THE FIRST CASE A HAFTY MAN(A) IS PLAYING ARM WRESTLING WITH ANOTHER OF SIMILAR BUILT.IN THE SECOND CASE HE IS FIGHTING WITH A BOY WHO LOOKS MALNOURISHED.

Consider the above situation .Say we want to determine the strenght of A .In the first case,if he plays with Bwho looks equally strong ,we won't be able to know the actual power of A.Meaning,even if he wins,he would do that by a small margin.Whereas in the second case he would win by a huge margine.Similarly in electrostatics,if we want to determine the strenght of a charge,we should compare it with a charge who's magnitude is much much smaller than the actual charge.Such a charge is called the test charge.And the strength which we mean above is actually known as ELECTRIC FIELD INTENSITY.(or sometimes just electric field)

If we want to determine the Electric field of a point cahrge at a distance r from its location ,we place a test cahre pf amgnitude Q0 at r.Force on the test charge according to coulombs law is

F=K*Q*Q0/r squared

Electric field intensity is defined as E=F/Q0

E=K*Q/r suared (with proper direction)

ELECTRIC FIELD LINES

Instead of finding the magnitude of E,there is a nicer and simpler way of diagramatically solving such cases.

Electric field lines are the curves in space such that tangent to them at any point gives the direction of electric field at that point.

QUESTION AND COMMON MISCONCEPTION-Sometimes it is stated that Electric field lines are the paths traced by a charge in an elecric field..WHICH IS WRONG

I'll later give examples to disapprove this fact.

E also follows the superposition principle.Here are some figures showing electric field lines of point charge and an assembly.

TO BE FOLLOWED BY DIAGRAMS.

We see that

1-electric field lines originate from +ve charge and terminate on -ve charge

2-the arrow representing the electric field becomes shorter as one moves away from the charge.-this proves the inverse law nature of electric field

3-intensity of E is determined by the density of field lines

4-field lines never cross each other

Concept of Electric Potential

HERE IS A CARTOON SHOWING A PERSON CARRYING A BUCKET OF WATER TO THE TOP OF THE HILL.THERE IS A DIALOGUE IN WHICH HE SAYS THAT HE'S TOO TIRED CARRYING WATER.THE OTHER PERSON SAYS THAT-THIS BUCKET MUST HAVE GAINED A LOT OF POWER (ENERGY) AS IT HAS CONSUMED THE ENRGY OF THE FIRST PERSON.

We see that to carry the bucket from the bottom of the hill;work was done by the person holding it...work was done against the gravity at the expense of his mascular energy.Now, the bucket at the top of the hill has enrgy due to its configuration (position from the ground).We call it garvitational potential energy.

Analogous to gravitational potential energy ,we have electroststic potential energy due to a cahrged configuration.To find the electrostatic potential energy,consider a charge of magnitude Q placed at A.force experienced by a charge at distance r is given by 1,thus to move the charge (considered positive) towards A,one must apply equal force in the opposite direction.Say want to move this charge from r1 to r2.

work done by the moving agent =change in potential energy of the system= integrating F.dr

as r goes from r1 to r2.

say we bring the charge from infinity to a point r,

potential energy at infinity is=0

so we get U=K*Q*Q0/R

ELECTRIC POTENTIAL-is defined as the potential energy per unit charge .So, electric potential V=K*Q/R

-Alwin Jose