Electrostatics
what is electrostatics ?
It is a branch of physics in which we study about static charge i.e charge at rest .
Electrostatics is made up of two word
Electro + statics
Electro means charge and statics means rest .
what is an electric charge ?
- Electric charge is a basic property of matter which causes force when it is placed in the electromagnetic field .In simple way we can say that only electric charge is responsible for the electric forces.
- It's s.i. unit is coulomb (c)
- It's formula ; Q = i*t
what are the properties of charges ?
There are following properties of charge -:
1. charge is Additive (scalar)
2 charge is invariate( not vary with velocity)
3. charge is conserved (constant) .
4. charge is quantise.
charge is conserve
A/c to charge conservation total charge of an isolated system remains constant.
i.e charge can neither be created nor destroyed.
Initial Amount of charge = final Amount of charge in any process.
charge on a body (Q) = n.e
Basic unit of charge qe = qp = 1.6*(10)-19 c
no of electron or proton (n) = 1,2, 3, 4, 5, 6,...........
charge is quantise
A/c to quantization of charge on a body varies in discrete manner.
charge on a body is found to be integral ( not in fraction) of basic unit of charge (e)
Electron is the most fundamental particle of nature which can not be further subdivided into subatomic particle.
charge is Additive
charge is scalar quantity which is added or subtracted according to simple arithmetic rule.
charge is invariate quantity
charge is a invariate quantity i.e independent of velocity or frame of referance.
mass is a variate quantity .
How many types of charges ?
There are mainly two types of charge
1. positive charge 2. negative charge
on electron has negative charge and proton has +ve charge .
Electrostatics force is repulsive and for opposite nature of charge electrostatics force is attractive.
charging due to friction
work function (fi) -: The minimum energy required to remove most loosely bonded electron from metal surface.
It is represented by fi .
The minimum energy required to remove most loosely bonded electrons from isolated gaseous atom is called ionisation energy.
Isolated gaseous atom
when two bodies of different work function rub over each other then due to friction , heat is developed and electron is transferred from lower work function to another body having higher work function . because lower work function body heated firstly .
Body which is -vely charge has gain the electron and body which is +vely charge has loss the electron.
Therefore it is the transferred of electron which is responsible for charging .
Loss of energy occur because electron is bonded by attractive force during loss of electron.
what is coulomb's laws ?
Those laws which tells that when the two charged particle are placed apart then the electrical force acting on them is directly proportional to the product of quantity of charge and inversely proportional to the square of distance between them are called coulomb's laws.
Absolute permittivity of free space is -:
here k is the proportionality constant.
Relative permittivity of medium (Er) = fv/fm
Er>1
The Electric force b/w two point charge decreases in presence of
medium.
The dielectric constant of medium is defined as the factor by which
the electric
force decreases in the presence of medium.
Er>1
The Electric force b/w two point charge decreases in presence of medium.
The dielectric constant of medium is defined as the factor by which the electric
force decreases in the presence of medium.
💥coulomb's law in the vector form-:
The direction of electric force depend on the nature of charge
The electric force is repulsive for same nature of charge
The electric force is directed along the line joining the two point charge.
The electric force is directed radially outward for the same nature of charge and naturally inward for the opposite nature of charge .
The electric force on charge q1 to q2
coulomb's laws obey Newton's third laws of motion . i.e To every action there is equal and opposite reaction.
Electric force on charge q2 due to q1
Electric field
Electric field is the region or surrounding if charge is kept it experience electrostatic force.
only due to presence of charge electric field is produced and due to this electrostatic force is generated.
Electric field Intensity
It is represented by 
To measure the strength of electric field we define a term called electric field intensity .
- Electric force per unit test charge is called electric field intensity.
- we take the direction of electric field in those direction in which force act.
- Electric field intensity at a point p is defined as electric force experience per unit test charge.
Electric field intensity due to a single charge
Electric force on test charge q due to Q
Electric field intensity at point p
r is the distance from charge
Lines of Electric force
Electric field is directed radially outward for single +ve charge.
and radially inward forsingle -ve charge.
Super position principle
A/c to superposition principle To calculate electric field at a point or electric field at a point or electric force on charge due to more than one charge , then electric field or electric force due to each individual charge is calculated and added vectorially , to find net field at point p or net force on charge .
- Electric field or electric force due to each individual charge is independent of presence of other charge .
Net electric field at point p
Electric dipole
Dipole moment for electric dipole is p = q . 2L
Here 2L is the separation b/w two charge .
💥 definition -: Two equal and opposite charge separated by certain distance constitute an electric dipole.
- For electric dipole we can define a term dipole moment which is product of charge and separation b/w two charge .
- dipole moment is vector quantity directed from -ve to +ve charge along dipole axis .
- for ideal dipole separation b/w two charge is very small { 2l tends to 0 }
Electric field due to dipole
case -1 Along dipole axis ( end - on- position )
consider an electric dipole having charge -q and +q separated by 2l , then find the electric field at distance r from centre along dipole axis .
Electric field due to charge +q at point p
Net electric force due to dipole at point p .
case 2 -: Along perpendicular bisector ( broad on position )
consider on electric dipole having charge -q and +q separated by distance 2l . Then find the electric field at distance r on perpendicular bisector.
Electric field due to uniformly charged ring
consider uniformly charged ring of radius a charge 2q then find the electric field at distance r from the centre on the axis of ring.
consider elementary charge (dq) on the ring
Electric field due to elementary charge (dq) at point p .
Great my suman brother
ReplyDeleteVery helpful Notes bro
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