Physics (electrostat)

PresentationELECRTOSTATSXII Science.Harsh Kumar

PresentsPhysicsonof

ElectrostaticsThe study of all electrical properties of system having charge, when the charges are in state of rest is known as electrostatics.

ChargeIt is the basic property of a body which explain electrical properties of the body.Charge on a body define by number of free electrons transacted from a body

Unit of charge= C(Coulomb)1C=10C

Q =n e

Types of charge:Positive (+)veNegative (-)veCharge of electron = -1.610CCharge on body = 1CQ = n en=1/1.610 = 6.2510

According to standard module charge consist of Quarks

Charge is Quantized.Charge is associate with mass.Charge is invariant.Charge is conserved.Charge recites on outer surface of a conductor.Charge density is inversely proportional to radius. i.e. Charge recites more at corner then any other place on conductor.For insulator charge recites any where on its surface.Like charges repeal each other and unlike charges attract each other.

Properties of Charge

Properties of charge:Charge can be produced by three ways:Friction.Conduction.Induction.Friction When two charged particles are rubbed each other then one get (+)vely charged and other gets (-)vely charged.E.g.: When we rub glass rod by woolen cloth then glass rod gets (+)vely charged and woolen cloth gets (-)vely charged

Conduction- When two conducting substance attached to each other then charges overlap on one another.

Induction- When a (-)vely charged particle is kept beside (+)vely charged particle then opposite charges are induced on each other.

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Charge are additive in nature.It is a scalar quantity.

SI unit of charge is Coulomb (C).

CGS unit of charge is Stat Coulomb.

1 farad=96500C.

Moving charge with constant velocity produces electric field and magnetic field.

Static charge produces electric field only.

When charge is moving with accelerated motion then it produces electric field, magnetic field and radiates electro magnetic wave.

Coulombs lawThe force of attraction between two point charges is directly proportional to magnitude of product of both charges and inversely proportional to square of distance between them.F q q F 1/r

From &

where K is proportionality constant F=K q q/r

K = 1 (in CGS unit)K = 1/4 (in SI unit)K = 910(in air)Where is absolute permittivity in free space and is relative permittivity of medium.For air = 1For water = 81Coulombs law is also called inverse square law.The force of attraction is a central force, it is added by vector law of addition.

Charge DensityIt is a scalar quantity, there are three types of charge density.Linear charge density:- Charge per unit length is called linear charge density. It is denoted by .=Q/lSurface charge density:- Charge per unit surface area is called surface charge density. It is denoted by .=Q/A

Volume charge density:- charge per unit volume is called volume charge density. It is denoted by .=Q/V

Electric fieldElectric field is the field where a force acts on any charged particle.Electric field intensity:- Electric field intensity at a point is the force experienced by unit (+)ve charge at that point. It is denoted by E.It is a vector quantity.Its unit is N/C.It is added by vector law of addition.

E=F/q

Electric field lines or Electric lines of force:-

Electric lines of force is a curved imaginary lines which denotes electric field.

Properties of electric field lines:-Electric lines of force never interact each other.It emerges normally to a conductor.Number of lines of force per unit area gives strength of electric field.

Tangent on lines of force gives direction of electric field.

Electric lines of force emerges normally from (+)ve charge and terminates to (-)ve charge.

EE

E > E

E

Electric lines of force never made a close loop.Electric lines of force per unit surface area is called electric flux.

Electric field intensity due to unit (+)ve charge in an electric fieldLet us conceder a point P at distance r from a test charge q.A unit (+)ve charge q is kept at P, we have to found the electric field intensity due to unit (+)ve charge.

(q) (q)A r PF = (q.q/4 r)We know that =1 for airE=F/q E = (q.q/q 4 r)

E=(q/4 r)

Electric fluxLines of force in a unit surface area is called electric flux.It is dot product of electric field intensity and surface area. It is denoted by .

=E.ds =E ds cos

Case 1-if =0=E dsCase 2-if =90=0

Small area is a vector quantity, where as large area is a scalar quantity.The total flux emerges from a close surface is equal to 1/ times of charge=q/Flux comes out from a closed cube is q/Where q is charge enclosed.

DipoleA system of two same but opposite charges placed at some distance is known as Dipole.It is a combination of two charges of same magnitude but opposite nature kept at some distance apart.

-q+q2LLLPDipole Moment:- It is the product of 1 charge and distance between two charges.It is a vector quantity.It is denoted by P .Its direction is from (-)ve to (+)ve charge.

Torque acting on a electric dipole in an electric field

BEE+q-q2LAEOCLet us consider a dipole of dipole moment P in an electric field E due to opposite nature of charge on dipole it experiences electric force in opposite direction which is converted into Torque and dipole starts rotating

=Force distance

= F (BC)= q E 2L sinsin=BC/AB BC=2L sin

=P E sin

=P E

Work done by electric dipole in an electric field

BEE+q-q2LAEOCWork done of electric dipole can be given as :dw = dPutting value of from eq .dw = P E sin dIntegrating both side with taking proper limit. dw = P E sin d

w = P E [-cos]

w= P E [-cos - (-cos)]

w = P E [cos - cos]0w

If = 0 ; = w = P E [1-cos]

Gausss lawFlux linked with closed surface is 1/ times of a charge kept in that close surface.i.e. = q/

Proof:

drrdsE q

d = E . dsConsider a charge q enclosed in a Gaussian sphere of radius r. Let an small area ds at any point on sphere; whose direction is along the direction of electric field intensity.

Then Flux linked with this small area :

d = E . dsd = E ds cosd = E ds cos0 [ =0]d = E dsd = (q/4 r ) dsIntegrating along closed surface d = ds = (q/4 r) (4r - 0) = q/

drrdsE q

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XII Science.Harsh KumarPresented byof08RollNo.