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Electrostatic field

The space around a point charge in which the force of interaction can be experienced by placing another

charge.

The electric field line due to a positive charge is always outward

The lecetric field line due to negative charge is always inward.

Electric field Intensity

E = F(r) /q0

If q0 = 1 then E(r) = F(r)

The electric field intensity at a point in the field is defined as the force experience by a unit test charge

at that point. It is vector quantity

Unit of E = Nc-1

Dimension = MLT-2

/AT = [MLT-3

A-1

]

Numerical: calculate force on an electron in electric field of 5 x 104N/c due north?

Solution. Given E = 5 x 104N/c

F =?

We know that E= F/q0, f = q0 x E

= -1.6 x 10-19 x 5 x 104

= - 8.0 x 10-15

N (towards south)

Electric field intensity due to a point charge:

Let us consider a point charge q is at 0. Suppose p is the point in the field where we want to calculate

the E. now a q0is at P such that OP = r

According to coulombs law:

F =

By definition of field intensity

E = F/q0

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So divide eq I on both side by q0

F/q0 =

E =

= r

Q1. What is nature of symmetry due to a single point charge?

The electric field due to single point charge is spherical symmetry or radial field.

Electric field intensity due to a number of charges

Let us consider a system of charge q1, q2, q3.qn. suppose a unit positive test charge is at o.

Such that r1, r2, r3. Rn the respective position of each charge

F1 =

F2 =

Fn =

Therefore E1 = F1/q0 , E2= F2/q0 En= Fn/ q0

Physical significance of electric field line:

The physical significance of electric field line at a point is help to calculate the magnitude and direction

of force experience by test charge q0 at that point.

Electric line of forces/electric field line (Faraday)

The Electric line of forces are defined as the straight or curved path such that tangent to it at any point

gives the direction of Electric field intensity at that point.

Properties:

1. Electric field line are discontinuous curves b/c they start from a positive charge and end atnegative charge and does not form a loop (o)

2.

The tangent to it at any point gives the direction of Electric field intensity at that point.3. No two electric line of forces can intersect each other. Because when two field line intersect

each other at a point they gives two direction for a single point which is impossible

4. The electric field of line are always normal to the surface of a conductor.5. Electric line of forces are contract longitudinally. It can be help in case of unlike charges.6. They exert lateral pressure.

It can held only in case of like charges.

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Electric dipole:

An electric dipole consist a pair of equal and opposite point charges are separated by a small

distance of 2a. the total charge on an electric dipole is always = 0

Dipole moment:

The dipole moment of any electric dipole is defined as the product of either of charges and

distance between them.

It is a vector quantity because its direction is from negative charge to positive charge.

Unit of P = cm

Ideal dipole : an electric dipole is said to be an ideal dipole when the charge is large and distance

is much smaller. The ideal dipole does not have size.

Dipole field: the space around an electric dipole in which electric effect of dipole can be

experienced.

Electric field intensity due to an electric dipole:

An electric dipole consist a pair of equal and opposite point charges are separated by a small

distance of 2a.

There are two cases arise:

1. To find the electric field intensity at axial line of dipole.2. To find the lectric field intensity at Equitorial line of dipole.

To find the electric field intensity at axial line:

Let us consider an electric dipole having chargeq at A and +q at B where AB = 2a & o be the centre of

dipole suppose P is the pont on its axial line where we want to calculate the net field intensity. Such that

OP = r. suppose E1 is the field intensity at P due toq at A and E is the field intensity at P due to +q at B.

there fore

Derivation

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E an Equatorial line of electric Dipole

Let us consider an electric dipole having chargeq at A and + q at B such that AB = 2a where o is the

center. Suppose E1 is the field at P due toq at A and E is the field at P due to +q at B. suppose P is the

point where we want to calculate the net field intensity on the equal line. Such that OP =r

derivation