Electrostatics and Electric Field
Electric charges and fields
Electric charges is of two types positive and negative loss of electrons gives positive charge and gain of electrons gives negative charge to a body
SI unit of charge is Coulomb
Dimensional formula is [AT]
Quantization of charge
The charge on a body is integral
multiple of e
Q=ne
Charge distribution
Charges distributed along the line but is called linear charge density that is charge per unit length is called linear charge density
= ∆q/∆l
Charges distributed over a surface area then it is called surface charge density
=∆q/∆S
Main charge is distributed over entire volume of a body that is call volume charge density
=∆q/∆V
Coulomb's Law
If q1 and q2 be the two stationary point charges in free space separated by a distance r then force of attraction or repulsion between them is
F=k( q1 q2 )/r^2
Where k =9×10^9=1/4πEo
Eo -- electric permittivity of free space
Value is equal to 8.85×10^-12
If some dielectric medium (K) is field between the charges then coulomb force become
F'=F/K
What is electric Dipole
Dipole consists of two equal and opposite charges separated by a small distance
Dipole moment of a dipole is defined as the product of magnitude of either charges and the distance between them
(+q)---------------------------------(-q)
2a
Dipole moment (p) = distance ×charge
= 2aq
Dipole moment is a vector quantity its direction is from negative to positive charge SI unit is coulomb metre
Dimensional formula is [LTA]
Dipole moment is a vector quantity its direction is from negative to positive charge SI unit is coulomb metre
Dimensional formula is [LTA]
Electric field intensity at any point on axis of dipoleAuto point restaurant r from the centre of a reliable along its axial line electric field due to a dipole is equal toE= k 2pr/(r^2-a^2)^2K = 9×10 ^9If r>>aThenE= k 2p/r^3
When a dipole is placed in an external electric field making an angle with the direction of the uniform electric field
It experiences a torque = pE sin¢
Work done
An electric dipole initially kept in an uniform electric field making an angle and rotated so as to finally substance and another angle then the work done for rotating the dipole is
W= pE (cos¢2. - cos ¢1)
Potential energy of a dipole
The amount of work done in rotating an electric dipole from a direction perpendicular to electric field to a particular direction
U = -pE cos ¢
potential energy of an electric dipole is a scalar quantity that is measured in joule
Sun Dec 25, 2022
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