Electrostatic Field Flashcards
What is electrostatic field or electric field? Why is it a vector field ?
The region of space surrounding a charge or a system of charges in which other charged particles experience electrical forces.
It is a vector field because at every point it is defined by a unique vector denoted by Ē
What is a field ? ( physics)
Give e.g for scalar and vector field
In physics the term field generally signifies a quantity that has a unique value at every point in space and may vary from point to point.
Scalar - temperature field pressure field
Vector field - electric and gravitational field
What is electric field strength
Electric field strength or electric intensity or simply electric field at a point in an electric field is defined as the electrostatic force per unit positive charge acting on a unit positive charge placed at that point . Denoted E ->. Has magnitude and direction . SI unit is Newton per coulomb . N/C. Direction is same as force.
What is a test charge?
A test charge is a positive charge of negligibly small magnitude. When placed at a point in an electric field the configuration of charges producing the electric field remains unchanged. The existing electric field in the region does not change significantly due to the placement of test charge.
What is uniform and non uniform electric field?
If the force on a test charge is the same in magnitude and direction at all points in the electric field it is said to be uniform. A uniform field is one in which electric intensity is the same in magnitude and direction at every point in the field
If the force exerted on a test charge varies at different points on the electric field the electric field is said to be non uniform .
How is electric intensity at a point due to a group of charges obtained
The net electric intensity at a point due to a group of charges is the vector sum of the electrical intensities at that point due to each individual charge. That is the principle of superposition holds good for electric fields.
What is a neutral point in an electric field ?
If the resultant electric intensity is zero at any point in an electric field then such a point is called a neutral point .
What is an electric dipole?
A system consisting of two equal and oppositeoinr charges +q and -q separated by a small distance is called an electric dipole.
Define axis of an electric dipole
The straight line joining the negative and positive charge and directed from the negative to the positive charge is called axis of the dipole
Define
Axial line
Equatorial line
A line passing through the positive and negative charges of the electric dipole is called axial line.
A line perpendicular to the axial line and passing through the midpoint of the line joining the positive and negative charges of the electric dipole is called the equatorial line
What is end on position? What is broad side on position?
What is dipole field
A point on the axial line is said to be in end-on position
A point on the equatorial line is said to be in the broad side-on position.
Electric field produced by a dipole is called a dipole field.
How is a uniform electric field represented?
A uniform electric field is represented by a set of equal and equispaced straight lines in the same direction as shown .
What is dipole moment? When is it min and max?
The electric dipole moment is numerically equal to the torque acting on it when it is placed at right angles to a uniform electric field of unit strength . It is measured by the product of magnitude of either of the charges and the sedation between the charges constituting the dipole.
Min - θ = 90°
Max - θ = 0° or 180°
When is a dipole said to be in stable and unstable equilibrium?
What is work done in rotating a dipole from its stable equilibrium position along the field direction through an angle θ ?
When θ = 0° it is stable equilibrium
When θ = 180° it is unstable equilibrium
W = pE (1-cosθ) W = 2pE for θ = 180°
How is avg dipole moment per unit volume of dielectric zero when molecules are polar?
In the absence of external electric field dipole moments of polar molecules orient in random directions
What is induced dipole moment?
In the presence of an external electric field the positive and negative charges of a non polar molecule are pulled apart until the forces acting on them due to external field is balanced by internal forces. Molecule acquires some dipole moment. It is called the induced dipole moment.
What is electric polarisation
The phenomenon of alignment of dipole moments resulting in a layer of positive charge on one side of the dielectric slab and a layer of equal negative charge on the opposite side of the slab . The charges are called induced polarisation charges. Or bound charges since they are bound to their respective molecules.
What does a dielectric do to the external field
Weakens the applied field within the dielectric
What is dielectric breakdown
When a dielectric is placed in a very high electric field the outer electrons get detached from the parent atom and become free electrons . Under this condition dielectric behaves like a conductor and charges are conducted through it. This phenomenon is known as dielectric break down. Dielectric retains its insulating property until it breaks down.
What is dielectric strength? How is it expressed in practice? What is dielectric strength of air?
The maximum value of applied electric field above which dielectric break down occurs is called dielectric strength
Expressed as kilo volt per millimetre kV/mm
Air - 3 kVmm
Define electric lines of force . Who introduced the idea of visualising electric field in terms of lines of force ?
Line of force in an electric field is the imaginary path along which a unit positive charge which is free travels. It may be straight or curved.
What is electric flux ? Scalar or vector ?
The electric flux through a surface is defined as the number of lines if force passing normally through that surface.
It is scalar
What is flux density? What is electric intensity with reference to flux?
Flux per unit area is the flux density.
Electric intensity at a point in an electric field is the number of lines of force passing through a surface of unit area surrounding the point in a direction normal to the surface.
State gauss’s theorem
Gauss’s theorem or Gauss’s law states that the total electric flux through a hypothetical closed surface is always equal to 1/ε0 times the net charge enclosed by the surface.
If electric intensity is the vector description of a field what is the scalar description
Electric potential
Define electric potential. scalar or vector?
Electric potential at a point in an electric field is defined as the amount of work done in moving a unit positive charge from infinity to the point against the electric field.
It is a scalar as its defined in terms of the work done which is scalar
What is the electric potential difference between 2 points in an electric field? scalar or vector?
Potential difference between 2 points in an electric field is defined as the amount of work done in moving a unit positive charge from one point to the other against the electric field.
It is a scalar as its defined in terms of the work done which is scalar
Define 1 volt
The electric potential at a point is said to be 1 volt if one joule of work is done in moving 1 coulomb charge from infinity to the point against the field
Potential difference between 2 points is said to be 1 volt when 1 joule of work is done in moving 1 coulomb charge from one point to the other against the field.
How is electric field a conservative field?
Work done in moving a unit positive charge from one point to another in a electric field is independent of the path taken . It is unique for the 2 given points. Hence electric field is a conservative field.
What is an equipotential surface? What is potential difference between 2 points on an equipotential surface?
If a surface is drawn in an electric field such that the electric potential has the same value at all points on the surface then such a surface is called an equipotential surface. The work done in moving a charge from one point to another in an equipotential surface is zero.
What is equipotential line?
If a line is drawn in an electric field such that the electric potential has the same value at all points on the line then such a line is called equipotential line. Any line drawn on an equipotential surface is an equipotential line.
