Important Questions of Electrostatics
In this post, some of the important questions of electrostatics are given. It includes definition of static electricity, meaning of molecules and atoms, positive ions and negative ions, glass rubbed with silk, importance of permittivity, absolute permittivity of air, relative permittivity, coulomb first law, coulomb second law, definition of electric field, definition of lines of force, current does not flow in dielectric material, definition of electric field, electric intensity, dielectric strength, potential and factor of safety.
Explain the term: Static – electricity
Static
electricity
When two charges bodies are separated by insulating
medium, the charges remain stationary on the body. This is called static
electricity.
The branch of engineering which deals with the study
of static – electricity is called electro statics.
What do you mean by the molecule and atoms?
Molecule
The smallest part of the substance is called molecule.
Atoms
A molecule consists of one or more substance is called
as atoms.
When atom becomes positive ion and negative ion?
Positive
ion and Negative ion
If an atom loses an electron, it becomes positive
charged. This atom is known as positive ion. Similarly, when atom gain an
electron, it becomes negative charged.
Describe the main reason for production of electro static charge when glass is rubbed with silk.
Electro – static charges
When glass is rubbed with silk, glass loses electrons
to silk and therefore it becomes positive charged. Similarly, when ebonite is
rubbed with fur, ebonite gains electrons from fur and becomes negative charged.
Describe the importance of permittivity.
Importance
of permittivity
The permittivity affects the magnitude of the force
between two-point charges. Higher the value of permittivity placed between two-point
charges lesser the force between them and vice versa.
State the value of the absolute permittivity for air.
Absolute Permittivity
The absolute permittivity of the air ( ε0 )
or vaccum is minimum and its value is limited to 8.854 × 10-12 farad
/ meter. The value of absolute permittivity of other material is more than ε0.
Define: relative permittivity
Relative
permittivity ( εr )
The ratio of the absolute permittivity of some
material to the absolute permittivity of the air is called as relative
permittivity. Therefore
εr
= ε / ε0
Where
εr =
Relative permittivity of the material
ε = Absolute
permittivity of the material
ε0 =
Absolute permittivity of the air ( Farad / Meter )
State the coulomb’s first and second law.
Coulomb first law
The first law explains the nature of the force between
two charged bodies. It states that’ like charges of electricity repel each
other whereas unlike charges attract each other’.
Coulomb second
law
The second law explains the magnitude of the force
between two charges. It states that ‘The force between two charges is directly
proportional to the magnitude of the charges and inversely proportional to the
square of the distance between two charges.’ Therefore
F α ( Q1 × Q2 ) / d2
F =
k ( Q1 × Q2 / d2 )
Q1 = Magnitude of the
charge 1
Q2 = Magnitude of the
charge 2
d2 = Distance between two charges
k = Constant
= 1 / 4πε0εr
Define: Electric field
Electric
field
The limited space region around charged body in which
an electric charge experiences a force of attraction or repulsion is called an
electric field.
Define: Electric lines of force or flux
Flux
(Electric line of force)
The electric imaginary field lines around charged body
is called as electric lines of flux.
Why electric lines of force do not intersect?
Electric Lines of Force
The direction of the electric lines of force is from
positive charged body to the negative charged body. The electric lines of force
do not intersect because at the point of the intersection there are two
directions of the field and it is not possible.
Why current does not flow in the dielectric material?
Dielectric Material
When the potential difference is applied across an insulating
material, current does not flow because valance electrons are tightly bound to
its nucleus and no free electrons are available for conduction of current.
Define: Electric flux, Electric flux intensity and Electric Potential
Electric flux
The electric field is represented by electric flux
lines. The numbers of lines of force eliminating from positive charged particle
(or body) is called as electric flux. Its unit is coulomb.
Electric flux intensity
It is defined as electric flux passing through unit
area at the right angle to the direction of the field. Its unit is
coulomb/meter2
OR
It is defined as force experienced by a unit positive
charge placed at that point.
Electric potential
The electrical potential at any point is equal to the
work done required to bring a unit positive charge from infinity to that point
against the electric field.
Its unit is joule / coulomb.
Define: Electric potential gradient, Electric field intensity and Dielectric Strength
Electric potential gradient
It is defined as the rate of change of potential with
distance. Its unit is volt / meter.
Electric field intensity
It is defined as force experienced by the unit
positive charge placed at that point.
Its unit is Newton / coulomb.
Dielectric strength
It is ability of the dielectric material to withstand
against breakdown.
The dielectric strength is defined as the maximum
potential difference which can withstand by the dielectric material without
breakdown of it.
It is expressed in kV / mm.
Explain the term: Induction
Induction
It is phenomenon in which
the uncharged body gets charged by proximity charged body.
State the potential of the earth.
The potential of the earth
is zero.
Define: Potential
Potential
It is defined as the work
done per unit charge.
Define: Factor of safety for dielectric
Factor of safety
It is defined as the ratio
of dielectric strength of insulator to the electric field strength in the
dielectric.
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