Electrostatics
ALLEN°
ELECTROSTATICS
THEORY
INTRODUCTION
"Electrostatics" pertains to elcctric charges at rest or to fields or phenomena produced by stationary
charge(s).
ELECTRIC CHARGE
produces
Charge of a material body or particle is the property (acquired or natural) due to which it
andexperiences electricaland magnetic effects. Some of naturally occurring charged particles are
electrons, protons, a-particles etc.
we use
Charge is a derived physical quantity & SIunit of charge is coulomb. In practice
mC(10C), uC (10C), nC(10-°C) etc.
C.G.S. unit of charge = electrostatic unit = esu.
lcoulomb =3x 10 esu of charge
Dimensional formula of charge = [M°L'T'I]
1.1 PROPERTIES OF CHARGE
or deficiency of electrons.
Charge isa scalar quantity :It adds algebraically and represents excess
charge Charging a body implies
A Charge is of two types: (i) Positive charge and (ii) Negative
Positively charged body means loss of
transfer of charge (electrons) from one body to another.
means excess of electrons.Charges
electrons i.e. deficiency of electrons. Negatively charged body
charges with opposite electrical sign attract
with the same electrical sign repel each other, and
each other.
charge (sum of positive and negative)remains
Chargeis conserved: In an isolated system, total
Constant.
always exists in integral multiples of a fundamental
A Charge is quantized : Charge on any body
magnitude of charge on clectron (le = l.6x 10-19
unit of electriccharge. This unit is cqual to the
coulomb). So charge on anybody is Q = tne,
where n is an integer and e is the charge of the
quantizationof charge or atomicityof charge
electron. Millikan's oildrop experiment proved the
Comparison of charge and mass : Weare familiar
with role of mass in gravitation, and we have
compare the twO as shown below
just studied some features of electric charge. We can
1
, JEE-Physics ALLEN
Table - Chargevls Mass
Mass
Charge Mass of a body is a positive quantity.
Electiccharge canbe positive,
(1)
(
negative or zcr0. Mass ofa body increases with jits velocity:
(2)
|(2) Charge carried by a body docs
m,
m =
VI-v'/c'
where cis velocity of lightin
not dependupon velocity of the
vacuum, mis the mass of the body moving wth
velocity vand m, is rest mass of
the body
be establich
(3) The quantization of mass is yet to
(3) Charge is quantized. be changed int
(4) Mass is not conserved as it can
(4) Electric charge is always conserved. energy and vice-versa.
(5) The gravitational force between two masses i
(S) Force between charges can be
always attractive.
attractive or repulsive, accordingly
as charges are unlike or like charges.
charge cannot exist without mass though mass
can exit
Charge is always associated with mass, i.e.,
neutrino which have no (rest) mass can never have
without charge. The particle such as photon or
acharge. independent of frame of refererç:
Charge is relativistically invariant: This means that charge is
property is worth mentioning s
i.e., chargeon a body does notchange whatever be its speed. This
with increase inspeed
in contrast to charge, the mass of a body depends on its speed and increases
uniform motion produss
Acharge at rest produces only electric field around itself, a charge having
motion emit
electric as well as magnetic field around itself while a charge having accelerated
electromagnetic radiations.
1.2 CHARGING OF A BODY
Abodycan be charged by means of (a) friction, (b) conduction, (c) induction
1.2.1 CHARGING BY FRICTION: When a neutral body is rubbed against other neutral body
some electrons are transferred from one body to other. The body which can hold electrons tgn
draws some electrons and the body which can not hold electrons tightly, loses some electrons.
body which draws electrons becomes negatively charged and the body which loses electrons bect
positively charged.
A B
After rubtbing
TTI
A
Neutral
2
ALLEN°
ELECTROSTATICS
THEORY
INTRODUCTION
"Electrostatics" pertains to elcctric charges at rest or to fields or phenomena produced by stationary
charge(s).
ELECTRIC CHARGE
produces
Charge of a material body or particle is the property (acquired or natural) due to which it
andexperiences electricaland magnetic effects. Some of naturally occurring charged particles are
electrons, protons, a-particles etc.
we use
Charge is a derived physical quantity & SIunit of charge is coulomb. In practice
mC(10C), uC (10C), nC(10-°C) etc.
C.G.S. unit of charge = electrostatic unit = esu.
lcoulomb =3x 10 esu of charge
Dimensional formula of charge = [M°L'T'I]
1.1 PROPERTIES OF CHARGE
or deficiency of electrons.
Charge isa scalar quantity :It adds algebraically and represents excess
charge Charging a body implies
A Charge is of two types: (i) Positive charge and (ii) Negative
Positively charged body means loss of
transfer of charge (electrons) from one body to another.
means excess of electrons.Charges
electrons i.e. deficiency of electrons. Negatively charged body
charges with opposite electrical sign attract
with the same electrical sign repel each other, and
each other.
charge (sum of positive and negative)remains
Chargeis conserved: In an isolated system, total
Constant.
always exists in integral multiples of a fundamental
A Charge is quantized : Charge on any body
magnitude of charge on clectron (le = l.6x 10-19
unit of electriccharge. This unit is cqual to the
coulomb). So charge on anybody is Q = tne,
where n is an integer and e is the charge of the
quantizationof charge or atomicityof charge
electron. Millikan's oildrop experiment proved the
Comparison of charge and mass : Weare familiar
with role of mass in gravitation, and we have
compare the twO as shown below
just studied some features of electric charge. We can
1
, JEE-Physics ALLEN
Table - Chargevls Mass
Mass
Charge Mass of a body is a positive quantity.
Electiccharge canbe positive,
(1)
(
negative or zcr0. Mass ofa body increases with jits velocity:
(2)
|(2) Charge carried by a body docs
m,
m =
VI-v'/c'
where cis velocity of lightin
not dependupon velocity of the
vacuum, mis the mass of the body moving wth
velocity vand m, is rest mass of
the body
be establich
(3) The quantization of mass is yet to
(3) Charge is quantized. be changed int
(4) Mass is not conserved as it can
(4) Electric charge is always conserved. energy and vice-versa.
(5) The gravitational force between two masses i
(S) Force between charges can be
always attractive.
attractive or repulsive, accordingly
as charges are unlike or like charges.
charge cannot exist without mass though mass
can exit
Charge is always associated with mass, i.e.,
neutrino which have no (rest) mass can never have
without charge. The particle such as photon or
acharge. independent of frame of refererç:
Charge is relativistically invariant: This means that charge is
property is worth mentioning s
i.e., chargeon a body does notchange whatever be its speed. This
with increase inspeed
in contrast to charge, the mass of a body depends on its speed and increases
uniform motion produss
Acharge at rest produces only electric field around itself, a charge having
motion emit
electric as well as magnetic field around itself while a charge having accelerated
electromagnetic radiations.
1.2 CHARGING OF A BODY
Abodycan be charged by means of (a) friction, (b) conduction, (c) induction
1.2.1 CHARGING BY FRICTION: When a neutral body is rubbed against other neutral body
some electrons are transferred from one body to other. The body which can hold electrons tgn
draws some electrons and the body which can not hold electrons tightly, loses some electrons.
body which draws electrons becomes negatively charged and the body which loses electrons bect
positively charged.
A B
After rubtbing
TTI
A
Neutral
2
