1.Electric charges and Fields Xplore Learning Centre
Electrostatics deals with the study of forces, fields and potentials arising from static
charges. OR The branch deals with study of charges at rest.
ELECTRICITY: The flow of charges is called as electricity. The name electricity is coined
from the Greek word "electron " meaning amber.
ELECTRIC CHARGE: An basic entity (particle) of each matter which experience force of
attraction or repulsion is called the electric charge. Hence there were only two kinds of
charges were named as positive and negative by the American scientist Benjamin
Franklin.
If an object possesses an electric charge, it is said to be electrified or charged. When
it has no charge it is said to be neutral. Hence process of making objects charged is called as
electrification or charging.
GOLD-LEAF ELECTROSCOPE
A simple apparatus to detect charge on a body is the "gold-leaf electroscope."
Construction and working: It consists of a vertical metal rod housed in a box, with
two thin gold leaves attached to its bottom end. When a charged object touches the metal
knob at the top of the rod, charge flows on to the leaves and they diverge. The degree of
divergence is an measures the amount of charge.
To electrify a neutral body, we need to add or remove one kind of charge. When we say
that a body is charged, we always refer to this excess charge or deficit of charge. In solids,
some of the electrons, being less tightly bound in the atom, are the charges which are
transferred from one body to the other.
A body can thus be charged positively by losing some of its electrons. Similarly, a
body can be charged negatively by gaining electrons.
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, 1.Electric charges and Fields Xplore Learning Centre
CONDUCTORS AND INSULATORS
The substances which allow electricity to pass through them easily are called
Conductors. They have electric charges (electrons) that are comparatively free to move
inside the material.
Example- Metals, human and animal bodies and earth etc.
The substances which do not allow electricity to pass through them easily are called
Insulators. There are no free electric charges inside material.
Examples- Glass, porcelain, plastic, nylon, wood etc.
CHARGING METHODS
The object can be acquired a charge by following three process.
1)Charging by friction: When we rub a glass rod with silk, some of the electrons from the
rod are transferred to the silk cloth. Thus the rod gets positively charged and the silk gets
negatively charged. Here both bodies get oppositely charged.
2)Charging by contact: When a charged body brought in contact with uncharged body
then both the bodies acquire the same charge.
3)Charging by induction: When charging a conductor by induction, a charged object is
brought close to but does not touch the neutral conductor. In the end the conductor acquire
charge of opposite sign as the charge on the object.
NOTE: The process of sharing the charges with the earth is called grounding or
earthing. Earthing provides a safety measure for electrical circuits and appliances.
How to make two bodies charged oppositely by method of induction?
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, 1.Electric charges and Fields Xplore Learning Centre
BASIC PROPERTIES OF ELECTRIC CHARGE
1. Additivity of charges: The total charge of the system is the algebraically sum of all
the charges within the system. If a system contains 'n' charges q1, q2, q3, ..., qn, then
the total charge of the system is q1 + q2 + q3 + ... + qn .
2. Charge is conserved: Charges are neither created nor destroyed but only transfer
from one body to another such that total charge of the isolated system is always
conserved (constant).
3. Quantisation of charge: The charges are integral multiples of a basic unit of charge
denoted by e. Thus charge Q on a body is always given by
Q = ±ne
where n is any integer, positive or negative & e =1.602×10-19C
Note: The quantisation of charge was first experimentally demonstrated by Millikan
in 1912.
>SI Unit of charge is called a 'Coulomb' and is denoted by the symbol C.
>One coulomb: Charge flowing through a wire in 1 s if the current is 1 A.
“Thus, there are about 6 × 1018 electrons in a charge of –1C”.
COULOMB’S LAW OF ELECTROSTATIC
"Coulomb measured the force between two point charges and found that it varied
inversely as the square of the distance between the charges and was directly proportional
to the product of the magnitude of the two charges and acted along the line joining the two
charges.”
If two point charges 𝑞 , 𝑞 are separated by a distance 'r' in vacuum, then
magnitude of the force (F) between them is given by
𝟏 𝒒𝟏 𝒒𝟐 r
F= 𝑞 𝑞
𝟒𝝅𝜺𝟎 𝒓𝟐
Where 𝑘 = = 9 × 109 Nm2C-2
And 𝜀 =permittivity of free space = 8.854×10-12 C2N-1m-2
When 𝑞 = 𝑞 = 1𝐶 and r = 1m then F = 9 × 109N
Define One coulomb:
1C is the charge that when placed at a distance of 1 m from another charge of the same
magnitude in vacuum experiences an electrical force of repulsion of magnitude 9 × 10 9 N.
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Electrostatics deals with the study of forces, fields and potentials arising from static
charges. OR The branch deals with study of charges at rest.
ELECTRICITY: The flow of charges is called as electricity. The name electricity is coined
from the Greek word "electron " meaning amber.
ELECTRIC CHARGE: An basic entity (particle) of each matter which experience force of
attraction or repulsion is called the electric charge. Hence there were only two kinds of
charges were named as positive and negative by the American scientist Benjamin
Franklin.
If an object possesses an electric charge, it is said to be electrified or charged. When
it has no charge it is said to be neutral. Hence process of making objects charged is called as
electrification or charging.
GOLD-LEAF ELECTROSCOPE
A simple apparatus to detect charge on a body is the "gold-leaf electroscope."
Construction and working: It consists of a vertical metal rod housed in a box, with
two thin gold leaves attached to its bottom end. When a charged object touches the metal
knob at the top of the rod, charge flows on to the leaves and they diverge. The degree of
divergence is an measures the amount of charge.
To electrify a neutral body, we need to add or remove one kind of charge. When we say
that a body is charged, we always refer to this excess charge or deficit of charge. In solids,
some of the electrons, being less tightly bound in the atom, are the charges which are
transferred from one body to the other.
A body can thus be charged positively by losing some of its electrons. Similarly, a
body can be charged negatively by gaining electrons.
Coaching for 8 -10th, PU I & II (Sci. & Commerce), NTSE, Olympiad, KVPY, NDA, CET, NEET, JEE. Call: 9663320948 Page 1
, 1.Electric charges and Fields Xplore Learning Centre
CONDUCTORS AND INSULATORS
The substances which allow electricity to pass through them easily are called
Conductors. They have electric charges (electrons) that are comparatively free to move
inside the material.
Example- Metals, human and animal bodies and earth etc.
The substances which do not allow electricity to pass through them easily are called
Insulators. There are no free electric charges inside material.
Examples- Glass, porcelain, plastic, nylon, wood etc.
CHARGING METHODS
The object can be acquired a charge by following three process.
1)Charging by friction: When we rub a glass rod with silk, some of the electrons from the
rod are transferred to the silk cloth. Thus the rod gets positively charged and the silk gets
negatively charged. Here both bodies get oppositely charged.
2)Charging by contact: When a charged body brought in contact with uncharged body
then both the bodies acquire the same charge.
3)Charging by induction: When charging a conductor by induction, a charged object is
brought close to but does not touch the neutral conductor. In the end the conductor acquire
charge of opposite sign as the charge on the object.
NOTE: The process of sharing the charges with the earth is called grounding or
earthing. Earthing provides a safety measure for electrical circuits and appliances.
How to make two bodies charged oppositely by method of induction?
Coaching for 8 -10th, PU I & II (Sci. & Commerce), NTSE, Olympiad, KVPY, NDA, CET, NEET, JEE. Call: 9663320948 Page 2
, 1.Electric charges and Fields Xplore Learning Centre
BASIC PROPERTIES OF ELECTRIC CHARGE
1. Additivity of charges: The total charge of the system is the algebraically sum of all
the charges within the system. If a system contains 'n' charges q1, q2, q3, ..., qn, then
the total charge of the system is q1 + q2 + q3 + ... + qn .
2. Charge is conserved: Charges are neither created nor destroyed but only transfer
from one body to another such that total charge of the isolated system is always
conserved (constant).
3. Quantisation of charge: The charges are integral multiples of a basic unit of charge
denoted by e. Thus charge Q on a body is always given by
Q = ±ne
where n is any integer, positive or negative & e =1.602×10-19C
Note: The quantisation of charge was first experimentally demonstrated by Millikan
in 1912.
>SI Unit of charge is called a 'Coulomb' and is denoted by the symbol C.
>One coulomb: Charge flowing through a wire in 1 s if the current is 1 A.
“Thus, there are about 6 × 1018 electrons in a charge of –1C”.
COULOMB’S LAW OF ELECTROSTATIC
"Coulomb measured the force between two point charges and found that it varied
inversely as the square of the distance between the charges and was directly proportional
to the product of the magnitude of the two charges and acted along the line joining the two
charges.”
If two point charges 𝑞 , 𝑞 are separated by a distance 'r' in vacuum, then
magnitude of the force (F) between them is given by
𝟏 𝒒𝟏 𝒒𝟐 r
F= 𝑞 𝑞
𝟒𝝅𝜺𝟎 𝒓𝟐
Where 𝑘 = = 9 × 109 Nm2C-2
And 𝜀 =permittivity of free space = 8.854×10-12 C2N-1m-2
When 𝑞 = 𝑞 = 1𝐶 and r = 1m then F = 9 × 109N
Define One coulomb:
1C is the charge that when placed at a distance of 1 m from another charge of the same
magnitude in vacuum experiences an electrical force of repulsion of magnitude 9 × 10 9 N.
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