CHAPTER-1
ELECTRIC CHARGES AND FIELDS
INTRODUCTION:
Electromagnetism is a science of combination of electrical and magnetic phenomenon.
Electromagnetism can be divided into two parts.
1. Electrostatics: It deals with the study of charges at rest.
2. Electrody namies: 1t deals with the study of charges in motion.
Electromagnetic interactions involve particles that have a property called electric
charge, an attribute that is as fundamental as mass. Just as objects with mass are accelerated
by gravitational forces, so electrically charged particles are accelerated by electric forces.
Ancient Greeks discovered that after they rubbed amber with wool, the amber could
attract other objects. Today we say that the amber has acquired a net "electric charge". The
word electric' is derived from Greek word 'elektron' meaning amber. Plastic rods and fur
are particularly good for demonstrating electrostatics. When we rub plasticrods with fur. the
plastic rods become charged and repel cach other. Similarly glass rods rubbed with silk
repel each other. But acharged rubber rod attracts a charged glass rod. These experiments
suggested that there are exactly two kinds of electric charges. Benjamin Franklin suggested
calling these two kinds of charges as negative and positive. The kind of charge acquired
by rubber and silk is negative and the kind of charge acquired by fur and glass rod is
positive,
TWOTYPES OF CHARGES
There are two types of electric charges in Nature. When two glass rods rubbed
against silk are brought close to each other they repel cach other. Similarly two plastic rods
rubbed with fur or cat skin repel cach other. On the other hand, a rubbed glass rod and a
rubbed plastic rod attract each other.
These observations show that the charges on the glass TOds are different in nature from
those on the plastic rods. That is, there are two types of charges in Nature. Also similar
charges on glass rods repel each other and similar charges on plastic rods also repel each
other. But different types of charges on a glass rod and a plastic rod attract each other. By
, FLECTRICCHARGESANDFIELDS
convention, the charges that appear on glass rods rubbed with silk were called positive
charges and the charges found on plastic rods rubbed with fur were called negative charoee
Therefore when aglass rod is rubbed with silk cloth. glass rod acquires positive
charge and silk acquires negative charge Similarly when a plastic or rubber rod i
rubbed with fur or cat skin, a plastic or rubbed rod acquires negative charge and fur
or catskin acquires positive charge
ELECTRIC CHARGE AND STRUCTURE OF MATTER:
"Electric charge is an intrinsic property of the elementary particles of matter
which gives rise to electric force benveen various objects") From the study of atomic
structure, we know that an atom consists of a central part called nucleus arnd around the
nucleus there are a number of electrons revolving in different paths or orbits. The nucleus
contains protons and neutrons. A proton is apositively charged particle while a neutron has
no charge. Therefore, the nucleus of an atom bears a positive charge. An electron is a
negatively charged particle having negative charge equal to the positive charge on a proton.
Nomally, the number of electrons is equal to the number of protons in an atom. Therefore,
an atom is neutral as a whole; the negative charge on electrons cancelling the positive charge
on protons. This leads to the conclusion that under ordinary conditions, a body is neutral,
i.e. it exhibits no charge.
The above simplified picture of atomic structure shows that matter is electrical in
nature ie. matter contains particles of electricity namiëly, protons and electrons. If the
number of protons is equal to the number of electrons in a body, the resultant charge is zero
and the body willbe electrically neutral. For example, the paper of this bok is electrically
neutral because it has the same number of protons and electrons.
If from a neutral body, some electrons are removed, the protons outnumber the
electrons. Consequently, the body atains a positive charge. Hence, a positively charged
body has deficit of electrons from the normal due share.
If aneutral body is supplied with electrons, then electrons outnumber the protons. As
a result, the body acquires a negative charge. Hence, a negatively charged body has an
excess of electronsfrom the normal due share So, when a body has deficiency or
excess of electrons from normal due share, it is said to be charged or electrified.
How does a glass rod rubbed with silk acquire a positive charge can be explained on
the basis of atomic structure of materials? Electrons farther away from the nucleus are loosely
bound within the atonms. Some of these electrons may be relatively easily removed by
ELECTRIC CHARGES AND FIELDS
INTRODUCTION:
Electromagnetism is a science of combination of electrical and magnetic phenomenon.
Electromagnetism can be divided into two parts.
1. Electrostatics: It deals with the study of charges at rest.
2. Electrody namies: 1t deals with the study of charges in motion.
Electromagnetic interactions involve particles that have a property called electric
charge, an attribute that is as fundamental as mass. Just as objects with mass are accelerated
by gravitational forces, so electrically charged particles are accelerated by electric forces.
Ancient Greeks discovered that after they rubbed amber with wool, the amber could
attract other objects. Today we say that the amber has acquired a net "electric charge". The
word electric' is derived from Greek word 'elektron' meaning amber. Plastic rods and fur
are particularly good for demonstrating electrostatics. When we rub plasticrods with fur. the
plastic rods become charged and repel cach other. Similarly glass rods rubbed with silk
repel each other. But acharged rubber rod attracts a charged glass rod. These experiments
suggested that there are exactly two kinds of electric charges. Benjamin Franklin suggested
calling these two kinds of charges as negative and positive. The kind of charge acquired
by rubber and silk is negative and the kind of charge acquired by fur and glass rod is
positive,
TWOTYPES OF CHARGES
There are two types of electric charges in Nature. When two glass rods rubbed
against silk are brought close to each other they repel cach other. Similarly two plastic rods
rubbed with fur or cat skin repel cach other. On the other hand, a rubbed glass rod and a
rubbed plastic rod attract each other.
These observations show that the charges on the glass TOds are different in nature from
those on the plastic rods. That is, there are two types of charges in Nature. Also similar
charges on glass rods repel each other and similar charges on plastic rods also repel each
other. But different types of charges on a glass rod and a plastic rod attract each other. By
, FLECTRICCHARGESANDFIELDS
convention, the charges that appear on glass rods rubbed with silk were called positive
charges and the charges found on plastic rods rubbed with fur were called negative charoee
Therefore when aglass rod is rubbed with silk cloth. glass rod acquires positive
charge and silk acquires negative charge Similarly when a plastic or rubber rod i
rubbed with fur or cat skin, a plastic or rubbed rod acquires negative charge and fur
or catskin acquires positive charge
ELECTRIC CHARGE AND STRUCTURE OF MATTER:
"Electric charge is an intrinsic property of the elementary particles of matter
which gives rise to electric force benveen various objects") From the study of atomic
structure, we know that an atom consists of a central part called nucleus arnd around the
nucleus there are a number of electrons revolving in different paths or orbits. The nucleus
contains protons and neutrons. A proton is apositively charged particle while a neutron has
no charge. Therefore, the nucleus of an atom bears a positive charge. An electron is a
negatively charged particle having negative charge equal to the positive charge on a proton.
Nomally, the number of electrons is equal to the number of protons in an atom. Therefore,
an atom is neutral as a whole; the negative charge on electrons cancelling the positive charge
on protons. This leads to the conclusion that under ordinary conditions, a body is neutral,
i.e. it exhibits no charge.
The above simplified picture of atomic structure shows that matter is electrical in
nature ie. matter contains particles of electricity namiëly, protons and electrons. If the
number of protons is equal to the number of electrons in a body, the resultant charge is zero
and the body willbe electrically neutral. For example, the paper of this bok is electrically
neutral because it has the same number of protons and electrons.
If from a neutral body, some electrons are removed, the protons outnumber the
electrons. Consequently, the body atains a positive charge. Hence, a positively charged
body has deficit of electrons from the normal due share.
If aneutral body is supplied with electrons, then electrons outnumber the protons. As
a result, the body acquires a negative charge. Hence, a negatively charged body has an
excess of electronsfrom the normal due share So, when a body has deficiency or
excess of electrons from normal due share, it is said to be charged or electrified.
How does a glass rod rubbed with silk acquire a positive charge can be explained on
the basis of atomic structure of materials? Electrons farther away from the nucleus are loosely
bound within the atonms. Some of these electrons may be relatively easily removed by
