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CHAPTER 1
Electric charges and field
Electric Charge
It is an intrinsic property of the elementary particles like electrons, protons, etc., of which all
the objects are made up of. Electric charge gives rise to electric force between various objects.
It is a scalar quantity. Its SI unit is Coulomb (C). A proton has a positive charge and an
electron has a negative charge , where
coulomb
Electrostatics
It is the study of electric charges at rest. Here we study the forces, fields and potentials
associated with static charges.
Applications of electrostatics
1. In electrostatic loudspeaker.
2. In electrostatic spraying of paints and powder coating.
3. In fly ash collection in chimneys
4. In a Xerox copying machine.
Two kinds of electric charge
About 100 years ago, Charles Du Fay of France showed that electric charges on various objects
are of only two kinds. The following simple experiments prove this fact
Experiment 1
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,(i) Rub a glass rod with silk and suspend it from a rigid support by means of a silk
thread. Bring another similarly charges rod near it. The two rods repel each other.
(ii) Bring a plastic rod rubbed with wool near the charged glass rod. The two rods attract
each other.
(iii) Now rub a plastic rod with wool and suspend it from a rigid support. Bring another
similarly charges elastic rod near it. There will be repulsion between the two rods.
Experiment 2
If a glass rod, rubbed with silk, is made to touch two small pith balls which are suspended
by silk threads, then the two balls repel each other, as shown in Fig. Similarly two pith balls
touched with a plastic rod rubbed with fur are found to repel each other Fig. But it is seen
that a pith ball touched with glass rod attracts another pith ball touched with a plastic rod
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, From the above experiments, we note that charge produced on a glass rod is different from
that on plastic rod. Also the charge produced on pith ball touched with glass rod is different
from the charge produced on pith ball touched with a plastic rod. We can conclude that:
(i) There are two kinds of electric charges – positive and negative.
(ii) Like charges repel and unlike charges attract each other.
The statement (ii) is known as the fundamental law of electrostatics.
Vitreous and resinous charges: Charles Du Fay used the terms Vitreous and resinous for
the two kinds of charges which was replaced by the terms positive and negative charges
respectively, given by Benjamin Franklin (An American pioneer of electrostatics)
1. The charge developed on a glass rod when rubbed with silk is called positive or
vitreous charge.
2. The charge developed on a plastic rod when rubbed with wool is called negative
or resinous charge.
For More Support Download Arvind Academy app (it is free) http://bit.ly/2kTWbkj
Website
YouTube Channel Arvind Academy link http://bit.ly/2lYvJGF
Mobile App Arvind Academy (Android) http://bit.ly/2kTWbkj
Website Arvind Academy https://www.arvindacademy.com
CHAPTER 1
Electric charges and field
Electric Charge
It is an intrinsic property of the elementary particles like electrons, protons, etc., of which all
the objects are made up of. Electric charge gives rise to electric force between various objects.
It is a scalar quantity. Its SI unit is Coulomb (C). A proton has a positive charge and an
electron has a negative charge , where
coulomb
Electrostatics
It is the study of electric charges at rest. Here we study the forces, fields and potentials
associated with static charges.
Applications of electrostatics
1. In electrostatic loudspeaker.
2. In electrostatic spraying of paints and powder coating.
3. In fly ash collection in chimneys
4. In a Xerox copying machine.
Two kinds of electric charge
About 100 years ago, Charles Du Fay of France showed that electric charges on various objects
are of only two kinds. The following simple experiments prove this fact
Experiment 1
For More Support Download Arvind Academy app (it is free) http://bit.ly/2kTWbkj
,(i) Rub a glass rod with silk and suspend it from a rigid support by means of a silk
thread. Bring another similarly charges rod near it. The two rods repel each other.
(ii) Bring a plastic rod rubbed with wool near the charged glass rod. The two rods attract
each other.
(iii) Now rub a plastic rod with wool and suspend it from a rigid support. Bring another
similarly charges elastic rod near it. There will be repulsion between the two rods.
Experiment 2
If a glass rod, rubbed with silk, is made to touch two small pith balls which are suspended
by silk threads, then the two balls repel each other, as shown in Fig. Similarly two pith balls
touched with a plastic rod rubbed with fur are found to repel each other Fig. But it is seen
that a pith ball touched with glass rod attracts another pith ball touched with a plastic rod
For More Support Download Arvind Academy app (it is free) http://bit.ly/2kTWbkj
, From the above experiments, we note that charge produced on a glass rod is different from
that on plastic rod. Also the charge produced on pith ball touched with glass rod is different
from the charge produced on pith ball touched with a plastic rod. We can conclude that:
(i) There are two kinds of electric charges – positive and negative.
(ii) Like charges repel and unlike charges attract each other.
The statement (ii) is known as the fundamental law of electrostatics.
Vitreous and resinous charges: Charles Du Fay used the terms Vitreous and resinous for
the two kinds of charges which was replaced by the terms positive and negative charges
respectively, given by Benjamin Franklin (An American pioneer of electrostatics)
1. The charge developed on a glass rod when rubbed with silk is called positive or
vitreous charge.
2. The charge developed on a plastic rod when rubbed with wool is called negative
or resinous charge.
For More Support Download Arvind Academy app (it is free) http://bit.ly/2kTWbkj
