Basics
ELECTRIC CHARGE
"Shocking" Phenomena:
From ancient time to till now, people had came across many “shocking” phenomena, some of them are mentioned below,
Amber effect: Thales of Miletus ($600$ BCE) observed that when amber was rubbed with fur, it could attract light objects.
Lightning: From the ancient times itself, people have been observing the phenomena of lightning. Benjamin Franklin’s kite experiment revealed the fact that lightning was indeed a form of electricity.
St.Elmo’s fire: St. Elmo’s fire is a bright, electrical discharge phenomenon that appears as a glow or sparking, often seen on pointed objects in a ship or aircrafts during thunderstorms.
From "Effluvium" to "Electron":
To explain the above electrical phenomena, Scientists had proposed many theories,
Effluvium: William Gilbert introduced the concept of effluvium (a stream of tiny particles, or a fluid, that flowed from a charged object) in order to explain the amber effect. Few words from his book, “De Magnete”,
An effluvium exhales from amber and is emitted by rubbing: pearls, carnelian, agate, jasper, chalcedony, coral, metals, and other substances of that kind.
Two-fluid theory: Charles du Fay proposed two-fluid theory (Vitreous and Resinous electricity) in order to explain why some rubbed objects attract each other and some repel each other.
Neutral objects have equal amounts of vitreous and resinous fluids. When rubbed, these objects may lose any one of the fluid and become positive or negatively charged.
One-fluid theory: Benjamin Franklin proposed one-fluid theory. According to One-fluid theory, a positively charged object would contain too much fluid, while a negatively charged object would contain too little fluid.
Electron: George Stoney proposed the term “electron” to describe the fundamental unit of electrical charge. Then J.J.Thomson discovered electron. After the discovery of electron, it became easy for the mankind to explain all the electrical related phenomena.
Electric Charge:
Long before the discovery of electron, the concept of charge had been developed and several laws had been formulated.
Hence we still use electric charge as the basic fundamental quantity of electricity.
Electric charge is a fundamental quantity of electricity
Unit: Coulombs (C)
- Charge of an electron = $1.602×10^{-19}\;C$
- Charge of a proton = $1.602×10^{-19}\;C$
From this we can say, $1$ Coulomb of charge equals to $1/1.602×10^{-19}$ number of electrons or protons.
$$1e^{-}=-1.602×10^{-19}\;C$$ $$-1C=\frac{1}{1.602×10^{-19}}e^-$$ $$-1C=6.24×10^{18}\;electrons$$ $$+1C=6.24×10^{18}\;protons$$
Meaning,
- $6.24×10^{18}$ number of electrons constitute $-1$ coulomb of charge
- $6.24×10^{18}$ number of protons constitute $+1$ coulomb of charge
Practice Question (TRB 2006)
Charge of an electron is
a) $1.602×10^{-19}\;C$
b) $-1.602×10^{-19}\;C$
c) $6.24×10^{18}\;C$
d) $-6.24×10^{18}\;C$
Correct Answer: Option B
Charge of an electron is $-1.602×10^{-19}\;C$
As we know, one coulomb of negative charge equals $6.24×10^{18}$ number of electrons. How many number of electrons constitute $n$ coulombs of negative charge?
$$-1C=6.24×10^{18}\;e^-$$
$$-nC=n×6.24×10^{18}\;e^-$$
Practice Question
Which of the following amount of electrons is equivalent to $-3.941\;C$ of charge?
a) $1.628×10^{20}$
b) $1.24×10^{18}$
c) $6.482×10^{17}$
d) $2.46×10^{19}$
Correct Answer: Option D
One coulomb of charge equals
$$-1C=6.24×10^{18}\;e^-$$
‘n’ coulombs of charge equals,$$-nC=n×6.24×10^{18}\;e^-$$
Hence, $-3.941\;C$ equals, $$=3.941×6.24×10^{18}\;e^-$$ $$=24.59×10^{18}\;e^-$$ $$=2.459×10^{19}\;e^-$$
Types of charge:
Positive charge – One coulomb of positive charge equals $6.24×10^{18}$ number of protons.
Negative charge – One coulomb of negative charge equals $6.24×10^{18}$ number of electrons.
Law of Conservation of charges:
Any charge can neither be created nor be destroyed. (i.e) Total charges in a system does not change.
It can only be transferred from one system to another.
