ELECTRIC CHARGE: A MYSTERIOUS ENTITY
INTRODUCTION
𝒩ature ! full of mysteries but is more interesting to search its mysteriousness .Lightning, Electric sparks, Electrostatic attraction - These all terms are familiar to us.But the thing , we are not familiar with, is the origin of these phenomena means Electric Charge, very serious but interesting topic and is the subject of research . Although its effects have been known to us.Here, we are going to discuss about Electric Charge in a large range.
WHAT IS ELECTRIC CHARGE?
It is an intrinsic property of elementary particles of matter which gives rise to electric force between various objects.SCALAR or VECTOR?
Electric charge is represented by using only magnitude, no direction. So, it is a scalar. It is not a vector.S.I. UNIT
S.I. unit of electric charge is coulomb (C), named after Charles - Augustin de Coulomb.HISTORY
600 BC
- Greek philosopher Thales of Miletus observed that amber(fossilized resin)rubbed with fur attracted light objects.
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1600
- William Gilbert , an English physician, coined the term "electric" from the Greek word for amber (elektron), differentiating it from magnetic phenomena.
1660s
- Otto von Guericke developed the first electrostatic generator, capable of producing sparks.
Ancient and Early Discoveries
1730s
- French scientist Charles-Francois de Cisternay Du Fay discovered two types of electricity, which he called "vitreous" (glass) and "resinous"(amber), noticing that like charges repel and opposite charges attract.
1745-1746
- Ewald Georg von Kleist and Pieter the Leyden jar, the first capacitor used to store charge.
1752
- Benjamin Franklin demonstrated through his kite experiment that lightning is a form of electricity, later proposing that electricity is a single fluid with positive (excess)and negative (deficiency) states.
1785
- French physicist Charles-Augustin de Coulomb published Coulomb's law, which quantitively described the force of attraction or repulsion between charges.
The 18 th Century and Theoretical Understanding
1897
- J.J. Thomson discovered the electron through cathode ray experiments, identifying the fundamental particle responsible for negative charge.
1909
- Robert Millikan's oil-drop experiment determined the charge of a single electron, confirming that electric charge is quantized.
19th Century to Modern Day
POSITIVE AND NEGATIVE CHARGES
- Benzamin Franklin introduced the present day sign convention according to which
- The charge developed on a glass rod when rubbed with silk is called positive charge.
- The charge developed on a plastic/ ebonite rod rubbed with fur is called negative charge
According to this convention , the charge on an electron is negative.
BASIC PROPERTIES OF ELECTRIC CHARGES
Additivity
- The total charge of a system is the algebraic sum of all the individual charges located at different points inside the system.
If a system contains charges q₁, q₂,.....,qₙ ; then its total charge is
Q = q₁ + q₂ +.....+ qₙ Quantisation
- The total charge (Q) of a body is always an integral multiple of a basic quantum of charge (e), which is the charge on an electron.
Q = ± ne
Where n = 0,1,2,3,...... Conservation
- The law of conservation of charge can be stated in a number of ways :
❏ The total charge of an isolated system remains constant.
❏ The electric charges can neither be created nor destroyed, they can only be transferred from one body to another.
➳ Cause of quantization
During rubbing only an integral number of electrons can be transferred from one body to another.
➳ Quantization is experimentally verified
❏ The experimental laws of electrolysis discovered by Faraday first suggested the quantization of electric charge.
❏ Millikan's oil-drop experiment in 1912 on the measurement of electric charge further established the quantization of electric charge.
QUESTIONS WITH ANSWERS
- Is electric charge a basic quantity?
Ans: No, electric charge is not a basic quantity. It is a derived quantity.
- How the electric charge is expressed in terms of basic physical quantities?
Ans: Q = i × t
Here Q = charge( derived quantity)
i = electric current ( basic quantity)
t = time (basic quantity)
- Why electric charge is scalar?
Ans: Electric charge possesses only magnitude. It has no direction. Therefore, electric charge is a scalar.
- Who classified electric charge as positive and negative ?
Ans: Benzamin Franklin
- What field is produced by a charge at rest?
Ans: Electric field
- What field is produced by a charge in motion ?
Ans: Electric field and magnetic field both.
- An ebonite rod is rubbed with wool or fur. What type of charges do they acquire ?
Ans: The ebonite rod acquires a negative charge and fur or wool acqures an equal positive charge.
- A glasse rod is rubbed with silk. What type of charges do they acquire ?
Ans: The glass rod acquires positive charge and silk acquires an equal negative charge.
- Is the mass of a body affected on charging ?
Ans: Yes, electrons have a definite mass. The mass of a body slightly increases if it gains electrons while the mass decreases if the body loses electrons.
- Two identical metallic spheres of exactly equal masses are taken. One is given a positive charge q coulombs and other an equal negative charge. Are their masses equal after charging?
Ans: No, the mass of the negatively charged sphere (excess of electrons) will be slightly more than that of the positively charged sphere ( deficit of electrons).
- A positively charged rod repels a suspended object. Can we conclude that the object is positively charged?
Ans: Yes, the object is positively charged. Repulsion is the surest test of electrification.
- A body A repels another body B, A attracts body C, C repels body D. It is given that body D is positively charged. What is the charge on body B?
Ans: As body C repels positively charged body D, so C is also positively charged .
As body A attracts positively charged body C, so A is negatively charged.
As negatively charged body A repels body B, so body B is negatively charged.
- Name any two basic properties of electric charges.
Ans: Electric charges are
(i) additive
(ii) quantised and
(iii) conserved. - Electrostatic experiments do not work well on hunmid days. Why ?
Ans: Electrostatic experiments require accumulation of charges . Whatever charges appear during the experimentation , they are drained away through humid air which is more conducting than dry air due to the presence of a large number of charged particles in it.
- What does
q₁ + q₂ =0 signify in electrostatic?
Ans: The equation signifies that the electric charges are algebraically additive and here q₁ and q₂ are equal and opposite.
- A polythene piece rubbed with wool is found to have a negative charge of 3.2 × 10⁻⁷ C .
(i) Estimate the number of electrons transferred.
(ii) Is there a transfer of mass from wool to polythene ?