Electrification - "Electric charges"

Electric charges:

 Historical review of Electrostatics

Science of electrostatic has its origin dated back, about 2600 years. For a long time, the phenomenon remained unexplained. With the development of science, various arguments were put forward to explain it. 

1. The first observation is credited to a Greek philosopher Thales of Miletus (640-540 B.C.) who observed that is 'amber' (hardened sap of a kind of pine tree, a yellow resinous substance found on the shores of Baltic sea) is rubbed with silk or flannel, it acquires the property of attracting straw towards itself. No explanation to this phenomenon could be given at that stage. 
2. About 2000 years after this an English Physicist William Gilbert observed that there were a number of other substances, apart from 'amber' which acquired this property when rubbed. He named this property as 'electric attraction'. The word electric was ascribed to this characteristics because the amber was known as 'electron'. 
3. In 1671, Otto von Guericke discovered the property of electric repulsion when he found that some features moved away from a charged body if allowed to touch and separate. 

Electrification - "Electric Charges"

Science of electrostatics, has its origin dated back to 600 B.C. of course, the name electrostatics was given to it much later. The discovery is credited to a Greek Philosopher Thales of Miletus (600 B.C.). He observed that if amber (a yellow resinous substance found on the shores of Baltic sea) is rubbed with a woollen cloth, it acquires some special properties of attracting small pieces of paper, light features, dust etc. towards it. Same phenomenon is observed in case a glass rod is rubbed with a silk cloth. Even if we test our comb after combing our hair, it is found to show this phenomenon. The amber, the glass rod or the comb is said to have acquired electricity on itself. The word 'electricity' is derived from 'electrum' which is a Greek name of amber. 

These substances tend to show abnormal behaviour due to reason that they have developed some charges upon themselves or in other words they have been electrified. A charge cannot be termed as something physical, i.e. something having shape, size or volume. 

A charge is a fundamental characteristics property of the elementary particle of the mental which is explain certain force of interaction and some type of interaction energy. 

• The word electricity is derived from electrum. 
• Electric charge is scaller quantity. 

William gillbert who did primity ward on electrification. He observed that there are two types of electrification is possible. 

1. One type of electrification is acquired by umber rubbed with wollen clothe. This type of electrification is named as resinous. 
2. Second type of electrification is acquired by a glass rod rubbed with silk. This type of electrification is named as vitreous. 

Latin american scientist Benjamin Franklin named +ve and -ve charge. 

1. Type of charge acquired by a glass rod when rubbed with silk is called +ve charge. 
2. Type of charge acquired by umber when rubbed with woollen cloth is called -ve charge. 

For production of electric charges we need a predestined pair of substances and these have to be rubbed together. As a result of electrification, one substance (of the pair) acquires a positive charge while the other acquires a negative one. Following table gives a number of such pairs along with the nature of charges developed upon them. 

Table:

Sl no.	Pair	Positively charged	Negatively charged
1.	Glass, Silk	Glass	Silk
2.	Cat skin, Ebonite	Cat skin	Ebonite
3.	Flannel, Ebonite	Flannel	Ebonite
4.	Woollen cloth, Amber	Woollen cloth	Amber
5.	Woollen cloth, Rubber	Woollen cloth	Rubber
6.	Woollen cloth, Plastic	Woollen cloth	Plastic
7.	Dry hair, Comb (Plastic)	Dry hair	Comb

Like charges repel and unlike charges attract each other - "Basic law of Electrostatic "

It can be proved that like charges repel each other and unlike charges attract each other. 

Consider two light pith ball pendulums A and B lined with a thin metallic foil and suspended with cotton threads close to each other. 

1) Rub two amber pieces with woollen clothes and touch them with the pendulum. On removing amber it is found that two pendulums get repelled away from each other [Fig. (i)]. This is due to the reason that both of them acquired similar charges. Same observation will be obtained when repeated with glass rods rubbed with silk. 

Electrostatic interaction. 

2) Rub amber with woollen cloth and glass with silk. Touch amber with pendulum A and glass with pendulum B. It will be observed that the two pendulums A and B move towards each other indicating that they attract each other [Fig. (ii)]. This is due to the reason that they had been given opposite type of charges. 

These two experiments also indicate that there are two types of charges produced as a result of rubbing one substance with another. 

Existence of only two types of charges

It can be proved that there is existence of only two types of charges 'positive and negative'. Let the glass, already rubbed with silk, be denoted as a body A while amber, rubbed with woollen cloth, be denoted as a body B. Let 'C' be any other charged body in this universe. Bring 'C' near A and B turn by turn, it will be observed that if C is attracted by A, it will be repelled by B and vice-versa. We cannot find any charged body which is attracted or repelled by A and B simultaneously. If a number of charged bodies are all repelled by A, these bodies are bound to repel each other also. This indicates that the charges on all these bodies belong to one category only and is similar to the charge on A. If a number of charged bodies are repelled by B, they are bound to repel each other also, indicating that they possess charges of one category and that is similar in nature to the charge on B. 

Hence, there is a possibility of only two types of charges, one produced on glass rod when rubbed with silk (called positive) and second on amber when rubbed with woollen cloth (called negative).