Electrostatics

 Electrostatics XI

Charges at Rest

Charges : Every object in the universe is made up of small unit called as atom. Every atom consist of two type of charges viz. (Negatively charged electrons and positively charged Proton) as shown in fig above. This charges has different characteristics depending upon the state of rest and state of motion. When the charges are in motion they constitute electric current and when the charges is at rest it constitute static system. We are going to discuss about characteristics of charges when it is at rest in this chapter.

Try this experiment below

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Electrostatics : The study of charges at rest is called as Electrostatics. We have observed various phenomenon in our daily life (when the comb is rubbed with hair and brought near small pieces of paper, it attracts the paper. This is due to the static charge developed on the comb due to rubbing of comb.

Method of charging an object: There are two method of charging a conductor viz (a) Conduction method  (b) Induction method. Let us understand it in detail.

(A) Conduction method of charging : The method of charging in which charges are developed  on a neutral object due to their interaction (contact)is conduction method of charging. Let us understand it with an example.

Consider two Neutral object A and B .Object A is having 5 electrons and  5 protons as shown in fig above, similarly object B is having 4 charges each. When these object are brought together in contact and rubbed with each other electron are transferred from on object to another a shown in fig below. Let us consider 1 electron from A gets transferred to B, thus the equivalent charges on the body  A is due to only one Proton as effect of 4 electron is cancelled out by 4 protons whereas, The equivalent charge on body B is due to 1 electron as effect of electron is cancelled out by 4 proton. The diagram below is well illustrated to understand the concept.

Thus Body A developed 1 positive charge as it donates electron and body B develops 1 negative charge ad it accept one electron. As this charges are at rest ,the study of such charges are called as electrostatics.

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(B) Induction method of charging : The method of charging in which charges are developed  on a neutral object without their actual interaction (contact) is called as induction method of charging. Let us understand it with an example.

From the figure above we can see that initially, object A is neutral. A negatively  charged body is brought near the body  and as  soon as the charged object is brought near the body A , the negative charges begin to move away due to force of repulsion and positive charge is moved toward it due to force of attraction. If we connect a conductor to the body A and other end of the conductor is connected to earth all the negative charges flows in the earth  and the charges remaining on the body is only positive charges and body is said to be positively charged. The diagram below is well illustrated to understand the concept.

Conductor connected to ground

Induction method

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