ELECTROSTATICS

Electrostatics
Branch of science that deals with the study of forces, fields, and potentials arising from the static charges
Electric Charge

• In 600 B.C., the Greek Philosopher Thales observed that amber, when rubbed with wool, acquires the property of attracting objects such as small bits of paper, dry leaves, dust particles, etc.
  
• This kind of electricity developed on objects, when they are rubbed with each other, is called frictional electricity.
  
• The American scientist Benjamin Franklin introduced the concept of positive and negative charges in order to distinguish the two kinds of charges developed on different objects when they are rubbed with each other.
  
• In the table given below, if an object in the first column is rubbed against the object given in second column, then the object in the first column will acquire positive charge while that in second column will acquire negative charge.
  

I	II
Woollen cloth	Rubber shoes
Woollen cloth	Amber
Woollen cloth	Plastic object
Fur	Ebonite rod
Glass rod	Silk cloth

• Electric charge − The additional property of protons and electrons, which gives rise to electric force between them, is called electric charge.
  

Electric charge is a scalar quantity. A proton possesses positive charge while an electron possesses an equal negative charge (where e = 1.6 × 10⁻¹⁹ coulomb).

• Like charges repel each other whereas unlike charges attract each other.
  
• A simple apparatus used to detect charge on a body is the gold-leaf electroscope.
  

Conductors and Insulators
Conductors

• The substances which allow electricity to pass through them easily are called conductors.
  

Example − All the metals are good conductors.

• Conductors have electrons that can move freely inside the material.
  
• When some charge is transferred to a conductor, it readily gets distributed over the entire surface of the conductor.
  
• When a charged body is brought in contact with the earth, all the excess charge on the body disappears by causing a momentary current to pass to the ground through the connecting conductor (such as our body). This process is known as earthing.
  

Insulators

• The substances which do not allow electricity to pass through them easily are called insulators.
  

• Most of the non-metals such as porcelain, wood, nylon, etc. are examples of insulator.
  
• If some charge is put on an insulator, then it stays at the same place.
  

Charging By Induction

A conductor may be charged permanently by induction in the following steps.
Step I

To charge a conductor AB negatively by induction, bring a positively charged glass rod close to it. The end A of the conductor becomes negatively charged while the far end B becomes positively charged. It happens so because when positively charged glass rod is brought near the conductor AB, it attracts the free electrons present in the conductor towards it. As a result, the electron accumulates at the near end A and therefore, this end becomes negatively charged and end B becomes deficient of electrons and acquires positive charge.
Step II

The conductor is now connected to the earth. The positive charges induced will disappear. The negative induced charge on end A of the conductor remains bound to it due to the attractive forces exerted by the positive glass rod.
Step III

The conductor is disconnected from the earth keeping the glass rod still in its position. End A of the conductor continues to hold the negative induced charge.
Step IV

Finally, when the glass rod is removed, the negative induced charge on the near end spreads uniformly over the whole conductor.
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