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Electric Charges


Electric charge is a fundamental property of matter. An object can have a positive or negative electric charge, or it can be electrically neutral. The properties of electric charges are:

  1. Like charges repel, opposite charges attract. The force between charges is given by Coulomb's law.
  2. Electric charge is conserved, it cannot be created or destroyed.
  3. Electric charge is quantized, which means that the smallest possible amount of electric charge is the charge of a single electron $e$.

Charge by Friction

Charge by friction is a method of charging an object by rubbing it against another object. When two objects are rubbed together, some electrons can be transferred from one object to the other, resulting in a net charge on each object.


For example, if you rub a glass rod with a piece of silk, the glass rod will acquire a positive charge and the silk will acquire a negative charge.

Charge by Conduction

Charge by conduction is a method of charging an object by allowing it to come into contact with another charged object. When two objects with different charges touch each other, some of the excess charge is transferred from the more highly charged object to the less highly charged object, equalizing the charges on the two objects.


For example, if a negatively charged object (such as a balloon that has been rubbed against a sweater) is brought into contact with an initially neutral object (such as a metal sphere), some of the excess electrons on the balloon will flow onto the metal sphere, creating a negative charge on the sphere. If the metal sphere is then disconnected from the negatively charged balloon, it will retain the negative charge that it acquired through conduction.

Charge by Induction

Charge by induction is a method of charging an object by bringing it near a charged object, without actually making physical contact between the two objects. When a charged object is brought near an uncharged object, the electric field of the charged object can induce a separation of charges within the uncharged object, resulting in a net charge on the object.


The process of charge by induction involves the following steps:

  1. An initially neutral object is brought near a charged object.
  2. The electric field of the charged object causes a separation of charges within the neutral object.
  3. If the neutral object is then connected to a grounding wire or another conductive object, electrons can flow from the negatively charged side of the object to the grounding wire, creating a negative charge on the initially neutral object.
  4. Once the grounding wire is disconnected, the charged object can be removed, leaving the induced charge on the neutral object.


  1. Demos on Electrostatics
  2. Coulomb's law
JEE Physics Solved Problems in Mechanics