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Electric Charges and fields

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.

IPositive | IINegative |

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 and is generally denoted by q. 

* Electric charge is a scalar quantity.

* SI unit of charge is Coulomb ( C )

* A proton possesses positive charge while an electron possesses an equal negative charge (where e = 1.6 × 10−19 coulomb).

The property which differentiates the two kinds of charges is called the polarity of charge.

* Like charges repel each other whereas unlike charges attract each other.

Electroscope

A simple apparatus used to detect charge on a body is the gold-leaf electroscope.

It consists of a vertical metal rod housed in a box, with two thin gold leaves attached to its bottom end.

The gold leaves are extremely thin conducting foils which have low mass per unit area and are flexible, therefore, they respond very quickly to small electrostatics forces.

When a charged object touches the metal knob at the top of the rod, charge flows on to the leaves and they diverge. The degree of divergence is an indicator of the...