By Squadron Leader Zahid Mir CS&IT Department , Superior University PHY-AP -01 Electric Charge By Squadron Leader Zahid Mir CS&IT Department , Superior University

What is Electric Charge? An intrinsic property of protons and electrons, which make up all matter, is electric charge. Two types of electric charge, positive and negative; a proton has a positive charge, and an electron has a negative charge. The vast amount of charge in an everybody object is usually hidden _ an object contains equal amounts of two kinds of charges.

The total deficiency or excess of electrons in a body is known as its charge.

Charging an Object due to Friction It is possible to transfer electric charge from one object to another. Usually electrons are transferred, and the body that gains electrons acquires an excess of negative charge. The body that loses electrons has an excess of positive charge. Rubbing plastic rod with silk makes plastic negatively charged. Rubbing glass rod with fur makes glass rod positively charged. During any process, the net electric charge of an entire isolated system remains constant (is conserved). This is referred to as the law of conservation of electric charge.

Interaction between charges Charges interact with each other with the help of force of attraction or repulsion between them. Charges can be either positive or negative (Benjamin Franklin 1709 – 1790)

Electrostatics Branch of science which deals with the phenomena associated with charges at rest.

Laws of Electrostatics First Law Like charges of electricity repel each other, whereas unlike charges attract each other. Second Law The force exerted between two point charges is directly proportional to the product of their strength and inversely proportional to the square of the distance between them.

Unit of Charge In SI Units, the unit of charge is Coulomb (C) . 1 C = Charge of 6 x 1018 electrons Charge on 1 electron = 1 = 1.6 x 10-19 C 6 x 1018 Definition of Coulomb One Way In term of electrostatic force : If a charge exerts a force of 1N to another charge at a distance of 1 m apart, then the amount of that charge is 1C. But the force between static charges is difficult to calculate. Other Way In term of magnetic force between current carrying wires.

Quantization of charge Transfer of charge from one object to another is not continuous but in terms of discrete elements. Charges always exists in quantities that are integral multiples of a certain elementary quantity of charge ‘e’. q = ne where e = 1.602 x 10-19 C An electron has a charge of e- Whereas a proton has a charge of e+ Quantization When the value of a property are restricted to discrete multiples of a basic quantity, we say that the property is quantized.

Conductors and Insulators Not only can electric charge exist on an object, but it can also move through an object. Substances that readily conduct electric charge are called electrical conductors. Materials that conduct electric charge poorly are known as electrical insulators. Semiconductors are materials that are intermediate between conductors and insulators

Conductors Why copper rod cannot be charged if you rub it with fur keeping the rod in your hand? Conductors contains a large number of conduction electrons ( 1023 free electrons per cm3).

Insulators In case of charged comb and pieces of paper it is not possible for electrons to collect on one end of paper (as in the case of conductors). Instead electrons in the individual molecules in the bits of paper are repelled by the negatively charged comb and so electrons are partially located on the side of each molecule, that is away from the comb. In each molecule, the positive end is close to comb and feels a greater force of attraction to the comb. Polarization The separation of positive and negative charge in an isolated object under the influence of a nearby charged object is known as Polarization. At macroscopic level it occur in the case of copper rod and at microscopic level in the case of paper pieces.

Charging by Contact and by Induction When we have a pathway through which electrons can flow between an object and the Earth, the object is said to be electrically grounded.