BASICS OF ELECTRICAL

ATOMS
All meters (solid, Liquid, Gas) are composed by minute particals called Malicules. There are two part in Atom, 1. Nucleus 2.Extra Nucleus a. Nucleus The Nucleus contains Protons and Neutrons Protons are positively charged particals and Neutrons have no particals b.Extra Nucleus Extra Nucleus contain only Electrons Electrons are negatively charged particals and moves around the Molicules with different orbits. The number of Protons are equels to Number of electrons in an Atom. Atomic Wieght = No. of Protons + No. of Neutrons Atomic Number = No. of Protons or No. of Electrons Normally the Number of Protons and Number of electrons are equles in a body. So the resultant charge is zero and the body electrically neutral. Charge The charge is Electrical energy possessed by protons or Electrons in an Atoms Unlike charges attract each other and like charges or repels each other. The Law of Conservation The Law of Concervation stats the algebraic sum of chares remain constant in a closed path. Therefore the charge can neither be created nor be distorted. The unit of the charge The charge on an electron is so small that is not convenient to select it as the unit charge. Normally Coulomb is the unit of charge. One Coulomb is equal to the charge on 6.28 X electrons. Each protons has positive charge = 1.6 X C. If 6.28 X Electrons remove from a neutral body then the body as positive charge 1 coulomb. If we say that a body has a negative charge of 1 C we should remove 6.28 X electrons from that body. Coulomb Inverse square Law The force two point charges is directly proportional to product of the two charges and inversely proportional to square of distance between two charges. F = 1/4π q1q2/ r - Distance between two charges ε0 – The permittivity of free space ε0 – 8.514 If charge placed in a material then Permittivity = ε0 εr εr – Relative permittivity of the material Electric Field The space around the charge in which the influence is felt is known as Electric field. Electric field Intensity The force experienced by an unit coulomb charge called Electric field Intensity. E = F/q F – Force in Newton q – Charge in Coulomb CURRENT AND VOLTAGE American physicists TOLMAN and STEWART experimentally con formed that the electric current in a conductor is a carried by electrons. The electrons in outer most orbit will less bound with nucleus and called free electrons. The free electrons move at random from one atom to other atom in the materials. Electro Motive Force An external force necessary to move the free electrons in definite direction is called Electro Motive Force. Faradays Law When ever a conductor cut the magnatic field an E.M.F induced in the conductor. E.M.F = BAL sinθ B – Magnatic density in webber A – Area of the conductor L – Length of the conductor. Theory of current (The Machanism of flow of current ) A metal piece contain a large number of free electrons moving in randam directin. The maxiumam speed the free electrons in the order of m/s. Due to e.m.f the electrons get accelerated and move in a definite direction. Due to electric field of moving electrons the electrons in the closed circuit also get accelerated and start to move. The direction of moving electrons can be find by Flamings Right hand rule. If E is the strength of the electric field applied from conductor closed circuit then the force on the electrons in the closed conductor F = e.E e- The charge on electrons in closed circuit. The acceleration produced on on electrons in a closed circuit a = F/m m – Mass of the electrons a = eE / m Due to acceleration the velocity of an electron increase but happens only short time τ. The electrons in a closed circuit contain The additional velocity acquired from e.m.f for τ time is called DRIFT VELOCITY. Vd = a τ =( eE / m) τ. Consider a wire of cross section ‘A’. Let ‘n’ be the number of free electrons per unit volume. The free electrons moves towards left with a constant drift velocity Vd. Numer of free electrons passed through the area of cross section per unit time = nAVd. Therefore the charge that flows per unit time = nAVde. This also called the current flows through the wire I= nAVde. This is relation between current and velocity I= nA E τ/ m. Electric current The rate of follow of charge in any cross section of a wire is defined as the electric current. I = Total charge flowing in a cross section / Time taken If charge dq flows through a wire in small time dt. The electric current = dq / dt. The unit of current is Ampere. One coulomb of charge flow through the wire in one second is called one Ampere. One ampere = 1 coulomb of charge (c) / 1 second (s) = 1 If there is no changes in rate of change of current and rate of change of time the the current is called steady current and if any one or both frequently change then the current called Alternating current .

Theory of Potential different

Consider a body in that one coulomb of negative charge is removed

Now the body is called positively charged body. Certain work was done to charge the body and it is stored in the body as potential energy.