Target Audience: High School Students, College Freshmen and Sophomores, Class 11/12 Students in India preparing for ISC/CBSE and Entrance Examinations like the IITJEE Main or Advanced/AIEEE, and anyone else who needs this Tutorial as a reference!Here's a quick outline of what we'll introduce in this tutorial. The omplete tutorial document (PDF) is provided at the end. Circuit theoryThis tutorial is the first in the series for the course circuit theory. This tutorial has the following contents. :Introduction to Electrical Engineering, DC systems, Kirchhoff’s laws, Capacitance. Electric chargeIn all atoms there exists number of electrons which are very loosely bounded to its nucleus. Such electrons are free to wander when specific forces are applied. If any of these electrons is removed, the atom becomes positively charged. And if excess electrons are added to the atom it becomes positively charged. The total deficiency or addition of electrons in an atom is called its charge. A charged atom is called Ion. An element containing a number of ionized atoms is said to be charged. And accordingly the element consisting of that atom is said to be positively or negatively charged. Electric Current (I)All electrons in an atom have certain potential energy. Given a suitable medium in which to exist, they move freely from one energy level to another when small external effort is applied. And this flow takes place from higher energy level to lower energy level. A negative terminal is higher energy level for electron and lower energy level for proton. Similarly a positive terminal is higher energy level for proton and lower energy for neutron. Electricity is the flow of charge. Conventionally the flow of protons from positive terminal to negative terminal is considered as Electric current. Resistance (R) It is the property of electric circuit resisting or preventing the flow of electrons (current). Due to resistance some electrical energy is lost as heat. It depends on various factors. Unit of resistance is Ohm (Ω) Electromotive force (EMF)It is the voltage generated by a battery and is measured in volts. EMF is not a force but the work done in moving +1 C charge around a circuit. The EMF pushes the electrons through the wires of the circuit. It is denoted by E. Potential difference (V)Potential of a particle at a point is the amount of work done in bringing that particle from infinity position to that point. Hence potential difference between two points is defined as the difference in their potential. And accordingly, there exists either repulsive or attractive force between them which is caused by potential difference. Two like charged particles attract each other and unlike charges repel each other. It is also mmeasured in volts and is denoted by V. Ohm’s lawV= I R where R is the constant and is equal to resistance of the conductor. Ohms law is not applicable for non metallic conductors and for non linear devices. Circuits consisting of two or more resistance connected in series to a source are called series circuits. Two resistances in series carry same amount of current. And the voltage supplied is equal to the sum of the voltage drop across each resistance. Parallel CircuitsCircuits consisting of two or more resistance connected in parallel to a source are called parallel circuits. Two resistances in parallel dissipate same amount of voltage. And the total current given out from the source is equal to the sum of the voltage drop across each resistance. Kirchhoff’s Laws:Kirchhoff’s current law:the total current leaving out that node (junction). This is true for any node in a circuit, no matter how many branches lead into or out of the node. It can also be stated as the algebraic sum of currents entering into a node is zero. Different signs are given to currents going into the junction and out of the junction. Kirchhoff’s voltage law: the Voltage sources acting round the loop. CapacitanceA capacitor stores the energy in form of electrostatic field. It is denoted by C and it is measured in Farads (F). The common form energy storage is parallel plate capacitor. If the charges on the plates are +Q and –Q, V is the voltage between two plates then, C = Q/V. For two capacitors connected in series: The current passing through the circuit is denoted by i. In series connection, voltage changes but current remains the same. For two capacitors connected in parallel: The current passing through C1 is i1 and the current passing through C2 is i2. In a parallel connection, the voltage remains the same, but the current varies. Here are some of the questions solved in this tutorial :Q: Q: Q: Q: Q: Q: efficiency of driving motors is 87% and the cost of electrical energy is 8p/kWh. What is the cost of the energy required to make the train travel 1km? If the train velocity is 80km/h and the supplied a constant voltage of 1.5 kV, determine the supply current. Q:A 220v supply is applied across two resistances 10kΩ and 20kΩ each in series. Find the current in the resistances. Q: Three resistances 8Ω, 4Ω, 2Ω are in series. A current of 1A is flowing through them. Find the voltage across each resistor and also total supply. Q: A 100v supply is applied across two resistances 10 and 20 in parallel. Find the currents through each resistance. And find the effective resistance. Q:Find the total current when two resistances 10 Ω and 20 Ω are connected in series and parallel across a supply of 100 V. Q: Calculate the amount of voltage between points A and B in this circuit. And identify polarities and voltage magnitude at those points. Q: Find the total capacitance when three capacitors of 2, 4 and 8μF are connected in i) series ii) parallel ... and many other interesting questions. Complete Tutorial With Solved Problems :Related Tutorials ( Introduction to Electrical Circuits  DC ) :
