Voltage divides in series circuit only. In parallel circuit voltage remains same. All of the loads are connected parallelly across voltage source so that loads have two common points with source positive and negative terminals.

Kirchhoff gave two laws for current and voltage. First law is called KCL and second law is called KVL.

**Kirchhoff’s current law (KCL):** This is the first law of Kirchhoff’s about current. How current divide in a circuit this law explains.

American engineer Norton explained his theorem in 1926 after 43 years publishing Thevenin’s theorem. Norton’s theorem is similar to Thevenin’s theorem.

Nortons theorem states that **“a linear two terminal circuit can be replaced by an equivalent current source I _{N} in parallel with a resistance R_{N} where R_{N} is the input or equivalent resistance at the terminals and I_{N} is the short circuit current through the terminals when all the independent sources are turned off”.**

Practically always occurs that a particular element like load is always variable when the other elements are fixed in a circuit. If we consider our household as example a household outlet terminal may be connected to different appliances constituting a variable load. Every time the variable is changed, the complete circuit has to be analyzed again. This is harassment for electrical engineer. To avoid this problem we can use the method of Thevenin’s theorem. The fixed circuit is replaced by an equivalent circuit and according to this method.

An inductor is a passive two terminal element designed to store energy in its magnetic field. Inductor also called reactor or coil. It consists of conductor like wire wound into a coil. When current passing through the coil, energy is stored temporarily into the magnetic field. Applications of inductor in our daily life are transformers, power supplies, TVs, radios, radars etc.

A capacitor is an element which stores charges. It is a passive element as it stores energy. Michael Faraday invented capacitor. The unit of capacitance is Farad was the name of honor of Michael Faraday. In electronics, communication, power systems, computer etc field capacitors are extensively used. In circuit capacitor in an important circuit element, its role can not be described in words.

Linear property is the linear relationship between cause and effect of an element. This property gives linear and nonlinear circuit definition. The property can be applied in various circuit elements. The homogeneity (scaling) property and the additivity property are both the combination of linearity property.

Sometimes we are not sure in electric circuits that the resistors are neither in parallel nor in series.

See the circuit below here the relation between R_{1} resistor and R_{6} resistor is series or parallel we are not sure.