Combination of resistances and their application to the electrical circuits: The current flowing through a resistor R when connected to the terminals of a voltage source v is given by the Ohm’s law as These resistors often connected with each other in a particular manner and their equivalent resistance need to be calculated using simple formulas in order to calculate current in their respective circuits. Essentially there are two types of combinations are there by which different resistors are connected with each other. They are Series combination of resistors Parallel combination of resistors Series combination: Two or more resistors are said to be in series combination if only one terminal of them are connected to each other. The above figure depicts two resistors R1 and R2 in series combination. The equivalent resistance between the terminal A and B is given by simple addition of the two resistors, i.e., Let the voltage difference between the terminal A and B be V, so the voltage drops at R1 is given And that at R2 is , Where is the current flowing through the circuit. Since the voltage drop is V, we have Or, Thus, the total or equivalent resistance of the circuit is, . If there are more than two resistors, then the equivalent resistance will be Parallel combination: Two or more resistors are said to be in Parallel combination if both of their terminals are connected to each other. The above diagram shows two resistors R1 and R2 in Parallel combination. The equivalent resistance between A and B is calculated here in a different manner. Since both of the resistors sees the same voltage difference as V volt. So, the current through R1 will be , And that through R2 is Now, according to the figure, total current I is Or, . Hence, we get the equivalent resistance in this case as . If there are more than two resistors in the combination as