Resistors are said to be connected in series, when they are daisy chained together in a single line. The current in a series circuit goes through every component in the circuit. Therefore, all of the components in a series connection carry the same current. There is only one path in a series circuit in which the current can flow. As the resistors are connected together in series the same current passes through each resistor in the chain and the total resistance, RT of the circuit must be equal to the sum of all the individual resistors added together.
RT = R1 + R2 + R3……Rn
A series circuits main disadvantage or advantage, depending on its intended role in a products overall design, is that because there is only one path in which its current can flow, opening or breaking a series circuit at any point causes the entire circuit to open or stop operating. For example, if even one of the light bulbs in an older style string of christmas tree lights burns out or is removed, the entire string becomes inoperable until the bulb is replaced.