 What is the difference between a series and a parallel connection of resistors? Here we consider a series and a parallel circuit with three resistors with resistances R1, R2 and R3. A voltage U is applied to the resistors. Difference number one. Look at how the three resistors are connected to each other. In a series circuit, the positive pole of the voltage source is connected to one single resistor. And the negative pole is also connected to one single resistor. The resistors in a series circuit form a chain. In a parallel circuit, on the other hand, you connect the positive pole of the voltage source to three ends of the three resistors. And you do the same with a negative pole. Difference number two. In a series connection, the same current flows through all three resistors. The total current I is therefore equal to the current I1 through the first resistor, but also equal to the current I2 and I3 through the other two resistors. In a parallel circuit, however, different currents I1, I2 and I3 flow through the resistors. The total current I is the sum of the individual currents. I is equal to I1 plus I2 plus I3. In a series circuit, you will measure a different voltage across each resistor. Voltage U1 across the first resistor, U2 across the second resistor, and U3 across the third. The total voltage U is the sum of the individual voltages. U is equal to U1 plus U2 plus U3. In a parallel circuit, on the other hand, you will measure the same voltage across all three resistors. The total voltage is therefore equal to the voltage U1 between the ends of the first resistor, but also equal to the voltage U2 and U3. Difference number four. The total resistance R of a series circuit is the sum of the individual resistances. R is equal to R1 plus R2 plus R3. In a parallel circuit, however, the total resistance R is not the sum of the individual resistances. The following relationship applies here. The reciprocal total resistance 1 over R is the sum of the reciprocal resistances 1 over R1 plus 1 over R2 plus 1 over R3. Difference number five. For the conductance values of the resistors, it is the other way around. The total conductance G of a parallel circuit is the sum of the individual conductances, G1, G2, and G3. And in a series circuit, the reciprocal conductance 1 over G is equal to 1 over G1 plus 1 over G2 plus 1 over G3.