To find the equivalent resistance of series resistors, we just add up all the individual resistors.
For the circuit in Figure 19.3 , R (^) eq = 3000 Ω. In other words, using three 1000 Ω resistors in series
produces the same total resistance as using one 3000 Ω resistor.
Figure 19.3 Example of series resistors.
Parallel resistors are connected in such a way that you create several paths through which current can
flow. For the resistors to be truly in parallel, the current must split, then immediately come back together.
The equivalent resistance of parallel resistors is found by this formula:
For the circuit in Figure 19.4 , the equivalent resistance is 333 Ω. So hooking up three 1000 Ω resistors in
parallel produces the same total resistance as using one 333 Ω resistor. (Note that the equivalent
resistance of parallel resistors is less than any individual resistor in the parallel combination.)
Figure 19.4 Example of parallel resistors.