This week I finished the NEETS module on direct current. One thing that I learned is that there are multiple formulas that can be used to calculate resistance in a parallel circuit. The first formula being Ohm’s Law (resistance is equal to voltage divided by current, R=V/I). This works to find the resistance, but if there is more than resistor one then you’ll need to find equivalent resistance instead. The reciprocal of equivalent resistance is equal to the addition of the resistor reciprocals (1/REQ = 1/R1 + 1/R2 + 1/R3 +…+ 1/Rn ). Another option if the circuit contains resistors that have the same value, you can calculate resistance by dividing the ohmic value of one of the resistors by the number of resistors (REQ = R/N). This is simple but only works when the resistors are equal.
Another thing I finally understand despite years and multiple explanations from previous professors (sorry Dr Moore), is voltage dividers. A voltage divider is used to provide different voltage levels to a circuit while only using one power source. A voltage divider consists of multiple resistors connected in series that step down the voltage. The way to calculate the value of the resistors needed is to use the 10% rule: the current used in the divider resistor should be approximately 10% of the load current. This is called the bleeder current and is not used in the circuit. Once the divider resistor is calculated, finding the total current and dividing by the voltage will give the ohmic value of the second resistor.