Basic DC Theory
BASIC DC CIRCUIT CALCULATIONS
When any two resistors are unequal in a parallel circuit, it is easier to calculate RT by multiplying
the two resistances and then dividing the product by the sum, as shown in equation (2-11). As
shown in equation (2-11), this is valid when there are only two resistors in parallel.
Find the total resistance of a parallel circuit which has one 12W and one 4W
In certain cases involving two resistors in parallel, it is useful to find an unknown resistor, Rx,
to obtain a certain RT. To find the appropriate formula, we start with equation (2-10) and let the
known resistor be R and the unknown resistor be Rx.
RTR + RTRX = RRX
RRX - RTRX = RTR
RX (R - RT) = RTR
Solve for Rx: