Basic DC Theory BASIC DC CIRCUIT CALCULATIONSWhen any two resistors are unequal in a parallel circuit, it is easier to calculate RT by multiplyingthe two resistances and then dividing the product by the sum, as shown in equation (2-11). Asshown in equation (2-11), this is valid when there are only two resistors in parallel.(2-11)RTR1R2R1R2Example: Find the total resistance of a parallel circuit which has one 12W and one 4Wresistor.RTR1R2R1R2(12)(4)12448163WIn 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 theknown resistor be R and the unknown resistor be Rx.RTRRXRRXCross multiply: RTR + RTRX = RRXTranspose: RRX - RTRX = RTRFactor: RX (R - RT) = RTRSolve for Rx:RXRTRRRTRev. 0 Page 35 ES-02
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business