Parallel Circuits Click one of the buttons above to move to that topic.
 Your browser does not support Java Applets A circuit with more than one path of current flow is a parallel circuit. VOLTAGE IN PARALLEL CIRCUITS The total voltage is equal to the voltage of any parallel resistance. CURRENT IN PARALLEL CIRCUITS The total current is equal to the sum of the current of each parallel component. RESISTANCE IN PARALLEL CIRCUITS The total resistance can be calculated using ohm’s law if the voltage and total current are known. The total resistance is always less than the lowest value of resistance. Equal-Value Method For parallel resistances in which all resistors are the same value the resistance can be calculated by dividing the value of one of the resistors by the number of resistors. Reciprocal Method For parallel resistances in which all resistors are the same value the resistance can be calculated by dividing the value of one of the resistors by the number of resistors. 1/RT = 1/R1 + 1/R2 + 1/RN REQ = 1 / ( 1/R1 + 1/R2 + ... + 1/RN ) Product-over-the-Sum Method For calculating the resistance of two resistors in parallel this formula may be used: REQ = (R1 * R2) / (R1 + R2) The 10-to-1 Approximation Rule If two resistors are connected in parallel and one resistor is 10 or more times greater in value than the other resistor, the greater value resistor may be ignored. CONDUCTANCE The total conductance is equal to the sum of the conductance of each component. POWER IN PARALLEL CIRCUITS The total power is equal to the sum of the power of each component. (This is the same as with series circuits). Rules for Parallel DC Circuits The same voltage exists across each branch of a parallel circuit and is equal to the source voltage. The current through a parallel branch is inversely proportional to the amount of resistance of the branch. The total current of a parallel circuit is equal to the sum of the individual branch currents of the circuit The equivalent resistance of a parallel circuit is found by the general equation Req = 1 / ( 1/R1 + 1/R2 + … 1/Rn) The total power consumed in a parallel circuit is equal to the sum of the power consumed by the individual resistors.    PARALLEL CIRCUIT ANALYSIS Observe the circuit diagram carefully, or draw one if necessary. Note the given values and the values to be found. Select the appropriate equations to be used in solving for the unknown quantities based on the known quantities. Substitute the known values in the equation you have selected and solve for the unknown value. TROUBLESHOOTING PARALLEL CIRCUITS When an open occurs in a branch of a parallel network the resistance of the branch increases and the total resistance of the circuit increases. This causes a decrease in total current.  A short circuit always results in no current flowing through other branches of the circuit.