Solving a SERIES Circuit
When asked to solve a circuit involving resistors in SERIES, we should follow these steps:
a. To find Req, we should use the following equation, adding all values of R:
b. To find IT, we use the following equation, understand that VT is the voltage provided by
the battery/power supply:
c. To determine the current through each individual resistor, we apply the following rule:
d. To determine the voltage drop across each individual resistor, we will use Ohm’s Law,
and use the Resistance and Current appropriate for each resistor:
*For example, we use V1 = I1R1, and for V2 = I2R2, etc. Also, at this point we can make a
simple check to ensure that we are solving the circuit correctly. Applying the following
rule, we can check that our voltage calculations are accurate:
e. To determine the Power for each individual resistor, we will use the following equation,
and use the Voltage and Current appropriate for each resistor:
*For example, we use P1 = I1V1, and for P2 = I2V2, etc. Also, we can make a second
simple check to ensure that we have correctly solved the circuit.
Solving a PARALLEL Circuit
When asked to solve a circuit involving resistors in PARALLEL, we should follow these steps:
a. To find Req, we should use the following equation, using all appropriate values of R:
***Once we have applied this rule, our sum should be a decimal less than one; this is
not our equivalent resistance! To actually find Req, we must invert this decimal, by either
converting it to a fraction (using the MATH￫FRAC function) and then flipping it; or, by
dividing 1 by the decimal.
Ex: if 1/Req = 0.05, we first turn this into a fraction (1/20) and invert (20)
to get Req. Or, we compute 1/0.05 = 20 to get Req.
b. To find IT, we use the following equation, understand that VT is the voltage provided by
the battery/power supply:
c. To determine the voltage drop across each individual resistor, we apply the following
rule:
d. To determine the current each individual resistor, we will use Ohm’s Law, and use the
Resistance and Voltage appropriate for each resistor:
*For example, we use V1 = I1R1, and for V2 = I2R2, etc. Note that the Voltages are equal
to VT, and we are solving for I. Also, at this point we can make a simple check to ensure
that we are solving the circuit correctly. Applying the following rule, we can check that
our Current calculations are accurate:
e. To determine the Power for each individual resistor, we will use the following equation,
and use the Voltage and Current appropriate for each resistor:
*For example, we use P1 = I1V1, and for P2 = I2V2, etc. Also, we can make a second
simple check to ensure that we have correctly solved the circuit.