Circuit Lab/Solving Resistor Circuits

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This is a tutorial page for the event Circuit Lab about solving resistor circuits

The total voltage in the circuit stays the same. Only the voltage used by individual components changes. Here's an example using the formulas for series circuits:

Series Circuits Formulas

Ohm's Law (stated 3 different ways):

[math]E = I \times R[/math]

[math]I = E/R[/math]

[math]R = E/I[/math]

[math]E_{total} = E_{R_1} + E_{R_2}.... + E_{R_n}[/math]

[math]R_{total} = R_1 + R_2.... + R_n[/math]

[math]I_{total} = I_{R_1} = I_{R_2}.... = I_{R_n}[/math]

Circuit 1


To learn everything about this circuit we can use a chart. Start by entering what we know:

Series 1-1.gif

Using the formula: R(total) = R1 + R2.... + Rn we can find the total resistance:

Series 1-2.gif

We can now use Ohm's Law in the form of I = E/R to find the total current in the circuit

Series 1-3.gif

From the formula: I(total) = I(R1) = I(R2).... = I(Rn) we can now determine the current in both resistors:

Series 1-4.gif

Lastly, we can use Ohm's Law E = I x R to find the voltage used by each of the resistors

Series 1-5.gif

Note: Power (P) is measured in Watts (W). The formula is: P = I x E

Circuit 2


In Circuit 2 resistor #1 is increased to 9 ohms with all other parameters remaining the same. Calculate the values for this circuit just as in Circuit 1. Results are:

Series 2.gif

Note: The voltage used by resistor 1 increased and the voltage used by #2, the current and total power decreased.