A combination circuit has some components linked together in series (one after the other), and others in parallel (on different branches). Look for areas of your diagram that simplify to a single series or parallel section. Circle each one to help you keep track of them.

For example, a circuit has a 1 Ω resistor and a 1.5 Ω resistor connected in series. After the second resistor, the circuit splits into two parallel branches, one with a 5 Ω resistor and the other with a 3 Ω resistor.Circle the two parallel branches to separate them from the rest of the circuit.
 Use the parallel resistance formula 1RT=1R1+1R2+1R3+...1Rn{\displaystyle {\frac {1}{R_{T}}}={\frac {1}{R_{1}}}+{\frac {1}{R_{2}}}+{\frac {1}{R_{3}}}+...{\frac {1}{R_{n}}}} to find the total resistance of a single parallel section of the circuit.

The example circuit has two branches with resistance R1 = 5 Ω and R2 = 3 Ω.1Rparallel=15+13{\displaystyle {\frac {1}{R_{parallel}}}={\frac {1}{5}}+{\frac {1}{3}}}1Rparallel=315+515=3+515=815{\displaystyle {\frac {1}{R_{parallel}}}={\frac {3}{15}}+{\frac {5}{15}}={\frac {3+5}{15}}={\frac {8}{15}}}Rparallel=158=1.875{\displaystyle R_{parallel}={\frac {15}{8}}=1.875}Ω


, Once you've found the total resistance of a parallel section, you can cross out that whole section on your diagram. Treat that area as a single wire with resistance equal to the value you found.

In the example above, you can ignore the two branches and treat them as one resistor with resistance 1.875Ω.
 Once you've replaced each parallel section with a single resistance, your diagram should be a single loop: a series circuit. The total resistance of a series circuit is equal to the sum of all individual resistances, so just add them up to get your answer.

The simplified diagram has a 1 Ω resistor, 1.5 Ω resistor, and the section with 1.875 Ω you just calculated. These are all connected in series, so RT=1+1.5+1.875=4.375{\displaystyle R_{T}=1+1.5+1.875=4.375}Ω.
 If you do not know the resistance in one component of your circuit, look for ways to calculate it. If you know the voltage V and current I across that component, find its resistance using Ohm's Law: R = V / I.
Break down your circuit into series sections and parallel sections.
Find the resistance of each parallel section.
Simplify your diagram.
Add up resistances in series.
Use Ohm's Law to find unknown values.
{"src": "wikihow-all_test", "title": "How to Calculate Total Resistance in Circuits3"}