Circuit Analysis
Circuit Analysis
- Do not search for one formula for the whole diagram. Reduce the circuit in a fixed order.
- Label every current and every p.d. before substituting numbers.
A reliable five-step method
- Mark the two endpoints of every parallel section.
- Combine obvious series and parallel resistors.
- Find the source current, including internal resistance when it is present.
- Find the terminal p.d. or the shared p.d. across a parallel section.
- Use , then Kirchhoff's first or second law for the remaining unknown.
Separate total current from branch current
Worked example
A two-branch network
Across an 8.0 V supply, one branch contains 430 Ω and 240 Ω in series. Its current is . If the source current is 0.030 A, the second branch current is . Its total resistance is . If one resistor in that branch is 210 Ω, the other is about 232 Ω.
Common mistake
The current before a junction is the total current. It is not automatically the current in either branch.
Your turn9702/22/M/J/25 Q6(b)(iv)
The current in a branch is 0.018 A. Calculate the p.d. across a 210 Ω resistor in that branch. [1] (9702/22/M/J/25 Q6)
Show worked answer
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