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I have a question. How do you find total resistance and total current in a bridge circuit or similar circuit?

space scientist wrote:I have a question. How do you find total resistance and total current in a bridge circuit or similar circuit?

There are many ways to do it. My preferred method is to rearrange one side using a delta-wye transform, solve for all the unknowns, and then transform it back. Just make sure you're given enough information first. The delta-wye formulas are here.

ichaelm wrote:

space scientist wrote:I have a question. How do you find total resistance and total current in a bridge circuit or similar circuit?

There are many ways to do it. My preferred method is to rearrange one side using a delta-wye transform, solve for all the unknowns, and then transform it back. Just make sure you're given enough information first. The delta-wye formulas are here.

I don't fully understand the explanation. Please may you explain it a little bit more? In addition, do the formulas work for finding the total current?

space scientist wrote:

ichaelm wrote:

space scientist wrote:I have a question. How do you find total resistance and total current in a bridge circuit or similar circuit?

There are many ways to do it. My preferred method is to rearrange one side using a delta-wye transform, solve for all the unknowns, and then transform it back. Just make sure you're given enough information first. The delta-wye formulas are here.

I don't fully understand the explanation. Please may you explain it a little bit more? In addition, do the formulas work for finding the total current?

Basically, if you take one side of a bridge circuit, you have three resistors that are all connected in a circle - that is, a circuit path goes through R1, R2, and R3 and ends up back at R1 again. That is called a delta formation, because it is like a triangle, or the greek letter delta. You can use the delta-Y formulas to convert a delta formation into a Y formation, which is usually easier to solve. You use the formulas to find a equivalent circuit where instead of having the resistors connected in a triangle, you have resistors of different value connected in a Y formation. The formulas are designed so that the circuit will still work exactly the same way with either formation, with respect to the three nodes involved. Once you convert to a Y, you can solve the circuit and find the total resistance, and given an applied voltage you can find the total current. This will give you a solution for how the whole bridge circuit works with respect to its two ends: the total resistance. If you need to find more specific information about nodes within the bridge circuit, such as the individual voltages across each resistor, then you can convert back to a delta and use the information you just got for the whole circuit to help determine the individual voltages.

There are other ways to solve the circuit, like by using Kepler's voltage law, but I think this is the most systematic for a question on a test. I found an example for you on this webpage

Thank you ichaelm. The information that you posted is useful.

Kepler's voltage law? I think you mean Kirchoff's?

Depending on the circuit you may or may not be able to apply KVL to find what you're looking for.

If not, yeah, apply a delta-wye transform. Then, in the basic bridge circuit, you end up with a simple series-parallel combination you can solve.

Regarding the delta-wye transformation, is that technically covered in the rules? I would consider it covered under general circuit knowledge... Perhaps for a more "difficult" section to differentiate teams. On the same note, do you think KVL and KCL should be considered part of the tests?

Any thoughts from competitors or anyone else?

Hey I'm a little bit confused about the whole 'internal resistance of a battery' concept. Can anybody help me out?