Eddy Current
Senior Member
Why would you ever use Kirchhoff's Law instead of Ohms Law? Is Kirchhoff's Law just to prove Ohms Law or is there a time when you would have to use Kirchhoff's Law and not be able to use Ohms Law?
Are Kirchoffs Law and Ohms Law interchangeable?
- Thread starter Eddy Current
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eHunter
Senior Member
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Which of Kirchhoff's Laws are you referring to?
Eddy Current
Senior Member
kwired
Electron manager
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Though some similarities Kirchoff's Laws focus on different details than Ohm's law.
Both Kirchoff's laws and Ohm's law are necessary to solve voltage/current problems.
Both Kirchoff's laws and Ohm's law are necessary to solve voltage/current problems.
eHunter
Senior Member
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- North Texas & Georgia
Don't forget Thevenin & Norton and their contributions to circuit analysis.
Let us first see the OP has become familiar with Mr.Ohm and Mr.Kirchoff.
zog
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ggunn
PE (Electrical), NABCEP certified
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They are both useful and although there is some overlap in what you can calculate with them, they are not completely interchangeable.
gar
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Eddy Current:
Ohm's law and Kirchhoff's laws are not the same thing, and therefore not interchangeable.
See wiki for definitions.
Ohm's law is about the relationship of voltage and current in an invariant resistor. Actually the original experiment was relative to a conductive wire. Ohm's law relates to the conductivity of a material.
Kirchhoff's laws are about the sum of the voltages around a closed loop, and the sum of the currents at a point. The reason wiki has the reference --- circuit laws.
https://en.wikipedia.org/wiki/Ohm's_law 1825-1827
http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws 1845
https://en.wikipedia.org/wiki/Voltage
Historically this quantity has also been called "tension"[4] and "pressure". Pressure is now obsolete but tension is still used, for example within the phrase "high tension" (HT) which is commonly used in thermionic valve (vacuum tube) based electronics.
https://en.wikipedia.org/wiki/Voltage
.
Eddy Current:
Ohm's law and Kirchhoff's laws are not the same thing, and therefore not interchangeable.
See wiki for definitions.
Ohm's law is about the relationship of voltage and current in an invariant resistor. Actually the original experiment was relative to a conductive wire. Ohm's law relates to the conductivity of a material.
Kirchhoff's laws are about the sum of the voltages around a closed loop, and the sum of the currents at a point. The reason wiki has the reference --- circuit laws.
https://en.wikipedia.org/wiki/Ohm's_law 1825-1827
http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws 1845
https://en.wikipedia.org/wiki/Voltage
Historically this quantity has also been called "tension"[4] and "pressure". Pressure is now obsolete but tension is still used, for example within the phrase "high tension" (HT) which is commonly used in thermionic valve (vacuum tube) based electronics.
https://en.wikipedia.org/wiki/Voltage
.
A theorem is deductive and a law is empirical and proved every time the prescribed conditions are met. I think laws are interchangeable but theorem's are not 100% interchangeable with laws. You could use Kirchoffs Law in place of Ohms Law by not having to use Ohms law to find the current at every point of a series circuit, for example. Actually, one is probably a "prescribed condition" that has to be present in order to declare the other a Law? I think Ohms can exist without Kirchoffs, but Kirchoffs cannot be proven without Ohms law.
Eddy Current
Senior Member
Ok i see now where i would have to use one to use the other but where i could not use just Kirchoffs law on a circuit problem without having to use Ohms Law as well.
Another question is some of the Kirchhoff's examples show two power sources. Can you use Ohms law on a circuit that has two power sources and how is that not back feeding?
Eddy Current
Senior Member
Also in Kirchoffs law the closed circuit will always be broken down to a series circuit right?
kwired
Electron manager
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You must remember that a power source will also have an impedance. Connect a 1.5 volt battery in parallel with a 6 volt battery and no other components and the 1.5 volt battery essentially becomes a load to the 6 volt battery doesn't it?
I would say in most cases this is true, but put two sources in parallel and connect two loads in parallel to those sources and you have a circuit that really has no series component, so I say it is not always the case.
ggunn
PE (Electrical), NABCEP certified
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Kirchoff and Ohm are two tools, like a slotted and a Phillips screwdriver. There are screws that you can deal with only with one or the other, some that are merely easier with one than with the other, and some where you can use either with equal effort. To be effective in dealing with screws in general you need them both in your toolbox.
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Wrong.
That is Thevenin's way of solving a circuit.
In Kirchoff's method, a set of simultaneous equations replace a circuit to solve it.
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eHunter
Senior Member
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- North Texas & Georgia
Mine are multi-use tools.
My phillips can double as a center punch and the straight blade(slotted) does duty as a chisel and sheet metal slitter with the help of some Kliens.
The electrical laws and theorems(tools) of Ohm, Kirchhoff, Thevenin, Norton and Maxwell are all tools to be used creatively in solving for electrical quantities and performing circuit analysis, either separately or in combination.
Generally they are used complementary to each other.
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ggunn
PE (Electrical), NABCEP certified
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- Austin, TX, USA
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- Consulting Electrical Engineer - Photovoltaic Systems
That's what I said, innit?
eHunter
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Some people feel that Ohm's Law is E= I R, while others say thatis just the definition of R and Ohm's Law is the statement that approximately, and for some materials, R is a constant.
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