Why is there no current in a parallel branch of a short.

[George317]

its a simple circuit one branch has a resistor and its in parallel with a short

i understand that the short branch has no resistance other than the wire itself which means it has super small resistance and by ohm's law I = V/R where the voltage is divided by a super small value means the current will approach infinity basically super high.

but why does my professor tell me that the other branch have no current? there's indeed a resistance in the short's wire right?, so the voltage in the short is not actually zero via V=IR, and it should be in parallel with the other branch with the resistor hence the 2 branches have the same voltage, and we can see that I = non-zero voltage / resistor = non-zero value.

ty

 

[anorlunda]

You're right and wrong.

When you say that the short has zero resistance yet talk about the nonzero voltage across it, that's wrong.

When you say that the short has a small nonzero resistance, then there will be nonzero current through the parallel resistor, that's right.

If you have unequal nonzero resistances, R1 and R2 in parallel, can you write the expression for the ratio of the currrents between them?

 

[George317]

You're right and wrong.

When you say that the short has zero resistance yet talk about the nonzero voltage across it, that's wrong.

When you say that the short has a small nonzero resistance, then there will be nonzero current through the parallel resistor, that's right.

If you have unequal nonzero resistances, R1 and R2 in parallel, can you write the expression for the ratio of the currrents between them?

i mean the short has no resistance other than the resistance in the wire hence there should be nonzero voltage in it. is this correct?

i think it possible because they have the same voltages for being in parallel so I1 = V/R1 then I2 = V/R2.

basically does that mean that there is indeed a current that exist in the parallel branch of the short circuit? just that its super small?

 

[Averagesupernova]

We need to nail a few things down. What is zero and in what perspective? And how do you want to define a short circuit? A wire with truly zero ohms resistance implies we are working with ideal components. In this case, there would be zero branch current. In the real world where the wire does have a slight resistance, then we will have branch current. So you need to pick your words and definitions very carefully. A wire with .001 ohms is practically zero in one perspective, but in the case of an ammeter shunt, care needs to be taken to keep track of that .001 ohms.
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Off topic, but worth mentioning: I recently had a power supply/battery charger apart. This unit was old school, made to charge lead acid batteries and also had a voltage regulated mode. There was a coil of solid copper wire inside which I am guessing was number 12 or 14. The coil was probably about a half inch diameter and 3 inches long. There were a pair a small stranded wires soldered to this coil. This is a case of requiring branch current to run a moving coil panel meter to indicate current. The voltage drop across this coil was non-zero. In simpler terms, it was a shunt. Quite possibly confusing to a beginner.

 

[CWatters]

George...you are both correct. Your tutor is talking about an ideal short circuit where even the resistance of the wire can be considered zero. You are talking about real wires that do have some resistance. Usually if a problem doesn't mention the resistance of the wire you can ignore it and use the assumption given by your tutor.