V =0, I=0 , OC or SC?

swayam007

When Voltage across two points is 0 & current flowing through that connection is 0. Is it a short circuit or open circuit?

Studiot

Short circuit means there is zero impedance (resistance) between the two points.
This may lead to zero voltage and no current or a lot of current.

Open circuit means that there is infinite impedance between the two points.
Current flow is always zero but the voltage is indeterminate and may be any value including zero

The condition v=0, I=0 can be either so it is impossible to determine which without knowledge of the connecting impedance.

mistermotown

'When Voltage across two points is 0 & current flowing through that connection is 0'
That means I have an amp meter, and a volt meter. I measure the voltage between two points, and the voltage is zero. I then take my amp meter and measure the current that flows through both those nodes, and that current is zero.

That means your circuit is off buddy, you could just as well have a wire lying on the table, not connected to anything and measure that. You could measure V=0 and I=0 off a glass cup.
:P

If you are talking about circuit theory:
then V=0 is a short circuit AND there can be current flowing through it
I=0 is an open circuit AND there can be a voltage across the two non-connected wires.
But those ONLY count when your circuit is ON in some way.

What are you trying to do? Are you trying to calculate resistance of a circuit, or using super position?

sophiecentaur

If R=V/I and both V and I are zero then you get
R = 0/0
which is indeterminate. You need to specify either V or I.

Ratch

swayam007,

A short or open is determined by physical contact, not by what voltage is across, current through, or resistance between the contacts. So if the contacts physically touch each other, then you have a short circuit across the contacts.

Ratch

sophiecentaur

True but, if all you know is that measurements gave you V=0 and I=0, you cannot determine anything about the resistance - infinite / zero / 347Ω.

Ratch

sophiecentaur,

If you are able to insert an ammeter between the contacts, then you should be able to determine whether they are touching or not, and thereby know whether they are open or closed. The quality of the contacts, such as whether they are dirty or corroded does not mean they are open or shorted. Only a physical inspection can determine that for certain. The resistance of the contacts are a a good indication, but not a certainity of their status.

Ratch

sophiecentaur

According to the title of the thread, your Ammeter reads zero and your voltmeter reads zero. If the only info you have is those readings, then you can tell nothing. You are going for a very practical way of finding out the condition of one particular pair of contacts. Fair enough but unless you have some way of finding current and volts, you can't be sure.

Ratch

sophiecentaur

Well, assuming a perfect ammeter and voltmeter, the ammeter is going to short out the switch so the voltmeter will always read zero whether the switch is open or closed. So, knowing the current and voltage is no sure way to determine the switch status. For me, physical inspection is the definitive determination.

Ratch

sophiecentaur

But who, in their right mind, would ever connect an Ammeter in PARALLEL???

Ratch

sophiecentaur,

[QUOTE]But who, in their right mind, would ever connect an Ammeter in PARALLEL??QUOTE]

I sure wouldn't, but from the OP's description, I envisioned an ammeter in series with the contacts, and a voltmeter across the contacts, both at the same time. That makes the ammeter in parallel with the voltmeter.

Ratch

sophiecentaur

[QUOTE=Ratch;4138194]sophiecentaur,

Are you suggesting that the 'original' circuit consisted of just a loop of wire, joining each of the switch contacts together? What sort of a circuit would that be and what possible use could it be?
I was naturally assuming that the contacts were part of an existing circuit and that they happened to have zero volts across them with no current flowing through them (quite a possibility, in fact it could be part of a balanced bridge circuit, for instance).

Ratch

sophiecentaur,

Nope, I make no assumptions about whether the switch is connected to a circuit or stands alone. All I am saying is that you cannot definitively determine whether the switch is open or closed by just examining the voltage across it or the current through it. A physical examination of the contacts is required to definitively determine whether the switch is open or closed.

Ratch

swayam007

actually It is about a Galvanometer in a balanced wheatstone bridge . Current passing through it & Voltage across it is zero. Is it open circuit or short circuit?

sophiecentaur

So all those 'black box' exercises we did at School and all the measurements done, daily, on components are a waste of time? We have to see what it actually looks like before we can tell the impedance of a circuit element.

Interestingly, it turns out that the scenario was, as I suspected, the situation in a bridge circuit.

Studiot

It is neither open circuit nor short circuit.

I have already outlined the conditions for both and your circuit meets neither.

Note the conditions do not depend on voltage or current.

Ratch

sophiecentaur,

The exercises were theoretical problems. The measurements were determining highly probable conditions. The observation of the contacts are the definitive status.

You can determine the impedance from the theoretical position of the switch, or what you think it is.

Ratch