What is the controversy- current and resistance

[i_island0]

http://img339.imageshack.us/my.php?image=controversypo0.jpg

In the above link i have shown a circuit, where in the DC supplies are ideal (i.e. r = 0).
What current will pass through resistance R ,... V1/R or V2/R.

 

[Hootenanny]

Why do you want to know?

 

[algis.j]

You can't divide by 0

 

[Hootenanny]

You can't divide by 0

Although true, totally irrelevant.

 

[mda]

I am guessing (since the image won't load) that you've got two different supplies in parallel with a load resistor?

Essentially you cannot have r=0 exactly... you'd have to take a limiting case which is highly dependent on the details of the power supplies. Examples include known r, limited current, perhaps the supplies cannot sink current etc...

Once you have the non-ideal characteristics of the supplies specified it is reasonably easy to determine the result.

 

[TVP45]

As I understand this, R is not 0; r(internal) is zero and you can do the ideal case without too much worry.

So, what do you know about currents at a junction?

 

[i_island0]

i want to know the current in R.
r is the internal resistance of the batteries, which i have assumed to be zero.

 

[bsimmo]

It is just two cells (power supplies) in parallel to a resistor of value R

The talk about little r confuses things, so just say in the ideal case. Since this is intro physics and a very basic circuit.

Two cells in series (say 2x1.5V, 500mAh types) gives you what current and what voltage if acting as a battery ?
Two cells in parallel (say 2x1.5V, 500mAh types) gives you what current and what voltage if acting as a battery ?

If you cannot answer this basic question, then I suggest picking your the first topic that pops up in google for say 'cells in parallel' and have a read

http://www.batteryuniversity.com/partone-24.htm

 

[i_island0]

ah.. thanks for your answer. .. i m in the process of learning basics only.
In the parallel combination there, both the voltages are same, i.e. 1.2V, so the potential difference is 1.2 V. But if suppose one battery is 1.2 V and other is 1.5 V, then what is the potential difference we should say finally.
The way i have understood is that (1.2 V and 1.5 V ); 1.2 V is a lower voltage, so we will take it will just give low run time, and the final voltage across will be 1.5 V only.

So, for the question that i asked...the current i = max (V1, V2)/R.
If there is something wrong in my understanding, can u please correct me if possible.
thx again

 

[bsimmo]

If you really want to learn, go and do it...

Get yourself some batteries (not mians power supplies), a couple of resistor and voltmeter and ammeter.
Have a play and see what you get.

That should answer your question...

 

[i_island0]

i wish i had that facility with me to experiment. Can you just tell me if i m thinking in the right direction?

 

[Hootenanny]

i wish i had that facility with me to experiment. Can you just tell me if i m thinking in the right direction?

So, for the question that i asked...the current i = max (V1, V2)/R.

Sounds good to me