Question

If the source of a circuit is an ideal current source, and if i open the circuit. what will the current be? Will there still be current flowing? ?

Answer 1

A current has to go from a positive to negative. If you open the circuit, you are cutting off the flow and there's no where the current can flow, so it stops. So to fix that, you just close the circuit again.

Answer 2

doesn't matter it is ideal or not.....to flow a current a closed path is required (lightning is exceptional case where path is air) so in an open circuit no current flows...

Answer 3

As @ghazi mentioned, as long as your voltage is not high enough to cause ionization of air, your current will stop flowing. That is to say, the net movement of charge (from electrons moving in the direction of higher electric potential) within the wire will balance out to 0.

Answer 4

I don't think lightning is that exceptional at all. The circuit resistance is just a lot higher (air is a poor conductor) and therefore much higher voltages are needed to overcome it. I guess it depends on how you look at it...typically a circuit with that high of a resistance is effectively considered open.

Answer 5

Well, @Shane_B , unless you reach the threshold voltage for ionization of air, no (or extremely minimal) current will pass through it. The point is it's not ohmic.

Answer 6

I over-simplified it (or maybe misspoke) but I do agree with you. Once the ionization begins the air will essentially act as a good conductor until the potentials fall back below that threshold.

Answer 7

Hi thanks for the response, the reason i wanted to ask is that. Alright, the definition of ideal current source is that it prescribes a constant current regardless of the voltage or the resistance in the circuit and the voltage of elements will be dependent on the circuit arrange arrangement.

So, let s say, we have an ideal current source(super-duper ideal one), and we open the circuit(even though the circuit is open, it is nothing more than just adding an huge amount of resistance to the whole circuit).. Wouldnt the current source make it such that the voltage across the open part so huge that ionisation occurs and current of the prescribed current flows through it.

Because it is called an ideal current source... That is something confusing me here. Would the current stop or carry flow, because the question mentions this word called IDEAL.

thanks

Answer 8

and sorry for some grammar mistakes there : O

Answer 9

well current ideal current source means ..it will provide you constant current regardless of variation in any factor over which flow of current depends....but this ideal source has absolutely nothing to do with ionisation....for ionisation of air you need a very high POTENTIAL difference .....current source can't help you to figure this out...

Answer 10

yes, we always define v = ir, which gives us the impression that with voltage across a resistance, a current is produced.

But we can write the formula in this, i x r = v. THat means, with current flowing and when it encounters a reistance, it gives rise to voltage?

So, wouldnt the ideal current gives rise to the huge voltage across this huge resistance by ohm's law?

....

i got to check more books. :( anyway thanks alot guys

Answer 11

well first of all ohm's law is valid for a constant temperature only...with increase in current generated heat increases(heat dissipated through resistor ) and hence temperature.....and the very basic condition for a current to flow is potential difference ..when there will be a potential difference then only current will flow...it's not like flow of current causes potential difference ....so doesn't matter amount of current is 10000 Ampere or more than that..first condition is potential difference....and that amount of current can't help to build potential difference.. :) hope that helps you

Answer 12

hi really appreciate that info, how do i give medals btw?

Answer 13

it's fine...at least you got to know a bit of fundamentals.... :)

Answer 14

Also, I think we may be missing a bit of information here. If we're really getting into "ideals" then we should technically be having this circuit in a vacuum. To my knowledge, electrons can't move through vacuum (assuming we're talking classical here)

Answer 15

@vf321: Electrons can certainly travel in a vacuum.

Answer 16

1.-Being ideal or not makes a difference. If it is not ideal, the current of the source will flow through the internal resistance, which in case of current sources happens to be in parallel, thus the voltage will be V=IR (would be the same case for a voltage source, if we make a short circuit, all the voltage is applied to its internal resistance and the current will be I=V/R) 2.-In the ideal case, there is no internal resistance (better, the internal resistance is infinite) and the concept of open current source is as preposterous as a short in an ideal voltage source. An open current source is simply a current that does not exist. A shorted voltage source is simply a voltage that does not exist 3.-Now imagine you have an ideal current source (you will never have one in real life, by the way) and you have a resistor of a very high value connected to it. Voltage will follow Ohm's Law. And it can be as high as you want but again, it is an ideal (theoretical) assumption 4)Have a look at Norton and Thevenin equivalent circuits for a better understanding

Answer 17

@CarlosGP how come voltage flows?? in your third last line??

Answer 18

@ShaneB I meant as in, if you have a capacitor in space, electrons will not magically flow from one side to the other, since the nuclei of the metal atoms that make up the capacitor will hold the electrons much more strongly.

Answer 19

@ghazi I heve never said voltage "flows". The concept of voltage flow does not exist as it is a scalar, in any case the gradient but then we would be speaking about the Electric Field. I say voltage follows Ohm's Law (maybe "flows" and "follows" are similar phonetically but different conceptually )