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d_vipul • Nov 7, 2010

# Whaat will happen if ...

Hey ,

What will hap if a Voltage source of 2V, a Current source of 1A and a resistor of 2 Ohms connected in parallel..........

Find out the current flowing though 2 Ohm Resistor.......

Regards,
VIPUL
mohit007kumar00 • Nov 7, 2010
Re: What will Happened?????

No current will flow through the resister.
reachrkata • Nov 7, 2010
A current of 1A will flow through the resistor. The voltage drop across the 2 Ohm resistor balances the 2V voltage source and therefore no current is drawn from the voltage source. Only the 1A source supplies all the current to the resistor.

Method of analysis - Superposition theorem.

"Only" in this example, the presence of the voltage source is of no use.

-Karthik
nsiva007 • Nov 26, 2010
Current will be 1A, But i disagree with the previous explanation.. By superposition theorem you have to Open Circuit the Current source and Short Circuit the voltage source one at a time keeping the other intact,Thus here first open the circuit the current source keeping voltage source intact ,now 2v is dropped across 2 ohm R,thus current is 1A,next short the voltage source keeping current source intact,now you all know current will not flow across the 2 ohm resistor...! it will flow in the closed loop with no resistance...! SO here the current source is of no use...! According to superposition theorem...!
reachrkata • Nov 30, 2010
Exactly. But what you need to understand is that, the superposition theorem is just a mathematical method of simplifying analysis of circuits with multiple sources. It does not give the actual physical picture. The actual picture is got when we add the results of the superposition theorem. When you do the same thing at the node where the 2 sources and the resistor join and find the currents at the node, you will see that the current from the voltage source is 0 (adding the results of the superposition theorem). The current from the 1A source of course is 1A and the current into the load is 1A (also by superposition). Therefore it is actually the current source that supplies the load.

In fact thinking intuitively also, a voltage source is something that can source or sink any current, but will maintain the voltage. Similarly also a current source can have any voltage drop across it, but will always supply constant current. Therefore to maintain 2V across the 2Ohm resistor, the complete 1A current from the current source has to go into the 2Ohm only, consequently no current from the voltage source is drawn.

-Karthik
π
nsiva007 • Dec 1, 2010
But this problem depends on current direction also right....! Now consider 2V with + polarity facing up (i can't draw circuits here),consider current in down direction...! By super position theorem current on load here is 1A, but considering what you say the entire current is supplied by current source and thus we have a different current direction.. And kirchoff's law is not satisfied for outer loop containing 2V source and 2 ohm resistance....!
Can you explain this....!

-Siva π
reachrkata • Dec 2, 2010
What you have to realise here is that KVL should not be applied along with Superposition. These are two separate tools of analysis never to be mixed up.
Now, if you apply KVL (note without superposition) to the two loops that you said - Loop 1 with the 2V source and the 2Ohm resistor (say loop current I1) and Loop2 with the !A current source and the 2Ohm resistor (say loop current I2). You will get the following loop equation - I1+I2 = 1A
But we already know that I2 = 1A because it is from the current source. So I1 has to be 0, that is no current is drawn from the voltage souce.

For the example that you gave with the Voltage source positive upwards and the current source direction downwards, when you apply the same principles (superpostion or KVL, but independantly), you will see that the voltage source will give 2A, of which 1A goes through the current source and the remaining 1A through the resistor.

Therefore you see, I never meant that just because a current source is there, it is the dominant source. It all depends on the circuit construction.

-Karthik
aj_onduty • Dec 2, 2010
I am scratching my head and asking myself, isn't someone trying to get his homework done by CE?
nsiva007 • Dec 3, 2010
Cool karthick... you brushed my conceptual clarity...! thanks anyway π

Siva π
d_vipul • Dec 10, 2010

actually i forgot to give you the polarity.........

the current through 2 ohm resistance will be 0 Amp for same polarity and 2 Amp for opposite polarity........

EASY ANALYSIS METHOD:

Just transform the current source and resistance into voltage source and resistance in series......
You will get everything...........

This is a logical question no need to apply THEOREMS........

If you are not satisfied with the answer just do a practical........

Some micro ampere current will flow through the resistance due to the uneven voltages.........

will back again with such questions........
Take Care..........

Regards,
VIPUL
nsiva007 • Dec 11, 2010
Oh...! Cool that you followed the thread.. And hurrayπ i got it right..! But anyway i learnt something from both of you guys...!!
d_vipul • Dec 11, 2010
Thanks dude......

actually I was out of town and was busy in my schedule thats why late to reply........

Sorry for that........

Regards,
VIPUL
nsiva007 • Dec 12, 2010
Neva mind dude π

Regards,
Shiva.