nortonization of a simple circuit and nodal analysis

[PG1995]

Hi

Please have a look on the following link:
https://img836.imageshack.us/img836/1554/circuitmm.jpg

1: I was trying to solve a circuit. I was successful except the part where I was trying to apply the nodal analysis (it's at the very end of the linked scan). Where am I going wrong? By nodal analysis I get Isc = 1/3 A which is wrong. Where did I go wrong?

2: How would we proceed while applying nodal analysis if the 12V voltage source's polarities are reversed?

It would be very nice of you if you could help me with the above queries. Thanks.

 

[Jony130]

1: I was trying to solve a circuit. I was successful except the part where I was trying to apply the nodal analysis (it's at the very end of the linked scan). Where am I going wrong? By nodal analysis I get Isc = 1/3 A which is wrong. Where did I go wrong?

You write
2A + I - Isc = 0
and
I = (V - 12V)/4Ω but this mean that "I" current is flow form point V toward 12V voltage source.
So you should write like this
I = (12V - V)/4Ω
2 + (12 - V)/4 - V/16 = 0
V ---> 16V---->Isc = 1A

2: How would we proceed while applying nodal analysis if the 12V voltage source's polarities are reversed?

The equation for "I" will be look like this I = (-12V - V)/4Ω

2 + (-12V - V)/4Ω - V/16 = 0

V = -16/5 = -3.2V

 

[PG1995]

Thanks a lot, Jony.