1
\$\begingroup\$

enter image description here

In the figure we are supposed to find the current in 8ohm resistor. So by using simple KVL rule I was able to figure it out to be -1.25A.

But in the second approach enter image description here

When I calculated current in 8 ohm resistor, it turned out to be 5.25A. So which answer should I report? And why is there difference in answer I changed the approach?

\$\endgroup\$
8
  • 1
    \$\begingroup\$ How can we know where you went wrong if you don't show your work? \$\endgroup\$
    – Mattman944
    Sep 26 at 14:28
  • \$\begingroup\$ The answer is correct as it is self evident that the potential difference across the branch 32V and 8ohm resistor is 42 volts, and also in the second case it is 42 volts across 8ohm resistor. Also across 24ohm and 14 ohm resistor current was found to be 1.75A and 3A respectively, in both the methods. \$\endgroup\$
    – Preet
    Sep 26 at 14:35
  • 1
    \$\begingroup\$ The voltage "appears" across the resistor. Not the current. The current can only flow through that resistor. Also, why do you think that these currents should be equal? \$\endgroup\$
    – G36
    Sep 26 at 14:36
  • \$\begingroup\$ Because it's the same resistor and we have only transformed voltage source to current source, so there should not be any difference in current in the resistor. \$\endgroup\$
    – Preet
    Sep 26 at 14:38
  • 1
    \$\begingroup\$ The full link to the online simulator is too long. But never mind. As I said only the right part of a circuit will see unchanged voltages and currents. But this is not true for elements that were transformed. Besides, you proved it to yourself by doing this exercise. \$\endgroup\$
    – G36
    Sep 26 at 15:04

2 Answers 2

Reset to default
3
\$\begingroup\$

I1 and r1 are transformations of E1 and R1. R1 is not r1. Only the terminal characteristics are the same. The R1 current in the second figure is shown by the red arrow below

enter image description here

\$\endgroup\$
2
  • \$\begingroup\$ Okay understood! But then what is the significance of current in r1 which was coming out to be 5.25A. \$\endgroup\$
    – Preet
    Sep 26 at 15:48
  • 1
    \$\begingroup\$ The current in r1 is the resistor current for the Norton equivalent. It has no special significance \$\endgroup\$
    – user28910
    Sep 26 at 18:59
3
\$\begingroup\$

The second circuit uses a source transformation to create an equivalent source and resistor output at the terminals. The answers should be different, as it changes the source and resistor.The transformation makes it so that when looking through the terminals, everything will appear the same for the rest of the circuit. I think the idea here is to use the source transformation to solve the right side of the circuit, and then you can go back and solve the original circuit without doing much analysis. Refer to the pictures to see terminals. enter image description here

enter image description here

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.