Question about source transforms

[academi4]

Hi, I have a question about something I encountered while working a problem.

http://img171.imageshack.us/img171/5899/questionnz.jpg

I replaced the voltage source in series with the resistor, with a current source in parallel.

I was expecting the current through the 1M ohm resistor to stay the same. Upon inspection, they are different.

I thought about it for a long time and came up with this explanation, can you please tell me if I am thinking correctly:

1.) The resistor and current or voltage source pair can have stuff change in them, but if you draw a box around them, then the output voltage and current to the rest of the circuit is the same.

2.) Since the current through that resistor changes, the power it absorbs changes. However, I suspect:

total power absorbed by 1M ohm resistor + current source = total power absorbed by 1M ohm resistor + voltage source.

Is that correct?

Thanks.

 

[vk6kro]

The two power sources (to the left of the 470K resistor) are equivalent.
They will deliver 9 volts open circuit and 9 microamps short circuit.

The actual current depends on the rest of the circuit.

 

[oswaler]

Hi there,

Thank you for your question. It seems like you are working on a circuit problem and have encountered some unexpected results when replacing a voltage source with a current source. Your explanation is on the right track, but let me provide some additional clarification.

First, let's talk about source transforms. When you replace a voltage source in series with a resistor with a current source in parallel, you are essentially transforming the circuit from a voltage source-resistor combination to a current source-resistor combination. This is known as a source transformation and is a common technique used in circuit analysis.

Now, let's address your first point. When you draw a box around the resistor and the source, you are essentially creating a subcircuit. In this subcircuit, the current and voltage will be the same as in the original circuit. However, when looking at the overall circuit, the current and voltage may not be the same due to the source transformation.

Your second point is also correct. The power absorbed by the 1M ohm resistor and the source will be the same in both the original and transformed circuit. However, the power absorbed by the resistor alone may be different due to the change in current.

I hope this helps to clarify your understanding. Keep up the good work with your circuit analysis! Let me know if you have any further questions.