Please explain super position theorem

[togo]

Hi. Here is the paper which we were given an answer to in class but I failed to take it down. I was too busy trying to understand it. What a useless class. Anyways, I am trying to remove all the power sources except for the 40 volt in the middle, but can't tell which direction the currents are supposed to travel.

Because once you determine polarities you add them up algebraically right? Please give me a hand, thanks.

Question #1

**broken link removed**

 

[Ratchit]

togo,

Anyways, I am trying to remove all the power sources except for the 40 volt in the middle, but can't tell which direction the currents are supposed to travel.

Because once you determine polarities you add them up algebraically right? Please give me a hand, thanks.

From your question, I discern that you don't quite understand the principles of superposition, or how to calculate current direction given a voltage polarity. In superposition, you calculate each contribution of each current or voltage, then add them up algebraically. You do not remove the voltage and currents. You set all the current source values and voltage source values except the one you are calculating to zero, and keep the impedances of the voltage sources and current sources. A voltage source has a zero resistance, and a current source has an infinite impedance. You should be able to determine the current direction by the polarity of the voltage sources, and the arrow of the current sources. Try it now. Ratch

 

[MrAl]

Hi,

To add a little to what Ratchit was saying, here is a circuit drawing which might help...

The voltage arrows show the polarity across the resistors, with the tip of the arrow being positive and the tail of the arrow being negative. For a multiple source circuit, this would be after all the other sources have been killed.
You can notice that the voltage arrow for the source points up, so the top is positive, and if you follow the current arrow you'll see that the very first terminal of each resistor becomes positive simply because it connects to the positive of the voltage supply.
This method assumes that we are using the conventional current flow, which is from the positive around the circuit and back to the negative terminal of a source.

The direction of current is assumed, but once the circuit is completely analyzed including all sources the current direction is determined by the result of your equations. This means that during the analysis of each source by itself you might assume a current direction say left to right, but after the analysis it may come out to be actually left to right or right to left, depending on the circuit.