# need help with this superposition circuit question

#### samson1995

Joined Dec 13, 2016
3
i am supposed to find the current going through R1 using superposition ( supposed to assume the internal resistance of both sources to be 0 ohm).
thanks

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#### RBR1317

Joined Nov 13, 2010
563
Is guessing the value of the unknown resistor supposed to be a part of the problem?

#### samson1995

Joined Dec 13, 2016
3
Is guessing the value of the unknown resistor supposed to be a part of the problem?
no sorry, that should be 2k aswell

#### RBR1317

Joined Nov 13, 2010
563
Great! Now, can you describe the procedure for doing a superposition calculation? Then the next step is to follow the procedure just described.

Note - You can quote the procedure from your textbook. I'll quote the procedure from the following source:

Eliminate all but one source of power within a network at a time, using series/parallel analysis to determine voltage drops (and/or currents) within the modified network for each power source separately. Then, once voltage drops and/or currents have been determined for each power source working separately, the values are all “superimposed” on top of each other (added algebraically) to find the actual voltage drops/currents with all sources active. When re-drawing the circuit for series/parallel analysis with one source, all other voltage sources are replaced by wires (shorts), and all current sources with open circuits (breaks).

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#### samson1995

Joined Dec 13, 2016
3
Great! Now, can you describe the procedure for doing a superposition calculation? Then the next step is to follow the procedure just described.

Note - You can quote the procedure from your textbook. I'll quote the procedure from the following source:

Eliminate all but one source of power within a network at a time, using series/parallel analysis to determine voltage drops (and/or currents) within the modified network for each power source separately. Then, once voltage drops and/or currents have been determined for each power source working separately, the values are all “superimposed” on top of each other (added algebraically) to find the actual voltage drops/currents with all sources active. When re-drawing the circuit for series/parallel analysis with one source, all other voltage sources are replaced by wires (shorts), and all current sources with open circuits (breaks).
just confused about the way current would travel, would it also go through the 2k resistor if we are only examine the source on the right

#### RBR1317

Joined Nov 13, 2010
563
would it also go through the 2k resistor
Of course, the current (or some part of it) would go through all the 2K resistors.

#### MrAl

Joined Jun 17, 2014
7,806
just confused about the way current would travel, would it also go through the 2k resistor if we are only examine the source on the right
Hi,

When you use superposition you short out one voltage source at a time. That represents a topological change in the circuit so current may or may not flow through any given resistor depending on the node voltages on the two terminals.
So at first you may find it easier to see how it works if you redraw the circuit with one voltage source shorted out completely, and then you will get some idea what is going on with the current, but rather than guess what it is just calculate it as you do for a circuit with just one source.

You make one new circuit each time you short out a voltage source, so it is just like analyzing two circuits instead of one, but you sum the results from 'both' new circuits.