Theravin equivalent resistance/current little help

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In summary, the conversation discusses the process of finding the equivalent resistance and current in a circuit, specifically using the Thevenin method. The discussion also brings up the question of why a 10K resistor is "shorted out" when calculating the Thevenin resistance, and the explanation is that all voltage sources are replaced with short circuits, causing the 10K resistor to have a zero resistance resistor in parallel with it, resulting in a short.
  • #1
asdf12312
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theravin equivalent resistance/current little help!

Homework Statement


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Homework Equations


The Attempt at a Solution



found theravin voltage (=-3.75V) but i have a question about the current. the answer is supposed to be -1mA and i found the only way to get this answer was to ignore the 3mA source and the 5k resistor altogether. is there an explanation for this?? just need slight clarification bcause I'm not very smart :(

also, i have a problem when finding theravin resistance method by turning off all independent sources and solving. is there a way to find it using that method? the resistance is supposed to be V(th)/I(sc)=-3.75V/-0.001A=3.75k ohms. but when i use that method i end up putting 10k and 15k in parallel, to get 6k ohms, and put that in parallel with 5k to get R(th)=2.73k ohm. i know i am doing it wrong, is there a way to get the right value though??
 
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By the way, it's Thevenin, not Theravin. You calculate the Thevenin resistance by shorting out the voltage sources, and opening up the current sources, then calculating the equivalent resistance between a and b. When you do this, the 30V voltage source shorts out the 10K resistor, and you're left with just the 5K resistor in parallel with the 15K resistor. The parallel combination of these two gives 3.75K, as you said.
 
  • #3
hmm...ok. any reason why the 10k resistor gets 'shorted' out? other than its on the far end and not really connected to the other resistors? my teacher never mentioned this so i never knew :P

so if there are two resistors on the left side of a source, and 1 to the right of it, if you short the source all 3 resistors are also??
 
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  • #4
asdf12312 said:
hmm...ok. any reason why the 10k resistor gets 'shorted' out? other than its on the far end and not really connected to the other resistors? my teacher never mentioned this so i never knew :P

so if there are two resistors on the left side of a source, and 1 to the right of it, if you short the source all 3 resistors are also??

Yes, of course. If there's a zero resistance path in parallel with a resistance, the net resistance is zero.
 
  • #5
asdf12312 said:
hmm...ok. any reason why the 10k resistor gets 'shorted' out? other than its on the far end and not really connected to the other resistors? my teacher never mentioned this so i never knew :P

so if there are two resistors on the left side of a source, and 1 to the right of it, if you short the source all 3 resistors are also??

The methodology for calculating the Thevenin resistance is that you replace all voltage sources with short circuits and all current sources with open circuits and then calculate the equivalent resistance. After you do this, the 10K resistor on the left has a short (i.e. a zero resistance resistor) in parallel with it. 10K in parallel with zero is zero, i.e., a short.
 

What is Theravin equivalent resistance?

Theravin equivalent resistance is a concept used in electrical engineering to simplify complex circuits into a single equivalent resistance value. It represents the total resistance that would be experienced by a current if it were flowing through a single resistor instead of the entire circuit.

What is the significance of equivalent resistance in circuit analysis?

Equivalent resistance is useful in circuit analysis because it allows us to calculate the total current flowing through a circuit using Ohm's Law (V=IR). This simplifies the process of analyzing complex circuits and can help us understand the behavior of the circuit as a whole.

How is equivalent resistance calculated?

Equivalent resistance can be calculated in series circuits by simply adding up all the individual resistances, and in parallel circuits by using the formula 1/Req = 1/R1 + 1/R2 + ... + 1/Rn. In more complex circuits, equivalent resistance can be calculated using Kirchhoff's Laws.

What is the difference between equivalent resistance and actual resistance?

Equivalent resistance is a theoretical concept used for simplifying circuit analysis, while actual resistance refers to the physical resistance of a component. Equivalent resistance is often different from actual resistance, especially in parallel circuits where the overall resistance is lower than the individual resistances.

How can Theravin equivalent resistance be used to calculate current?

Using Ohm's Law (V=IR), we can calculate the current in a circuit by dividing the voltage by the equivalent resistance. This is possible because equivalent resistance represents the total resistance that the current will encounter in the circuit.

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