Equivalent Resistance between A and B

In summary: If there are any nonlinearities in the network, then the Rth will not be a perfect 1:1 match between the Vth and PD, and you'll have to adjust the value of Rth to account for these deviations.In summary, when trying to find the equivalent resistance between two points in a circuit, you take into account the power transfer capability of the source and load. If there is a resistor between the two points, it will be ignored when calculating Rth.
  • #1
SpartanG345
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1
Thevenin_equivalent.png

When we are asked to find the equivalent resistance between A and B, i understand we are trying to find the Thevenin resistance between A and B, which is caused by what is in the black box.

However if there is a resistor actually between A and B, do you add this to the Thévenin resistance?

What does the equivalent resistance between 2 points in a circuit mean in a physical sense.
I thought it was the output resistance between 2 points, but if that is the case will a resistor between A and B effect this?
 
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  • #2
To Thevenize a circuit you open all current sources, short all voltage sources, remove the external load and compute the resistance between the output terminals. This gives you the Thevenin resistance. You also need to find the Thevenin voltage. To do this you remove the load and compute the voltage that appears at the output terminals with the all voltage and current sources how they are supposed to be. This is the Thevenin voltage. You then take the Thevenin voltage put it in series with the Thevenin resistance and put that in series with the load. Calculate the current/voltage at the load. You will find those calculated values to be the same as if you solved for the problem conventionally. The advantage to Thevenizing is you can substitute any load in and solve quickly.
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This should answer your question about the resistor in parallel with the output.
 
  • #3
SpartanG345 said:
However if there is a resistor actually between A and B, do you add this to the Thévenin resistance?
No it won't be added to Thevenin resistance, because that resistance will be called as load resistance and has to be removed (not considered) while calculating Rth.
SpartanG345 said:
What does the equivalent resistance between 2 points in a circuit mean in a physical sense.
In a physical sense it implies the power transfer capability of the source Vth to the load at terminal AB. The more the value of Rth, Vth is a weak source as far as load is concerned because a slight current drawn by load, will create more voltage drop across Rth and resulting in less load voltage.
 
  • #4
karthicknar said:
No it won't be added to Thevenin resistance, because that resistance will be called as load resistance and has to be removed (not considered) while calculating Rth.

In a physical sense it implies the power transfer capability of the source Vth to the load at terminal AB. The more the value of Rth, Vth is a weak source as far as load is concerned because a slight current drawn by load, will create more voltage drop across Rth and resulting in less load voltage.

If the resistor between A and B is part of the black box then it is to be figured. Not sure if the OP meant it that way.
 
  • #5
Averagesupernova said:
If the resistor between A and B is part of the black box then it is to be figured. Not sure if the OP meant it that way.
Let me put it this way. Even though I believe there could not be a resistor just between A and B and also a part of black box at same time, let us assume if there is a one, it has to be considered for calculation of Vth and Rth. Yet if that resistance is atleast 100 times larger than load resistance, then it can be safely ignored.
 
  • #6
The basic answer to the question is that any network of resistors, and voltage and current sources will have a, Rth. You can measure this by looking at the change (drop) in PD that you measure when you take various currents into your external load - just like you measure the internal resistance (that you can't get at) of a battery in School.
All that's necessary is for the network to be linear.
 

What is meant by Equivalent Resistance between A and B?

Equivalent Resistance between A and B refers to the total resistance that is experienced by current flowing between two points, A and B, in an electrical circuit. It takes into account all the individual resistances in the circuit and represents them as a single, equivalent resistance.

Why is Equivalent Resistance between A and B important?

Equivalent Resistance between A and B is important because it helps in simplifying complex electrical circuits. By representing multiple resistances as a single equivalent resistance, it makes it easier to calculate the total current and voltage in the circuit.

How is Equivalent Resistance between A and B calculated?

Equivalent Resistance between A and B can be calculated using Ohm's Law, which states that the resistance is equal to the voltage divided by the current. In a series circuit, the equivalent resistance is equal to the sum of all the individual resistances. In a parallel circuit, the equivalent resistance is equal to the reciprocal of the sum of the reciprocals of all the individual resistances.

What factors affect Equivalent Resistance between A and B?

The main factors that affect Equivalent Resistance between A and B are the number and arrangement of resistors in the circuit. In a series circuit, the equivalent resistance increases as more resistors are added. In a parallel circuit, the equivalent resistance decreases as more resistors are added.

What is the unit of measurement for Equivalent Resistance between A and B?

The unit of measurement for Equivalent Resistance between A and B is the ohm (Ω). This unit represents the amount of resistance that restricts the flow of one ampere of current when one volt of potential difference is applied.

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