How to check Voltage source or current source in black box?

Thread Starter

wwl17442644

Joined Sep 11, 2019
9
Hi,

There are 2x 2-terminal black boxes, one has a 1V voltage source in series with 1R resistor and another one has 1A current source in parallel with 1R resistor.

How can we know which one is which?

all tools and instruments can be used.

thanks in advance for your help.
WL.
 

ericgibbs

Joined Jan 29, 2010
13,624
hi ww,

Hint:
Remember that an ideal Current source has an infinite source impedance and an ideal Voltage source, zero impedance

E
 

RBR1317

Joined Nov 13, 2010
663
If it is a black box, then you can't know what is inside.

"Black box is a technical term for a device, circuit or a system that is observed in terms of its input, output or transfer characteristics without any knowledge of its internal workings. Black-box modelling usually refers to behavioural modelling of such devices, circuits or systems."
V. Ceperic and A. Baric, "A brief overview of the black-box behavioural modelling of electronic circuits for transient simulations," 2012 Proceedings of the 35th International Convention MIPRO, 2012, pp. 72-77.
 

Thread Starter

wwl17442644

Joined Sep 11, 2019
9
If it is a black box, then you can't know what is inside.

"Black box is a technical term for a device, circuit or a system that is observed in terms of its input, output or transfer characteristics without any knowledge of its internal workings. Black-box modelling usually refers to behavioural modelling of such devices, circuits or systems."
V. Ceperic and A. Baric, "A brief overview of the black-box behavioural modelling of electronic circuits for transient simulations," 2012 Proceedings of the 35th International Convention MIPRO, 2012, pp. 72-77.
where are you from?
 

Sensacell

Joined Jun 19, 2012
2,891
Measure the temperature of the black boxes.

The one with the current source will be dissipating power, while the voltage source containing box will not. (Assuming an open circuit on the output)
 

Ian0

Joined Aug 7, 2020
3,238
Measure the temperature of the black boxes.

The one with the current source will be dissipating power, while the voltage source containing box will not. (Assuming an open circuit on the output)
I wonder if this was the intended answer? Or was the student supposed to say that they were equivalent and it was impossible to tell them apart (electrically) ?
 

dcbingaman

Joined Jun 30, 2021
334
Hi,

There are 2x 2-terminal black boxes, one has a 1V voltage source in series with 1R resistor and another one has 1A current source in parallel with 1R resistor.

How can we know which one is which?

all tools and instruments can be used.

thanks in advance for your help.
WL.
This is a Norton vs Thevenin equivalence. A voltage source in series with a resistor may be replaced with a current source that produces the same voltage in parallel with the resistor. There is no experiment you can perform, nor anything you can connect that will show any difference. Electrically they act the same.
Consider though the voltage source compared to the current source. Which one is consuming power in the box? The only way to tell would be see if heat is being dissipated out of the box. But if it is a true black box. Then no energy can escape from it or enter it. It is a closed system.
 

Thread Starter

wwl17442644

Joined Sep 11, 2019
9
This is a Norton vs Thevenin equivalence. A voltage source in series with a resistor may be replaced with a current source that produces the same voltage in parallel with the resistor. There is no experiment you can perform, nor anything you can connect that will show any difference. Electrically they act the same.
Consider though the voltage source compared to the current source. Which one is consuming power in the box? The only way to tell would be see if heat is being dissipated out of the box. But if it is a true black box. Then no energy can escape from it or enter it. It is a closed system.
Thank you so much man.
 

Ian0

Joined Aug 7, 2020
3,238
This is a Norton vs Thevenin equivalence. A voltage source in series with a resistor may be replaced with a current source that produces the same voltage in parallel with the resistor. There is no experiment you can perform, nor anything you can connect that will show any difference. Electrically they act the same.
Consider though the voltage source compared to the current source. Which one is consuming power in the box? The only way to tell would be see if heat is being dissipated out of the box. But if it is a true black box. Then no energy can escape from it or enter it. It is a closed system.
So the black boxes are not black bodies!
 
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