Is the Resistance of a Diode Higher in D.C. or A.C.?

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    Diode Resistance
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Homework Help Overview

The discussion revolves around the resistance of a diode when subjected to direct current (D.C.) versus alternating current (A.C.), focusing on the interpretation of I-V characteristics and the implications of slope on resistance values.

Discussion Character

  • Conceptual clarification, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the relationship between the slope of the I-V curve and the corresponding resistance for D.C. and A.C. They explore whether the D.C. resistance is greater than A.C. resistance and question the behavior of resistance in different quadrants of the I-V curve.

Discussion Status

There is an ongoing exploration of the relationship between D.C. and A.C. resistance, with participants providing insights based on graphical interpretations. Some participants express uncertainty and seek clarification, while others assert their understanding of the resistance behavior.

Contextual Notes

Participants are considering the effects of reverse bias and breakdown voltage on resistance, which introduces additional complexity to the discussion. There is also a mention of the definition of linear devices in relation to the problem context.

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Homework Statement


upload_2017-9-14_20-48-18.png


Homework Equations

The Attempt at a Solution


Considering I- V characteristics graph, the slope for D.C. resistance is lower than that of the A.C. resistance. Now, the resistance is inverse of the corresponding slope. So, D.C. resistance should be more than A.C. resistance.
 
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Pushoam said:

Homework Statement


View attachment 211098

Homework Equations

The Attempt at a Solution


Considering I- V characteristics graph, the slope for D.C. resistance is lower than that of the A.C. resistance. Now, the resistance is inverse of the corresponding slope. So, D.C. resistance should be more than A.C. resistance.
Can you show us on the I-V curve? I think I know what the answer is, but I'm not sure.
 
berkeman said:
Can you show us on the I-V curve? I think I know what the answer is, but I'm not sure.
upload_2017-9-14_22-5-59.png

It is clear that the slope for D.C. is lower than that for A.C.
Hence, the resistance for the D.C.is greater than that for A.C.
Right?
 

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Pushoam said:
Hence, the resistance for the D.C.is greater than that for A.C.
Yes, correct. With that graph you can show that the tangent to the graph always has a greater slope than the line from the origin to the point on the graph (at least in the 1st quadrant).

Quiz Question -- is it still true in the 3rd quadrant for reverse bias? Include low-level reverse bias and as the diode starts to go into reverse breakdown... :smile:
 
berkeman said:
Quiz Question -- is it still true in the 3rd quadrant for reverse bias? Include low-level reverse bias and as the diode starts to go into reverse breakdown... :smile:
Before the breakdown voltage, the DC resistance is less than AC resistance.
After the breakdown voltage, the DC resistance is more than the AC resistance.
 
Is the definition of linear device following?
Those devices who follow the rule V = IR, are known as linear devices.
 
Pushoam said:
Before the breakdown voltage, the DC resistance is less than AC resistance.
Can you show on the I-V curve why you think this is true? :smile:
 
berkeman said:
Can you show on the I-V curve why you think this is true? :smile:
upload_2017-9-14_23-2-40.png

Sorry, even before breakdown, the slope of AC is more than that of DC.
So, AC resistance is smaller than the DC resistance.

So, DC resistance is always more than the AC resistance. Right?
 
Pushoam said:
So, DC resistance is always more than the AC resistance. Right?
Yep! Good job. Looking at the slope really helps on this type of question. You can also show it mathematically by taking the first derivative of the Diode Equation, but this one is pretty easy to see graphically. :smile:
 
  • #10
:smile::smile::smile::smile:
Done!
Thank you, thanks a lot for guiding me.
 

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