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

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The discussion centers on the comparison of diode resistance in D.C. versus A.C. It is established that the slope of the I-V characteristics graph for D.C. is lower than that for A.C., indicating that D.C. resistance is higher than A.C. resistance. Participants clarify that before the breakdown voltage, D.C. resistance is indeed greater than A.C. resistance, while after breakdown, the relationship reverses. The importance of analyzing the graph's slope is emphasized as a clear method to understand this concept. Overall, the consensus is that D.C. resistance is generally higher than A.C. resistance, particularly before breakdown.
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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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