Problem #1

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I came across this problem in a book and I admit becoming a deer in the headlights 

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I remember looking at the answer and not liking it  though I do not recall

Initially I proposed that current can only flow in one direction and when the cathode end is negative then current will flow.

But the cathode end is also connected to ground  sooooo how's it gonna be negative 

I welcome as usual any advice hints speculation solutions discussion etc

The good news is I'm going to construct this circuit I have a few transformers and can put some low voltage like 6 to 12 volts on the secondary 

I'm still a bit hesitant to ground one terminal of the secondary 

But that's the good thing is i can simply build it and not take chances like have a fuse etc

And that's what I like is I don't have to stare at something for days trying to make sense of it or accept it when I have the components and test equipment to actually see what happens 

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The cathode is not grounded.  Think about how an inductor reacts to AC.
The question is a bit misleading as it implies there will be DC at the cathode, I would not call it exactly that.

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Yes sir thanks 

Ok guys I finally got around to trying to physically reproduce this scenario 

First order of business was (safely) connecting mains to a transformer which was cool because I got some training on three prong plug 🔌 pinout

When I connected to the 120v primaries I got about 28v output so I tried the 240 primary and got a nice 14v output



I took a few pics but I'm told they are too large so IDK if this is something temporary or maybe I can change the settings on my phone.

Anyhow now I just need to solder some breadboard friendly leads on to my secondaries and it's gonna be on 

I tried this pic and I can upload it idk why it's less MB than the others 

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I'm gonna have to think about this one for a while 

I started with multimeter readings and they were crazy 

So time to look with a scope


This is the anode side

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And the cathode side

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Sorry the camera only got partial wave forms

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DC readings

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At least I have a purpose in life now.  To figure out why I'm getting six volts Vf across a diode.
I'm guessing maybe the "DC" on the cathode side is getting cancelled out idk
But it's cool 😎

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So I was wondering about this and now my suspicion is that one of the "secondaries" is a center tap and I should know this but even further perhaps it is grounded.

 


But alas I just tested continuity from each secondary to every primary wire and got nothing 

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Stick with the format of the drawing in the first post.  The way it's drawn in post #4 will just confuse things.
The diode lets the negative alternation of the sinewave through, because of the polarity.  It's a negative pulse and not really DC yet. 
If you put a filter cap across the resistor, it will look more like DC, depending on the value of the cap.  Bigger cap will filter out more ripple.
Remember it's a negative pulse, so + end of cap goes to ground.

A center-tapped secondary would have 3 wires.  No wire on secondary side should ever have continuity to primary side.

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Yes sir thanks so much for helping with this I never thought of the cathode allowing negative voltage to pass      but that makes perfect sense and explains some things 

All this time I expected for some reason the ground waiting for the AC side to be negative then a positive voltage would travel through the resistor and diode.

Also now I imagine that the guy that came up with the problem in this book could have made a simple problem by having the cathode pointed towards the resistor and ground but instead made it more interesting (and challenging)

Also I'm knocking myself upside the head for not using my resources ie dude look at the scope pics it's pretty obvious what is happening