In the third picture, Do I mark the dots correctly? If the current enter the 1 terminal the positive terminal is 4 terminal.

 

No, move the dot from N 4 to N 3

 

Why did you place them where you did? What was your reasoning?

 

No, move the dot from N 4 to N 3

Why

 

The N3-N4 winding looks quite loose, move it around the core until it fits over N1-N2. Then does it look right?

 

Why

I asked you first.

 

I asked you first.

You read the practice problem

 

How do you expect us to explain why your answer is wrong if you cannot (or will not) explain how you got it? For all we know, you think the dots go on the rightmost terminal of each winding.

And, apparently, you did not read the question since it asked you to show the two correct positions of the two dots and you showed only one. Where is the second answer?

 

How do you expect us to explain why your answer is wrong if you cannot (or will not) explain how you got it? For all we know, you think the dots go on the rightmost terminal of each winding.

From what I learn, dots show polarity of windings, If current enters one dotted terminal , then the dotted terminal of the other winding will be positive or we can say current goes out the dotted terminal of the other winding.

 

How does that my question? Why you place the dots where you did.

 

How do you expect us to explain why your answer is wrong if you cannot (or will not) explain how you got it? For all we know, you think the dots go on the rightmost terminal of each winding.

And, apparently, you did not read the question since it asked you to show the two correct positions of the two dots and you showed only one. Where is the second answer?

one is enough, step by step, if current enters all 1st terminal.s

 

How does that my question? Why you place the dots where you did.

are you a professor or an expert about this?

 

Sorry, I am done. I tried to help but you are clearly not receptive.

 

I have never found it useful to explain the dot convention in terms of current flow. I find it much more helpful to think of it in terms of voltages and phase, or in terms of direction of windings, as do @crutschow and @KeithWalker in the previous thread on this subject.
https://forum.allaboutcircuits.com/threads/transformer-dot-convention-question.177347/

are you a professor or an expert about this?

@BobTPH is an expert.

 

No, move the dot from N 4 to N 3

This E1 is the induced emf, as per definition an induced emf has opposite polarity with current causes it, why in this picture, E1 has the same polarities with V1?

 

hi linhvn,
This image may help
E

 

This E1 is the induced emf, as per definition an induced emf has opposite polarity with current causes it, why in this picture, E1 has the same polarities with V1?
View attachment 339613

Everything is OK with the picture. E1 and V1 are of same magnitude ( roughly the same) as Resistance R1 is relatively small and Leakage inductance Xj is small , too.

There's a simple test to check the polarity of the transformer windings. Connect a centre zero moving coil meter to the secondary winding, positive terminal to the dot marked transformer terminal. Take a battery of 3-6 Volt and connect it to the primary winding, positive terminal to the dot marked terminal. Watch which way the arrow deflects, it should deflect to the right. If it not, the winding marking is wrong

 

Everything is OK with the picture. E1 and V1 are of same magnitude ( roughly the same) as Resistance R1 is relatively small and Leakage inductance Xj is small , too.

There's a simple test to check the polarity of the transformer windings. Connect a centre zero moving coil meter to the secondary winding, positive terminal to the dot marked transformer terminal. Take a battery of 3-6 Volt and connect it to the primary winding, positive terminal to the dot marked terminal. Watch which way the arrow deflects, it should deflect to the right. If it not, the winding marking is wrong

) Do I mark the red dots correctly in this problem, just suppose that current enters all 1st terminal?

 

You are wrong on all three cases.
At a guess, from the fact you have drawn arrows, you are still thinking of it in terms of current flow.

 

You are wrong on all three cases.
At a guess, from the fact you have drawn arrows, you are still thinking of it in terms of current flow.

oh, how to get the true understanding of these case?