How do transformers work, and how to read dot notation

[eft]

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Hi all, I have attempted this question but have a few queries on how transformers work, and what the dot notation represents.

(a) The flux would be clockwise around the iron core.

(b) This is the question where it gets a bit iffy. So from my understanding, the dot notation would indicate that terminal 4 is positive. Is this because of the clockwise magnetic flux flowing through the iron core, and due to lenz law the coil will have a voltage induced in such a way to oppose the change. That is, the voltage induced in the secondary coil will produce an anticlockwise flux that opposes the initial flux producing it? That will mean that the positive charges will flow towards terminal 4 and hence make it positive.

(c) If we were to connect terminal 3 and 4 by a wire, then current would flow from 4-->3 (using the right-hand grip rule I deduced that current would flow to the right as indicated on the diagram).

In my head, the secondary coil somewhat acts like a battery since current flows the same direction as the voltage difference between terminal 3 and 4.

I don't really feel confident for all of these answers, so please explain what I am missing if I am wrong! Thanks!

 

[gneill]

Hi eft,

Welcome to Physics Forums!

It looks like you've got a handle on transformers. Your thoughts and analyses look fine.

To answer your question in the thread title, dot notation on schematic diagrams allows the designer to convey to anyone who needs to "read" the diagram how two (or more) inductively coupled coils relate to each other in terms of their winding directions. The basic rule is, a current flowing into the dot on one coil will produce a current out of the dot on the coupled coil.

When doing circuit analysis on a circuit with coupled inductors, one has to be careful to make sure that one makes the induced currents flow in the right direction, which depends on ones assumed loop or branch current directions and whether they flow into or out of the dots in their circuit.