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cant understand this circuit

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nabliat6

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**broken link removed**
the dot above the coil says that the voltage goes from top to buttom
i cant see how v3 needs to show is the sum or subraction of them both.

i can recognize the sum of two potentials when we connect the high potential of the first with the low potential of the second
and measure the other two ends with the volmeter
but he i cant see where they "connect the high potential of the first with the low potential of the second"
?
and where is the other ends?
 
V3 could show just about anything.

V1 shows the input voltage, which is what comes from the AC supply.
V2 shows the output voltage, which is approximately the transformer ratio times the AC supply.

However, there is no return path for V3, because the transformer isolates. In practice, stray capacitance, details of transformer construction and impedance of the voltmeter would all affect the reading of V3. There would be next to no current flow if V3 were replaced with an ammeter. That would not be the case with V1 or V2.

If one of the connections on the secondary of the transformer were connected to one side of the primary, then the voltage on V3 would be defined. For instance, if the two connections on the transformer with dots were connected, you would get V3 = V1-V2.
 
return path mean a way through which electrons can go home. just like when we connect a battery to any circuit, electrons emit from -ve terminal and running through the circuit it return to the Battery through +ve terminal.
 
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This is AC so + and - are not relevant.

The dot indicates the phase.

In this case, V3 makes no sense as the primary is isolated from the secondary there is no return path, so V3 is effectively zero.
 
OK, to start understanding have a look at the attachment.

JimB
 

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  • Transformer Phas&#105.JPG
    Transformer Phas&#105.JPG
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This is why JPEGs are so bad, evey time they're edited, they get more fuzzy.

I've done my best to defuzz it.
 

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  • transformer V3..PNG
    transformer V3..PNG
    6.6 KB · Views: 297
Just to clarify on Hero and JimB's comments, the dot notation indicates the following: when the dot end of the primary goes positive, the dot end of the secondary goes positive too. Likewise in the negative direction.

So to quote you:

the dot above the coil says that the voltage goes from top to buttom

is not strictly true, as the voltage could be going in either direction. The 2 dotted ends go up and down together, regardless of what their instantaneous voltage is (which is what your point was implying)

JimB's answers are correct if the turns ratio is 1:1 - ie there are the same amount of turns on the primary as secondary
 
JimB's answers are correct if the turns ratio is 1:1 - ie there are the same amount of turns on the primary as secondary

JimBs answers are also correct if the ratio in not 1:1.

However, to overcome the awkwardness of a minus sign, I will rewrite one of the expressions as:

V3 = |V1 - V2|

JimB
 
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