Step up, step down (1 Viewer)

[The Bograt]

What is the differences between step up and step down transformers and what do they do?
Thanks

 

[smegthehead]

step up transformers- step up the voltage by using a primary coil of wire to induce a change of flux in a secondary coil which has more turns in it, which means there is a greater change of flux, and by faradays law a bigger voltage is induced.

step down transformers- basically the same principle except that the magnetic field is initially created in the bigger coil and causes a change in flux in the smaller coil.

what they do- when energy companies transmit power over large distances, they want to save as much money as possible by reducing the amount of power lost through heating. this is done by stepping up the voltage. Because power=volts x current, as the voltage goes up, the current goes down. However when the lines are closer to homes, the voltage is stepped down so that it is safe enough for houshold use

 

[The Bograt]

Hmmm wouldn't it be the other way round?

In a step up shouldn't there be less coils in the secondary, therefore inducing a smaller current hence a larger voltage

And in a step down more coils in the secondary to induce a greater current and therfore lower the voltage?

 

[smegthehead]

you would think that, however faradays law can be adapted to look like:

emf= (number of turns) x [(change in flux)/(change in time)]

in other words, the emf generated is in proportion to the number of coil turns that experience a flux change (due to the alternating current that is being fed into the primary coil). this means in a bigger coil, there is a bigger emf, and hence a smaller current

 

[The Bograt]

there is a bigger emf, and hence a smaller current

I'm sorry but I don't understand that.

Thanks for all the help by the way

 

[smegthehead]

an emf is the same thing as a potential difference, or a voltage. What we have to think about now is conservation of energy. Even though the voltages and currents on either side of the transformer are different, the power in the entire system has to remain as a constant, or else we'd be pulling energy out of nowhere (which can't happen). Therefore:

Power going in = power going out

Power can be described by the equation P=VI, where power is in watts, voltage(or emf) is in volts, and current is in amps. Seeing as the power has to stay the same, the only variables in this instance are the voltage (emf), and current. Therefore to maintain a constant value for P, if the voltage goes up, the current must go down, and vice versa.

hope that helps matey

 

[The Bograt]

*click*
Thanks mate I get it now
Just got confused that a greater change of flux is produced in step up, which means greater emf, and therefore less current.

 

[smegthehead]

glad i could help matey