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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Physics => Topic started by: naved_s9994 on July 29, 2009, 04:33:02 pm

Title: Transformers
Post by: naved_s9994 on July 29, 2009, 04:33:02 pm: Can anyone please explain Transformers in General :

Also What happens when there are more turns at primary than secondary (vice-versa)
and general facts of transformers

Also whats the difference when in Q's theres some 'x amount RMS', and in the same question theres some 'x amount V' - like what do you do? what do they mean?

Thanks heaps !
Title: Re: Transformers
Post by: Flaming_Arrow on July 29, 2009, 04:49:04 pm: if there's more turns on the primary than seconday it means its a step down transformer(steps down voltage, steps up current)
Title: Re: Transformers
Post by: kurrymuncher on July 29, 2009, 04:51:38 pm: When there are more primary turns than secondary, the voltage will be stepped down. If there are more secondary turns than primary, then the voltage will be stepped up.

Transformers are used to reduce the power lost over transmission lines, eg between a generator and a city. Once the electricity is generated, it will travel through a step up transformer, which will increase its voltage to a much larger voltage. This massive increase in voltage will reduce the current in the wire. As the current is lowered, the power loss is minimised, as Ploss=I^2R. This voltage can then be stepped down to 240 volts, so it can be used in homes (lighting etc). Basically, transformers are used, as they are cost efficient. The only other ways to reduce power loss, would be to increase the resistance of the cables, but this would be nearly impossible, as it would cost ZILLIONS of dollars. Or the length of the transmission lines could be decreased but then again, this is not practical. Thats why transformers are efficient, they do not cost as much, and effectively reduce power loss.
Title: Re: Transformers
Post by: naved_s9994 on July 29, 2009, 05:38:38 pm: Ahh thanks KM and F_A !!

Also, Ideal transformer Non Ideal Transformer?
Title: Re: Transformers
Post by: kurrymuncher on July 29, 2009, 05:40:29 pm: Ideal transformers are 100 % efficient, meaning that no power is lost. If you want to check if a transformer is ideal, just touch it. If it is hot, that means power has been lost( electrical energy has been converted to heat energy). If it isn't hot, then it is ideal.
Title: Re: Transformers
Post by: TrueTears on July 29, 2009, 05:54:01 pm: Non ideal transformers tend to use power due to eddy currents in the iron core.
Title: Re: Transformers
Post by: naved_s9994 on July 29, 2009, 05:58:53 pm: I.E TT, you mean ideal transformers, do NOT use power?
Title: Re: Transformers
Post by: kaanonball on July 29, 2009, 07:00:23 pm: Quote from: naved_s9994 on July 29, 2009, 05:58:53 pm
I.E TT, you mean ideal transformers, do NOT use power?

They mean that, and ideal transformer does not lose any power as a result of excess heat generated by the coils or as TT was saying due to eddy currents.

So the power generated in the primary coil = power generated in the secondary coil
Title: Re: Transformers
Post by: naved_s9994 on July 29, 2009, 07:47:55 pm: I.e does this also mean that in an ideal transformer

V1 = V2
I1 = I2
N1 = N2

?
Title: Re: Transformers
Post by: Flaming_Arrow on July 29, 2009, 07:50:43 pm: $\frac{v_2}{v_1}= \frac{n_2}{n_1} = \frac{I_1}{I_2}$
Title: Re: Transformers
Post by: TrueTears on July 29, 2009, 08:31:27 pm: Quote from: naved_s9994 on July 29, 2009, 05:58:53 pm
I.E TT, you mean ideal transformers, do NOT use power?
...
...
If there is a current and voltage... how can there be no power?
Title: Re: Transformers
Post by: appianway on July 29, 2009, 08:45:47 pm: I think he means no power is dissipated. After all, the formula P = VI refers to the voltage drop across two points and the current flowing.
Title: Re: Transformers
Post by: kaanonball on July 29, 2009, 09:45:46 pm: Quote from: naved_s9994 on July 29, 2009, 07:47:55 pm
I.e does this also mean that in an ideal transformer

V1 = V2
I1 = I2
N1 = N2

?

In response to your question, $V_1$ and $V_2$ are different, as the transformers purpose is to change the value of $V_1$ , either stepping it up(increasing its value) or down(decreasing its value). otherwise there would be no point using a transformer.

$I_1$ and $I_2$ are also different, as a consequence of changing the value of voltage in an ideal transformer the values of current will be altered so that $P_1=P_2$ keeps true

$N_1$ and $N_2$ must be different in order to step up/down voltage/current, otherwise the induced current/emf in the secondary coil would be the same as the supplied emf/current in the primary coil

for further clarification

the term 'ideal' only refers to power, so an 'ideal' transformer is 100% efficient, hence no loss of energy.

this means $P_{primary} = P_{secondary} <br /> i.e. V_{primary}*I_{primary} = V_{secondary}*I_{secondary}$
Title: Re: Transformers
Post by: /0 on July 29, 2009, 09:56:33 pm: Yes, do not use $I_1V_1=I_2V_2$ unless the question states the transformer is ideal.