# Transformers - Find n1 and n2

## Homework Statement

[PLAIN]http://img192.imageshack.us/img192/8428/circuits.png [Broken]

## Homework Equations

$\frac{V_L}{V_s} = \frac{nR_L}{n^2 R_s + R_L}$

$R_s = \frac{R_L}{n^2}$

$P = \frac{V_L^2}{R_L}$

## The Attempt at a Solution

How should I go about solving this problem? Do I have to convert it to an equivalent circuit? If so how would the end result look exactly? I haven't seen any good examples in the book of creating equivalent circuits of transformers so I'm a little unsure of what to do.

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NascentOxygen
Staff Emeritus
It looks like n2 is their way of expressing the turns ration of that transformer, 1:n2. So in place of the transformer with 8k in its secondary, you can show a new resistor RS in series with your resistor R, that new resistor bring RL transformed by the square of the turns ratio, as they indicate.

It looks like n2 is their way of expressing the turns ration of that transformer, 1:n2. So in place of the transformer with 8k in its secondary, you can show a new resistor RS in series with your resistor R, that new resistor bring RL transformed by the square of the turns ratio, as they indicate.

In part a) I found n2 to be 10, but how do I find the max power now? I used the equation I posted in the OP to find the load voltage then used $P=\frac{V_L^2}{R_L}$ but I get 115.2 W as power when the book has 10,000 W roughly. Perhaps it's because I use the wrong value for $R_s$. I used 20 Ohms. Should it be different? Or it could be because of the n value I use. I put in 10.

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NascentOxygen
Staff Emeritus
In part a) I found n2 to be 10
as do I
but how do I find the max power now?
Are you talking about part (a) or part (b)?
I used the equation I posted in the OP to find the load voltage then used $P=\frac{V_L^2}{R_L}$ but I get 115.2 W as power when the book has 10,000 W roughly.
It can't be thousands of watts. Isn't that a 20 ohm source resistance? So you want the transformed impedances to be of that order, too, so the current from the 120v source is going to be less than 3 amps. (Even were you to short circuit the transformer windings, that 20 ohm will limit the current to 6 amps.)
Perhaps it's because I use the wrong value for $R_s$. I used 20 Ohms. Should it be different?
I see nothing to indicate a different Rs.
Or it could be because of the n value I use. I put in 10.
In part (b) you are told n1 is 5, and required to find the new n2. So there is no place for using an n of 10.

FWIW, I calculate 1.3125 A is drawn from the 120v supply, in part (b).

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as do I

Are you talking about part (a) or part (b)?

It can't be thousands of watts. Isn't that a 20 ohm source resistance? So you want the transformed impedances to be of that order, too, so the current from the 120v source is going to be less than 3 amps. (Even were you to short circuit the transformer windings, that 20 ohm will limit the current to 6 amps.)

I see nothing to indicate a different Rs.

In part (b) you are told n1 is 5, and required to find the new n2. So there is no place for using an n of 10.

FWIW, I calculate 1.3125 A is drawn from the 120v supply, in part (b).

Yeah I was talking about part a) Apparently some others were able to get the 10,000 W power for part a that was int he back of the book though I couldn't really follow what they did.