I need a transformer calculation refresher! (Basic maths refresh)

[WyverntekGameRepairs]

Hi, I need a refresher on this subject because it has been a long while since I calculated transformer windings' specs.
I thought it would be best to put it here so others can learn from it too.
I need to relearn three different basic things:
1) How to calculate the Primary:Secondary number-of-turns ratio
2) How to calculate voltage change in respect to the P:S ratio
3) How to calculate current change in respect to the P:S ratio

These three things are the basic fundamentals for transformer design, and are important to any hobbyist or person who wants to learn how to build or implement a proper transformer into their projects or designs. (Or if you are like me and need a refresher course to get rusty gears turning again ). There are tutorials online, but I think that it is better that anyone can come here and get an answer too.

[Jwillis]

Google's awesome.  http://www.learnabout-electronics.org/ac_theory/transformers01.php

[vu2nan]

The relationship is quite simple.

Np / Ns = Vp / Vs = Is/Ip

Where Np = primary turns, Ns = secondary turns, Vp = primary voltage, Vs = secondary voltage, Ip = primary current and Is = secondary current.

Regards,

Nandu.