#1
In the genre of rock and pop music what generally determines the change from the Major Key to the relative Minor Key? Like if the song in the beginning was in C major and then the chorus went to A minor.

In order for the key change to take effect does it need to follow the same rules like where that particular section of the song resolves on A minor or A chord often enough to establish the A minor Key?

I just wanted to see if I am correct and am looking for some clarification on this subject. thank you whoever can help.

And can anyone maybe give me simple popular songs that have these concepts? Thanks
#2
I don't really think it needs to, if anything it's probably better to have a different chord (F major, G major, in your case of C. It can be any chord really). Essentially you're still in the same key, because it's all the same notes, it's just a different feel being based on a certain chord.

For example with this song: http://www.youtube.com/watch?v=mJXT26X4Yls
It stays mostly in A minor, but the Chorus is in C Major (Starting on the C Chord)
The way it resolves from the pre-chorus is going E and D notes in octave shapes.

You don't have to leave it as relative keys, you can go to other keys in a song (Last chorus of Livin' on a Prayer by Bon Jovi, is in G minor (a minor 3rd up from the rest of the song) it's just a case of experimenting sometimes with key changes, I guess
#3
Basically for a key to change it needs to resolve to a new tonal center. You're correct in thinking that some songs resolve to the relative major/minor with a key change but arguably more popular is shifting up the whole progression/tonal center by a tone or more.

Popular examples (from memory):

To the relative major/minor;
Little Wing - Hendrix
Comfortably Numb - Pink Floyd

Shifting up:
My Heart Will Go On - Celine Dion
Son Of A Preacher Man - Dusty Springfield
Think - Aretha Franklin
And no, Guitar Hero will not help. Even on expert. Really.
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#4
Be careful with the A minor assumption. If you know your theory, you'll realize that Am is the vi scale degree of C major, or the relative minor. You need to analyze the chords around it to see what's going on. Most of the time, in Rock and Pop, we'll have a key change part way through the song that takes us up a half or whole step. It's usually pretty obvious and sticks out like a sore thumb when it happens. That's not to say we couldn't change keys during the chorus. Also don't discount the idea that an accidental is being used and that a key change really hasn't occured.