Key Help!

i posted on another instructors thread looking for u and also nothing to do with the topic does that make me a bad person or too egar? lol im sry here is the question again

ok i have played tabs for 2 years and was starved for the theory you are dishing out i am enjoying it all and i thank you. but for the past 2 nights at work i have racked my brain on this.

does the key of a piece equal the root of the main scale used in the piece ?

i know this may not be the topic for this thread if so im sry but my brain now hurts i was ready to start my minor pentatonic scale practice when i noticed that if i use say a scale of B major (B,C#,D#,E,F#,G#,A#,
2212221 the root is B. the key would have 5 sharps in it using the circle of fifths i can see A# is 7th or the last sharp 1 dagree up is B. KEY OF B EQUALS the B scale meaning that the scale of B major is the heart of our piece
here is the confusion
say i now use the same B scale only in minor pentatonic. (B,D,E,F#,A, 32232
now this key according to what i have learned should only have 1 sharp F# 1 dagree up is G !!!!!
WHAT key of G? shouldn't in still be KEY OF B I used a B scale?
how do i know that im supposed to use a B minor pentatonic scale for the most part if the key is G?
back to my question shouldnt the key equal my root note B?
please put my mind at ease thanks
WING.