Thanks for the clear answer i still have some questions to ask.
How do i calculate the RB, RC, RE ?
Is the max safe BJT base current 1/10 of the max safe collector current usually?
Does the transistor cause a 0.7 voltage drop between c and e or is it just the base emitter junction ?
For a transistor with 100hfe to switch a load of 50ma @9v on its collector on what should the base current and voltage be to do the following:
To fully saturate the base emitter junction ?
Put the transistor just enough in the active region to prevent overheating ?