In an n-p-n transistor connected in common emitter configuration, I have drawn a graph of the input and output characteristics. Using these two graphs, it is easy to find the input and output impedance - using the slope. However, I do not know how to relate this to the voltage and current gain. Is there a formula to do so?
In most cases, the ouput resistance of the BJT (rather large) is neglected in parallel to the external collector resistor, which mainly determines the voltage gain. More than that, this gain is also determined by the transconductance gm, which is the slope of the transfer characteristic Ic=f(Vbe). Hence, the characteristics mentioned by you do not help finding the voltage gain of the stage.