View attachment 96302
current follows the lowest resistance path ..that is why for a current amplifier, signal (current) to pass the input impedance must be as low as possible (ideally zero)..in the above figure as the value of Zin is decreased the current flowing through increases and the current amplification which is "Ai*current in Zin" also increases.
View attachment 96303
similarly in the volatage amplifier if the input resistance is high the voltage drop across it will also be high.. in the above figure as the value of Rin (input resistance ) increases the voltage across also increases and hence the voltage amplification.