when i connected a digital voltmeter to a piezo crystal and applied force on crystal, multimeter shows 12 volt. But when same crystal is connected to analoge voltmeter and same force is applied it shows only 0.12 volt. Why is this difference?
It is a power consumption thing. To make a digital display change form 0.01 to 1.00 is no different in terms of the power requirement. To move a needle against a spring takes more power to go from 0.01 to 1.00. A piezo crystal does not have much power, but can generate huge voltages (enough to cause a spark for a candle lighter) which are thousands of Volts. So basically the internal resistance of the analog voltmeter is higher than that for a digital voltmeter. The law that acts here is Ohm's law, Voltage (V) = Current (I) X Resistance (R). That's my stab at answering your question, however it really doesn't have much to do with nanotechnology !!
Good luck, Jan