help me...

i wana experiment on blood, effect of alternating current on human blood, but problem z i dnt know how i can reduce voltage to minimal level, plz guide me about it.

thanks..

When you say minimal, are you talking milivolts, microvolts or something even lower? Depending on the total drop in voltage from whatever source you intend to use, a simple voltage divider would be the first choice. How much current do you want to deal with? How steady does the voltage have to be held? Does it have to be adjustable? I assume that you don’t want to put enough power into your sample to cause it to boil but, it is possible since you have not specified any parameters.

in millivolts..and it sholud b adjustable and steady

Come on friend, provide the details. What are you using for the voltage source and at what value? How adjustable, over what range and to what accuracy? How stable in either % or an absolute value over what time frame and what range of current? In other words, what is the resistance range of the samples you intend to work with?

If you want a real answer, you have to provide a real question.
At a guess, I would say use step down transformer to get to the 2 to 12 volt range. Then a resistive voltage divider made of a resister and a potentiometer. The details control the values of the components.