Question

why we are using four probe method instead of two probe method in physics practical

Answer 1

Four point probe method is used simply for resistivity measurement. The reason using four probes instead of two by having force and sense probes is to eliminate contact resistance and increase accuracy. If the current used is not constant and has a time varying components, the parasitic probe capacitance and inductance would affect the measurement hence reduce the accuracy of the measurement. Also since pure resistance is a DC measurement, there is really no reason for not using a constant current.