Q. Draw the common source drain and transfer characteristics of a JFET. How are they useful?

The graph below shows  variation of the drain current Id as a function of the drain voltage (Vds) for various values of the gate voltage (Vgs) in an n-channel JFET. The current decreases and the pinch-off occurs at lower drain voltages as the gate is made more negative. At any drain voltage, The drain current reduces to zero  if the magnitude of gate voltage becomes equal to the magnitude of pinch-off voltage (Vp) . We have a general relation:

V_ds = V_gs + V_p

The sharp increase in the drain current at higher drain voltages is due to the breakdown.