Voltage v_{gs} will swing along the dc load line of Fig 4-6(b) (which is now identical to the ac load line) from point a to point b, giving, as extremes of i_D, 3.1 \text{mA} and 0.4 \text{mA}. The corresponding extremes of v_S = i_DR_S are 6.2 \text{V} and 0.8 \text{V}.