Consider the JFET circuit given below

Consider the JFET circuit given below—
Current I_D is given by
Assume I_D = 12 1 + V_GS ² mA—
4

The given circuit

From given circuit V_GS = V_G – V_S = 0 – V_S
(Since V_G = 0V and V_S = I_DR_S)
or V_GS = – I_DR_S = – I_D.1 kΩ

Now, I_D = 12		1 +	V_GS		²	mA
			4

Now, I_D = 12		1 -	I_D		²
			4

or I_D = 12		1 +	I_D²	– 2.1.	I_D
			16		4

or I_D = 12		16 + I_D² – 8I_D
		16

or 4 I_D = 48 + 3 I_D²– 24 I_D
or 3 I_D² – 28 I_D + 48 = 0

or I_D =	28 ± √28₂ – 4 × 3 × 48
	2 x 3

I_D = 2·26 mA
Hence alternative (A) is the correct choice.

Assume I_D = 12 1 +	V_GS	²	mA—
	4