For the n-channel enhancement MOSFET shown in the given

For the n-channel enhancement MOSFET shown in the given figure, threshold voltage V_tn = 2V. The drain current I_D of the MOSFET is 4 mA when drain resistance R_D is 1 kΩ. If value of R_D is increased to 4 kΩ, then drain current I_D will become _______ mA .

I_D = K(V_GS – [V_E(TH)]²
⇒ 4mA = K (V_GS – 2)²
Here, V_GS = 10 – 4 × 1 = 6
∴ 4 = K(6 – 2)²

⇒ K =	4	=	1
	16		4

When R_D is increased to 4 kΩ,
V_GS = 10 – 4I_D

Now , I_D =	4	(10 – 4I_D - 2)²
	16

⇒ 4I_D = (8 – 4I_D)² = 64 + 16 I_D² – 64 I_D
⇒ 16I_D² – 68 I_D + 64 = 0
⇒ 4I_D² – 17 I_D + 16 = 0
⇒ I_D = 2.8 mA