Question

For what value of Vgs, the drain current will be 1/4th of its maximum current?

(a) 0

(b) 1

(c) Vp

(d) Vp/2

I got this question in examination.

I'd like to ask this question from The Pinch off Voltage Vp in section Field-Effect Transistors of Electronic Devices & Circuits

Answer 1

Right choice is (d) Vp/2

The best I can explain: ID=IDSS (1-Vgs/Vp)^2

When  ID=IDSS/4 => (1-Vgs/Vp)^2 = 1/4

=>(1-Vgs/Vp)^2=1/2

=>Vgs=Vp/2.