Q.What is the function of drain?

Every JFET has three terminals, each with a clear job. Learning their functions is a standard one- and two-mark exam expectation.

• Source (S) — the terminal through which the majority charge carriers enter the channel. It supplies the carriers that take part in conduction.
• Drain (D) — the terminal through which the carriers leave the channel. It collects the carriers delivered by the source; the current entering here is the drain current $I_D$.
• Gate (G) — the controlling terminal. When a suitable (reverse-bias) potential is applied to the gate, the electric field it produces widens or narrows the channel and so controls the flow of carriers through it. Because the gate junction is reverse biased, the gate itself draws almost no current. …