JFET terminals – basic identification: The three external connections (“legs”) of a JFET are the drain, the gate, and the ______.

Introduction / Context:
Correct terminal identification is essential when biasing and measuring field-effect transistors. A JFET has three functional terminals that define how the channel is controlled and how current flows.

Given Data / Assumptions:

• Discrete JFET device (n- or p-channel).
• Standard three-terminal configuration.
• Common symbols and pinouts used.

Concept / Approach:
The JFET channel is the conduction path between the drain and source. The reverse-biased gate–channel junction modulates the channel width. The three terminals are named drain (D), source (S), and gate (G); “channel” is not a terminal.

Step-by-Step Solution:
Identify current path: drain ↔ source.Identify control: gate reverse-bias alters depletion region and channel width.Therefore, the third terminal besides drain and gate is the source.

Verification / Alternative check:
Schematic symbols label D, S, and G; datasheets provide pin numbering for specific packages.

Why Other Options Are Wrong:
“Channel” describes the region, not a terminal.

“Substrate” is relevant in MOS technology; a discrete JFET presents three leads only.

“Cathode” and “emitter” are diode/BJT terms, not JFET terminals.

Common Pitfalls:
Misidentifying source and drain can matter in devices with asymmetric pinch-off behavior; always consult the datasheet pinout.

Final Answer:
source