Question

What is the principle of transistor?

Answer 1

The principle of a **transistor** is based on **controlling the flow of current** using a small input signal.

In simple words:

A **transistor** acts like a **switch** or an **amplifier**. It uses a **small current or voltage at its input** (called the **base** in a BJT or **gate** in a FET) to **control a larger current** flowing between two other terminals (called **collector-emitter** in BJT or **drain-source** in FET).

---

### For BJT (Bipolar Junction Transistor):
- It has **three terminals**: **Base (B), Collector (C), and Emitter (E)**.
- A **small current** at the **base** controls a **large current** from **collector to emitter**.
- Principle: **Current control device**

### For FET (Field Effect Transistor):
- It has **three terminals**: **Gate (G), Drain (D), and Source (S)**.
- A **small voltage** at the **gate** controls a **large current** from **drain to source**.
- Principle: **Voltage control device**

---

### Summary:
- **Small input → Controls → Large output**
- Works like a **valve for current**.
- Can **amplify signals** or act as an **electronic switch**.

Would you like a simple diagram to visualize this?