State briefly the underlying principle of a transistor oscillator. Draw a circuit diagram showing how the feedback is accomplished by inductive coupling. Explain the oscillator action.

Explanation

### Step-by-Step Solution

**Step 1: State the Underlying Principle of a Transistor Oscillator**
The underlying principle of a transistor oscillator is **mutual induction**. This principle states that a changing current in one coil induces an electromotive force (EMF) in another nearby coil.

**Step 2: Draw the Circuit Diagram**
A basic circuit diagram of a transistor oscillator using inductive coupling includes:
- An NPN transistor
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