*Question T6B10:
Which of the following can provide power gain?*  

*Correct Answer is  B: Transistor*  

### AI Response: (may contain errors)  

To understand which component can provide power gain, let's analyze each option:

### Correct Answer: Transistor
- **Why it's correct**: A transistor is an active device that can amplify power. It takes a small input signal and produces a larger output signal, effectively increasing the power. The power gain of a transistor can be expressed as:

$$
P_{out} = P_{in} \times G
$$

where:
- $P_{out}$ = output power
- $P_{in}$ = input power
- $G$ = gain of the transistor (greater than 1)

### Incorrect Choices:
1. **Transformer**
   - **Why it's incorrect**: A transformer can change voltage levels and provide impedance matching, but it does not provide power gain. It operates on the principle of conservation of energy, meaning the output power cannot exceed the input power. The relationship can be expressed as:

   $$
   P_{in} = P_{out}
   $$

2. **Reactor**
   - **Why it's incorrect**: A reactor (inductor) stores energy in a magnetic field and does not amplify power. It can affect the phase and reactance in a circuit but does not provide gain. The power remains the same, and it primarily serves to store energy temporarily.

3. **Resistor**
   - **Why it's incorrect**: A resistor dissipates power as heat and does not provide any gain. The power across a resistor can be calculated using:

   $$
   P = I^2 R
   $$

   where:
   - $P$ = power in watts
   - $I$ = current in amperes
   - $R$ = resistance in ohms

   Resistors always reduce the power available to the rest of the circuit.

### Summary
- **Transistor**: Provides power gain by amplifying input signals.
- **Transformer**: Changes voltage but does not provide gain.
- **Reactor**: Stores energy without amplifying power.
- **Resistor**: Dissipates power and does not amplify.

Understanding these differences is crucial for the Extra Class exam and practical applications in amateur radio.