*Question T6D06:
What component changes 120 V AC power to a lower AC voltage for other uses?*  

*Correct Answer is  B: Transformer*  

### AI Response: (may contain errors)  

The correct answer to the question is **B: Transformer**. 

### Explanation of the Correct Answer:
- A **transformer** is an electrical device that changes the voltage of alternating current (AC) power. It operates on the principle of electromagnetic induction and can step down (reduce) or step up (increase) the voltage level. 
- The relationship between the primary and secondary voltages and the number of turns in the coils is given by the formula:
  
  $$ 
  \frac{V_p}{V_s} = \frac{N_p}{N_s} 
  $$

  where:
  - $V_p$ = primary voltage
  - $V_s$ = secondary voltage
  - $N_p$ = number of turns in the primary coil
  - $N_s$ = number of turns in the secondary coil

### Why the Other Choices are Incorrect:
- **A: Variable capacitor**  
  - A variable capacitor is used to change capacitance in a circuit, not to change voltage levels. It is typically used in tuning circuits, such as in radios.

- **C: Transistor**  
  - A transistor is a semiconductor device used for amplification or switching. It does not change AC voltage levels; instead, it can control current flow in a circuit.

- **D: Diode**  
  - A diode is a semiconductor device that allows current to flow in one direction only. It is used for rectification (converting AC to DC) but does not change the voltage level of AC power.

### Summary:
- The transformer is the only component listed that specifically changes AC voltage levels, making it the correct answer. Understanding the function of each component is crucial for the Extra Class exam.