*Question T6C09:
What is component 4 in figure T-2?*  

*Correct Answer is  D: Transformer*  

### AI Response: (may contain errors)  

To determine what component 4 is in figure T-2, we need to understand the characteristics of each option provided.

### Correct Answer: Transformer

- A transformer is an electrical device that transfers electrical energy between two or more circuits through electromagnetic induction. It typically has two or more windings (coils) and is used to step up or step down voltage levels in a circuit.

### Why the Other Choices are Incorrect:

- **A: Variable inductor**
  - A variable inductor is a component that allows for the adjustment of inductance. It usually consists of a coil with a movable core. It does not have the distinct winding structure of a transformer.

- **B: Double-pole switch**
  - A double-pole switch is a mechanical switch that controls two circuits simultaneously. It does not have any inductive or transformer-like properties and is used for switching rather than energy transfer.

- **C: Potentiometer**
  - A potentiometer is a variable resistor used to adjust voltage levels in a circuit. It typically has three terminals and does not function as a transformer, which involves magnetic coupling between coils.

### Summary

In summary, the correct answer is a transformer because it is characterized by its ability to transfer energy through inductive coupling, which is not the case for the other components listed. Understanding the function and structure of these components is crucial for identifying them in circuit diagrams.