*Question E6F08:
Why are optoisolators often used in conjunction with solid-state circuits that control 120 VAC circuits?*  

*Correct Answer is  C: Optoisolators provide an electrical isolation between a control circuit and the circuit being switched*  

### AI Response: (may contain errors)  

Optoisolators are crucial components in circuits that control high-voltage systems, such as 120 VAC circuits, due to their ability to provide electrical isolation. Let's break down the correct answer and the other choices.

### Correct Answer: 
**C: Optoisolators provide an electrical isolation between a control circuit and the circuit being switched.**

- **Explanation**: 
  - Optoisolators consist of a light-emitting diode (LED) and a photodetector (like a phototransistor) housed together. When the LED is activated by the control circuit, it emits light that the photodetector senses, allowing the control circuit to influence the power circuit without any direct electrical connection.
  - This isolation is critical for safety, as it protects the low-voltage control circuit from high voltages present in the power circuit, preventing damage and reducing the risk of electric shock.

### Why the Other Choices are Incorrect:

- **A: Optoisolators provide a low-impedance link between a control circuit and a power circuit.**
  - **Incorrect**: Optoisolators do not provide a low-impedance link; rather, they create a high-impedance barrier. This is essential for isolation, as it prevents direct electrical contact between the two circuits.

- **B: Optoisolators provide impedance matching between the control circuit and power circuit.**
  - **Incorrect**: Impedance matching is not the primary function of optoisolators. Their main role is to isolate circuits, not to match their impedances. Impedance matching is more relevant in RF applications to maximize power transfer.

- **D: Optoisolators eliminate the effects of reflected light in the control circuit.**
  - **Incorrect**: While optoisolators use light for signal transfer, they do not specifically address reflected light issues. Their function is based on the transmission of light from the LED to the photodetector, and they are designed to operate effectively regardless of reflected light.

### Summary:
Optoisolators are essential for safely interfacing low-voltage control circuits with high-voltage power circuits by providing electrical isolation. This prevents potential hazards and protects sensitive components. Understanding their function and the reasons why other options are incorrect is key for the Extra Class exam.