Transistors can work as a switch in

Options

A. Saturation region
B. Active region
C. Cut off region
D. Both (1) and (3)

Answer

To determine how transistors can work as a switch, we need to understand the different operating regions of a transistor and how they relate to switching applications.

### Step-by-Step Solution:

1. **Understanding Transistor Operation**:
- A transistor can operate in three main regions: cut-off, active, and saturation.
- In the cut-off region, the transistor is OFF, meaning no current flows through it.
- In the saturation region, the transistor is ON, allowing maximum current to flow.

2. **Identifying Switching States**:
- For a transistor to function as a switch, it needs to be able to switch between the ON and OFF states.
- The ON state corresponds to the saturation region, while the OFF state corresponds to the cut-off region.

3. **Evaluating the Options**:
- **Option A**: This option states that transistors can work as a switch in the saturation region (ON) and cut-off region (OFF). This is correct.
- **Option B**: This option suggests that transistors can work as a switch in the active region. However, in the active region, the transistor does not fully turn ON or OFF, which makes it unsuitable for switching applications. This option is incorrect.
- **Option C**: This option also states that transistors can work as a switch in the saturation and cut-off regions, which is correct.
- **Option D**: This option claims that both options 1 (A) and 3 (C) are correct. Since both A and C are indeed correct, this option is also correct.

4. **Conclusion**:
- The correct options for how transistors can work as a switch are options 1 (A) and 3 (C), which are both valid. Therefore, option D, which states that both 1 and 3 are correct, is the right choice.

### Final Answer:
The correct option is D: Both 1 and 3.