In a properly biased transistor-

Options

A. both depletion layers are equially large.
B. both depletion layers are equally small.
C. Emitter-base depletion layer is large but base collector depletion layer is small.
D. Emitter-base depletion layer is small but base-collector depletion layer is large.

Answer

To solve the question regarding the depletion layer widths in a properly biased transistor, we can follow these steps:

### Step 1: Understand the Transistor Configuration
A transistor consists of three regions: the emitter, the base, and the collector. In a properly biased transistor, the base-emitter junction is forward-biased, while the base-collector junction is reverse-biased.

### Step 2: Analyze the Biasing Conditions
- **Forward Bias (Base-Emitter Junction)**: When the base-emitter junction is forward-biased, it allows current to flow easily. This results in a smaller depletion region because the majority carriers (holes in the p-type base and electrons in the n-type emitter) are pushed towards the junction, reducing the width of the depletion layer.

- **Reverse Bias (Base-Collector Junction)**: In contrast, when the base-collector junction is reverse-biased, it prevents current flow. This leads to a larger depletion region as the majority carriers are pulled away from the junction, widening the depletion layer.

### Step 3: Compare the Depletion Layer Widths
- The depletion layer width at the base-emitter junction is small due to forward bias.
- The depletion layer width at the base-collector junction is large due to reverse bias.

### Step 4: Conclusion
In a properly biased transistor:
- The depletion layer width at the base-emitter junction is small.
- The depletion layer width at the base-collector junction is large.

Thus, the correct answer is that the emitter-base depletion layer is small, while the base-collector depletion layer is large.

### Final Answer
The depletion layer width in a properly biased transistor is small at the base-emitter junction and large at the base-collector junction.

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