*Question E6A08:
What is the term for the frequency at which the grounded-base current gain of a bipolar junction transistor has decreased to 0.7 of the gain obtainable at 1 kHz?*  

*Correct Answer is  D: Alpha cutoff frequency*  

### AI Response: (may contain errors)  

The correct answer to the question is **D: Alpha cutoff frequency**. Here's a breakdown of why this is the case, along with explanations for the other choices.

### Explanation of the Correct Answer:
- **Alpha cutoff frequency** refers to the frequency at which the current gain (alpha, $\alpha$) of a bipolar junction transistor (BJT) drops to 0.7 of its value at a reference frequency, typically 1 kHz. This is an important parameter in understanding the frequency response of BJTs.

### Why the Other Choices are Incorrect:
- **A: Corner frequency**  
  - This term generally refers to the frequency at which the output power of a system is reduced to half its maximum value (or -3 dB point). It is not specific to BJTs and does not relate to the gain dropping to 0.7.

- **B: Alpha rejection frequency**  
  - This term is not commonly used in the context of BJTs. It may imply a frequency where alpha is rejected or minimized, but it does not specifically describe the gain behavior of a BJT.

- **C: Beta cutoff frequency**  
  - Beta ($\beta$) is the current gain of a BJT in common-emitter configuration. The beta cutoff frequency would refer to the frequency at which beta drops to a certain level, but the question specifically asks about alpha, not beta.

### Useful Formulas and Rules of Thumb:
- The relationship between alpha ($\alpha$) and beta ($\beta$) for a BJT is given by:
  
  $$\beta = \frac{\alpha}{1 - \alpha}$$

- The cutoff frequencies for BJTs are important for designing amplifiers and understanding their frequency response. The alpha cutoff frequency is particularly relevant for applications where low-frequency performance is critical.

In summary, the alpha cutoff frequency is a key parameter in the performance of BJTs, and understanding it helps in designing circuits that utilize these transistors effectively.